Master Diver Award

Lecture Notes July 2009

Cover picture: Diver and Deeplet Sea Anemone © Gordon MacSkimming, ( www.pixsub.com )

Scottish Sub-Aqua Club The Cockburn Centre, 40 Bogmoor Place, GLASGOW, G51 4TQ Tel +44 (0)141 425 1021 Fax +44 (0)141 425 1021 www.scotsac.com

ScotSAC has prepared this document in accordance with the best available information at the time of writing. Any other persons who use any information contained herein do so at their own risk.

© ScotSAC 2009

Acknowledgements With grateful thanks to all the Scottish Sub-Aqua Club members for all their help and time in preparing this lecture note booklet. Special thanks go to:

• Don Lees (Borders)

• Andy Murray (Strathclyde University)

• Iona Murray (Strathclyde University)

• Andy Parks (Grampian)

• Alex Gallego (Grampian)

• Adam Curtis (Clydebank)

• Gordon McSkimming (www.pixsub.com) (West Lothian)

• Gerry Doherty

• Nigel Spike (Glasgow Academy)

• Dr Wilmot (West Lakes)

• Authors of previous Scottish Sub-Aqua Club Dive Training Manuals

Some images within Lecture 6 are reproduced by permission of the Controller of Her Majesty’s Stationery Office and the UK Hydrographic Office (www.ukho.gov.uk). © British Crown Copyright. Not to be used for navigation.

Disclaimer Although the Scottish Sub-Aqua Club have made every effort to ensure that the information contained in training materials was correct at time of going to press, they accept no responsibility for any loss, injury or inconvenience sustained by any person using the knowledge gained from them. Diving products featured throughout these notes are for illustrative purposes only and are not an endorsement or recommendation by Scottish Sub-Aqua Club. Unless otherwise specified, all photographs throughout this lecture series are Copyright Don’s Dive Store 2008.

Reference to ‘He’, ‘Him’ or His’ throughout this document also refers equally to ‘She’, ‘Her’, ‘Hers’.

Master Diver Award Introduction The Scottish Sub-Aqua Club (ScotSAC) Sport Diver award provides a core level of knowledge and dive training which equips divers with knowledge and skills required for sport diving to 30m. The Master Diver award prepares the diver for a wider range of diving. Building on the skills gained during Sport Diver, the Master Diver award is designed to provide a greater understanding of the physics of diving, and brings more focus to safety and dive planning aspects. On completion of the award, the diver will have gained significant experience in diving at a range of depths and conditions, and be competent in dive leading and expedition organisation. The Master Diver Award consists of a number of elements:

• A series of 8 Lectures, covering advanced topics of scuba diving

• A written lecture assessment

• 10 open water assessments, building on experience as a Sport Diver

• A minimum number of dives to varying depths and conditions. Once completed, the diver will receive an internationally recognised award which allows them to dive to a maximum depth of 40m. This lecture series is designed to be used in conjunction with the Scottish Sub-Aqua Club ‘Sport Diving’ manual, and follows the format of the Scottish Sub-Aqua Club official Master Diver Powerpoint presentation.

Contents 1 Safety and emergency procedures 2

Safety in diving 2 Dive planning 2 Risk assessment 3 Incident pit 8 Coping with emergency scenarios 9 Response to an incident 12 Emergency services 13

2 Nitrogen absorption and narcosis 14 Revision of gas laws 14 Nitrogen absorption and elimination 15

Nitrogen narcosis 16 3 Advanced decompression 20 Cause of decompression sickness (DCS) 20 Decompression models 21

Limits of decompression tables and computers 24 Tables v Computers 26

Planning a decompression dive 26 Decompression sickness symptoms 27

Treatment for decompression sickness 28 4 Oxygen, carbon monoxide and carbon dioxide poisoning 32 Oxygen toxicity 32 Carbon dioxide poisoning 35 Carbon monoxide poisoning 36 5 Underwater navigation and search methods 38 Underwater navigation 38 Aids to navigation 38 Use of a compass 41 Underwater search methods 45 6 Basic seamanship 49 Weather 49 Navigation – basic chartwork 51 Tides 53 Buoyage and lights 57

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Navigation 59 Boats 61 Rules of the road 63 Personal safety 65

Anchoring 66 Basic rope work 67 7 Expedition organisation 69 Expedition organiser 69 Selecting a location 70 Advance organisation 70 Organisation on the day 73 Roles and responsibilities 73 Delaying, altering or abandoning a planned dive 76 Chain of command and responsibility 77 8 Compressor operation 79 Basic features of a compressor 79 How a compressor works 82 Compressor log 82 Typical compressor operation 83

Types of compressors 83

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1 Safety and Emergency Procedures

1.1 Safety in Diving Diving activities by their nature contain many elements of risk and danger. Humans are not designed to be submersed in an underwater environment, and rely heavily on complex equipment to ensure safe return to the surface and land. The challenge divers and Instructors face is to ensure that risks associated with diving are managed to reduce the probability of injury to participants. Accidents happen without warning and without requiring any action or contribution from individuals. Incidents happen as the result of action or inaction by an individual. Most dive incidents can be attributed in some way to the action or inaction of someone, usually the diver involved, or their Buddy. It would be reasonable to call most dive events INCIDENTS, and there are very few ACCIDENTS by this definition. The risk of an incident may be reduced by considering the following factors:

• Training and experience of all divers

• Understanding of diving and of incidents themselves

• Dive planning and discipline

• Selection of equipment

• Realistic appraisal of personal limitations

• Common sense

1.2 Dive Planning Whatever the nature of a dive, it will require some form of planning. There are a number of factors which should be considered when planning any dive:

• The dive site and conditions – Where is the site? What type of dive site is it? How will you access the water?

• Number, experience and qualifications of divers and Buddy pairs – linked closely with the dive site, you will need to be aware of the experience level and qualifications. If Trainees or inexperienced divers are involved then the site will require appropriate depths and terrain.

• Equipment available and required.

• Boat space available – many Branches make use of dive charter boats or own smaller dive vessels where space is limited.

• Special interests including wrecks, photography, mixed gas.

• Training required – perhaps the objective of a dive trip is to conduct some training, in which case the nature and level of the training will inform the dive plan.

All dives should be planned, albeit in varying levels of details. Careful planning ensures participating divers have the knowledge, experience and equipment available to execute a dive safely with manageable risk. After considering the above factors, a dive plan may be formed and should consist of at least: the maximum depth, bottom time, maximum duration, approximate route of dive, safety stops, management of any risks and separation procedure. On some dives it may also be

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relevant to specify any planned decompression stops, training or other activities to take place during the dive.

1.3 Risk Assessment Risk assessment is now a familiar term as it exists in many environments including most workplaces. In a diving environment, a risk assessment exists for the same reason as in any other: to minimise danger and prepare for the unexpected. A risk assessment need not be a long and complicated process but should be clear, concise and meaningful to all divers and other participants in the activity. A risk assessment is nothing more than a common sense approach to identifying significant hazards; who is likely to be affected by those hazards; the risks associated with the hazards; what measures will be taken to control the risks – thus reducing the harm to anyone during diving activities; recording the precautions / procedures you have put in place. The assessment needs to be reviewed periodically while the activity is ongoing or whenever there is a significant change in circumstances and any alterations made known to all. Definitions:

• Hazards – are anything that can or may cause harm to divers.

• Risk - is the chance, high or low, that somebody will be harmed by the hazard.

• Control – measures taken to minimise the severity or likelihood of the risk. A risk assessment shouldn’t be seen as a discrete process, but should be incorporated in all aspects of planning. Before choosing a dive site consideration should be given to the divers participating, what level of training they have and what equipment they have. When packing equipment, the diver will consider what they might need for the day ahead including sufficient quantity of air, redundancy, spare equipment. It will be necessary to consider the weather and proximity to supplies. These straightforward activities are already forming the risk assessment by determining the need to avoid hypothermia and hunger respectively. Sensible risk management is about:

• Ensuring that club members, coaches and the public are properly protected.

• Providing overall benefit to society by balancing benefits and risks, with a focus on reducing REAL risks i.e. those which arise most often and those with serious consequences.

• Enabling innovation and learning, not stifling them.

• Ensuring that those who accept risks, manage them responsibly and understand that a failure to manage real risks responsibly is likely to lead to robust action.

• Enabling individuals to understand that as well as the right to protection, they also have to exercise responsibility for their own safety.

Sensible risk management is not about:

• Creating a totally risk-free society.

• Generating useless paperwork mountains.

• Scaring people by exaggeration or publicising trivial risks.

• Stopping important recreational and learning activities where the risks are managed.

• Reducing protection of people from risks that cause real harm and suffering.

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Who Should Perform a Risk Assessments? Normally an appropriate Branch official, Instructor or experienced diver should perform the risk assessment. A risk assessment commences as soon as plans are being made for the activity or expedition so the trip organiser should begin by identifying some of the risks. Recording of Risk Assessments Risk assessments should be recorded in writing, perhaps on a plastic waterproof slate. Whatever the type, they should be clear and concise and should be ‘living’ documents. It is suggested that they should record the five steps listed as shown below. Generic and/or Specific risk assessments should not replace decision-making by the Instructor or dive leader and should not constrain the Instructor from carrying out dynamic risk assessments during training. Frequency of a Risk Assessment A risk assessment should be undertaken for each activity in each specific site, but there is no need to produce a new one each time for a repeat activity at the same venue (although all risk assessments should be reviewed on a regular basis).

Performing a Risk Assessment There are a number of methods of performing a risk assessment. The following is one such method suitable for divers and can form part of the dive planning process.

1. Look for the hazards – consider the hazards above and below the water; consider the

divers involved, their experience and equipment; consider the weather conditions and identify any hazards which might cause harm.

2. Next, identify the risk associated with each hazard. Remember there may be several risks for each hazard.

3. Decide who might be harmed and how – many of the hazards identified in step 1 will affect all of the divers, but there may be some specific risks with different divers due to their inexperience, equipment or training being carried out.

4. Evaluate the risks - decide whether existing precautions are adequate or more should be done to lower the risk. In evaluating the risks, consider both the likelihood and severity.

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• Likelihood of injury is a judgment of the probability of injury occurring and measured on a scale 1-3, where 1 is ‘highly unlikely to occur’; 2 ‘unlikely to occur’; 3 ‘highly possible’

• Severity of injury is where the severity of the potential injury is classified as: 1 ‘minor harm’; 2 ‘harmful’ ; 3 ‘severe risk of injury or death’

The overall risk is simply the likelihood multiplied by the severity.

Slightly Harmful = 1 Harmful = 2 Extremely Harmful = 3

Highly Unlikely = 1 Minimal Risk (1x1 =1) Tolerable Risk (1x2 =2) Moderate Risk ( 1x3 =3)

Unlikely = 2 Tolerable Risk (2x1=2) Moderate Risk(2x2=4) Substantial Risk (2x3=6)

Likely = 3 Moderate Risk (3x1=3) Substantial Risk (3x2=6) Intolerable Risk (3x3=9)

Here, “Tolerable Risk” means slightly higher than minimal, where any necessary measures taken make the remaining risk low. If you cannot get rid of a hazard completely, what can you reasonably do to control the risks so that harm is unlikely?

Record and communicate your findings - a risk assessment should be recorded and not simply contained within an individuals head. An example risk assessment template is available from www.scotsac.com. This template can be photocopied and completed on each dive. When / What Actions are Necessary? Based on the risk evaluation in above, it is often necessary to put in place a range of control measures to manage the risk. The following table indicates some possible actions.

Risk Evaluation Actions Necessary

Minimal / Tolerable

Risk score 1or 2

No additional control measures required; monitor and maintain any measures already in place.

Moderate

Risk score 3 or 4

Can you introduce further control measures to lower the risk? If not, proceed with caution and monitor activities thoroughly.

Substantial

Risk score 6

Diving should not be carried out until the risk can be lowered using, for instance additional safety equipment – personal, on site or on boat; safer access / exit point; more sheltered site.

Intolerable

Risk score 9

Diving should not be considered / continued unless immediate measures can be put in place to reduce risks. Otherwise, abort the planned dive and try to arrange a safer alternative.

5. Review your assessment and revise if necessary – a risk assessment is a live exercise

and should normally be reviewed regularly.

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If it is possible to remove the hazard and risk then this should be the next step, perhaps by amending some factors of your dive plan. If you cannot remove the risk, it should be managed by putting some control measures in place to minimise the risk. If you cannot control the hazard then perhaps the activity should be relocated or aborted. On every dive, divers face a number of potential hazards, but with careful planning, many can be minimised. A risk assessment must form part of every dive plan or training activity.

Example of a Risk Assessment Template Here is an example of a basic risk assessment. The diver has identified a number of hazards relevant to the given dive site. The risks associated with each hazard are listed, along with a control measure which will reduce the probability of the risk occurring. Remember, if the risk cannot be controlled, then further consideration should be given before continuing with the dive.

Risk Assessment Examples Consider the following diving scenarios and see if you can spot some of the hazards and risks, and then consider what controls could be put in place to minimise the risk to divers.

Hazard Risk Likelihood Severity Risk Control

Cold Water Hypothermia 2 2 4 Protective clothing

Low Visibility Separation 1 1 1 Inform/Agree

procedures Wet decks Injury 1 2 2 Rules, Assistance

Running out of

air

Injury/Drowning 1 3 3 Dive planning and

execution

Fishing line Entanglement 1 3 3 Kit streamlined, knife

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Example Risk Assessment Answers

Scenario Hazard Risk Control

1 Surface waves Losing mask

Keep mask on when at surface or

place round neck

Surface Waves Water in face Keep regulator in, and mask on,

when on surface

2 Busy main road Injury/Death Inform divers to stay well in from

road. Park cars in layby away from

road. Do not walk along pavement

with hoods on

3 Moving boat Injury to divers

Falling out

Maintain control of boat and avoid

sudden movement. Divers advised

to hold on whilst boat positions

4 Steep slope at

entry

Diver Injury Carry equipment in batches

Provide assistance for support

5 Wet slipway Falling/slipping Inform divers to avoid dangerous

areas. Walk up beach Dive-Specific Risks Some risks associated with all dives include:

• Air escape

• Contaminated air

• Separation

• Change of conditions

• Equipment failure

• Currents

In addition to generic risks associated with all dives, particular types of dives may have additional risks. Some examples are shown below.

Hazard and Risk Control

Loss of buoyancy control Good buoyancy control, training, experience

Currents Obtaining current information, dive planning

Reef

/ W

all

Div

ing

Going deeper than intended,

perhaps as a result of narcosis

Careful monitoring of depth, time and

narcosis

Entanglement / entrapment Maintain exit point in view, carry knife/cutter,

monitor for lines and nets

Loss of gas supply Careful positioning away from sharp objects,

monitor air supply

Wre

ck D

ivin

g

Low visibility from silt, debris

and darkness

Maintaining close contact, carry torch, good

buoyancy/finning control

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1 minute or more 30 seconds or less 1 minute or more

Minor incidents

emergency

serious

fatal death

panic

fear

Normalactivity

DO NOT FALL IN

1 minute or more 30 seconds or less 1 minute or more

Minor incidents

emergency

serious

fatal death

panic

fear

Normalactivity

DO NOT FALL IN

Tidal influences Obtaining tide information, dive planning,

carrying DSMB

Disorientation Avoid entering enclosed spaces

Damage / injury from broken,

weak or sharp structure

Maintain good buoyancy and appropriate

distance from wreck

Separation from Buddy or

surface cover

Good dive practice; Buddy lines; calm water;

DSMB; boat cover

Visibility Only diving in acceptable visibility

Currents Knowledge of current direction and speed

Entanglement No major obstructions; chart information

Depth Awareness of variable depths

Drift

Div

ing

Temperature / hypothermia Additional thermal protection

Separation from Buddy or

surface cover

Sheltered and calm conditions; good visibility;

torch including backup; illuminated surface

cover Nig

ht

Div

ing

Disorientation Daylight orientation; dive at a familiar site;

Increased risk of DCS High level of experience Thorough planning and monitoring Conditions must be right for dive Depth, time and deco considerations

Effects of Nitrogen Narcosis

Increased awareness of Narcosis Progressive build-up with experienced Buddy Total familiarity and practised to avoid task loading

Deep D

ivin

g

Distance back to surface Sufficient, independent, back-up gas supplies Appropriate equipment for the dive

1.4 The Incident Pit Most problems encountered while diving can be handled. One real danger is that, if problems are not controlled early, they may lead on to more problems. The ‘incident pit theory’ generally goes as follows:

• Problems lead to stress

• Stress leads to more problems

• More problems and more stress leads to PANIC!

• Once panic sets in we have a much slimmer chance of solving a problem. We need break the cycle.

• STOP - BREATHE - THINK – ACT

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1.5 Coping with Emergency Scenarios Despite all good dive planning and comprehensive risk assessments, accidents do still happen in our sport. Divers should train for some adverse situations in order to respond appropriately. The following are examples of emergency scenarios where, with appropriate corrective action, lives may be saved. Regulator failure or air exhaustion Regulator failure may occur due to equipment malfunction or damage sustained during the dive. Many modern regulators lock in an ‘open’ position in the event of failure, delivering a continuous supply air. Air exhaustion may also occur as a result of poor dive planning, carrying insufficient air, over-breathing, failure to adhere to the dive plan or failure to monitor air supply during the dive. Immediate action is required by the diver and includes switching to an alternative air source if available. ScotSAC requires all divers to carry an alternative air source, perhaps in the form of an additional second stage regulator (octopus), or an independent air source such as a pony or independently twin cylinders. The options available will be dependent on the nature of the regulator failure, the divers equipment and the equipment of the Buddy. If an alternative air source is not available to you, you may have to perform a shared ascent to the surface. In order to avoid regulator failure or air exhaustion, divers should maintain their equipment in good order with regular servicing by trained technicians. Loss of air during the dive can be avoided through proper dive planning and execution, ensuring a sufficient supply and reserve of air and, with the supply carefully monitored. Uncontrolled buoyancy A diver’s buoyancy may become uncontrolled as a result of equipment malfunction, ill-fitting equipment, poor buoyancy control or loss of a weight belt. If a diver experiences uncontrolled buoyancy they must react quickly if they are to remedy the situation. Decisions and action need to be taken before the diver’s inertia is overcome and the ascent starts to gain momentum. The faster the diver is ascending, the harder it will be to stay in control. If positive buoyancy has been caused a result of equipment malfunction (for example a stuck inflation valve) a first step would be to disconnect the direct feed hose. In the case of weight belt loss, the diver may be able to fin downwards, or secure position and hold on while the Buddy retrieves the weightbelt and refits it. If the diver is unable to gain a secure stance, or the Buddy cannot find or refit the belt, the diver may have to make a free ascent to the surface. Sticking inflation valves usually result from poorly maintained equipment and a build up of salt in the inflation valve. This is best avoided by regular cleaning and washing equipment after each dive. Loss of a weight belt can be avoided by using correctly fitting equipment.

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Fainting or lack of response to signals If a diver does not respond to routine signals during a dive (especially an ‘OK’ signal) the signal should be repeated. If there is still no response, the Buddy should move in and investigate. The victim may be unconscious, ‘narked’, or experiencing other difficulties. Once the situation has been assessed and it is established that the casualty requires assistance, they should be removed from danger in a safe and controlled manner by rescue to the surface. The rescuer should have regard to their own safety. Rescue techniques are covered in Sport Diver lecture 7. Trapped diver A diver carries a finite supply of air. If they are injured, trapped or in distress their breathing rate will increase and their breathing gas will be depleted faster. Attempts should be made to reassure and calm the trapped diver, and a quick assessment of possibilities of release should be carried out if safe to do so. If safe rescue cannot be effected, it is imperative that assistance is alerted on the surface. High pressure air escape This usually occurs from a burst hose or ‘O’ ring. If this happens and it is still possible to breathe from the regulator, the diver should ascend to the surface as safely as the air supply will allow. If the air supply is depleted prior to reaching the surface, an assisted ascent with their Buddy should be attempted. Separated or missing Divers If a diver becomes separated from their Buddy, they should attempt to regain contact by turning round slowly twice, looking up and down, and shining a torch if available. If after a short time, there is no sign of the Buddy, a slow ascent to the surface should be conducted. On deep dives, the agreed separation procedure may vary. If contact is not made with the Buddy on the surface after a few minutes, shore or boat cover should be alerted. If divers become separated on the surface from their boat, they should try to remain together, ensuring their BCDs are inflated and dumping weightbelts if necessary. If drifting in a strong current, they should not attempt to swim against this, but use any surface location aids they have available. Warning signs of a diver in difficulty What are the indications that a diver is in difficulty, and how can they be dealt with? The following are some possible signs that may be observed in a dive Buddy.

• DISTRESS SIGNAL - A fist waved from side to side in front of the victim’s face, or with an extended arm above the head on the surface. This is a direct call for emergency help and must be answered immediately.

• “OUT OF AIR” SIGNAL - A chopping motion with a flat, open hand towards the victim’s throat, or straight fingers towards the victim’s mouth. The diver finds out he has no air when he exhales and then try to inhale but get nothing. A diver who is out of air needs instant help: respond at once.

• LACK OF RESPONSE TO SIGNALS - If a diver does not respond to any of your routine signals during a dive (esp.

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‘OK’ signal) the signal should be repeated and if there is still no response the Buddy should move in and investigate. The victim may be unconscious, ‘narked’, or experiencing other difficulties. Find out.

• SIGNS OF APPREHENSION - If it is felt that a diver in the water looks, or acts, as if they are worried or scared, move in and investigate.

• CONSTANT CHECKING OF GAUGES - All divers should check their air, dive time, and depth during a dive. If a diver seems to be checking excessively, or obsessively, it can be a sign of apprehension or concern about themselves, their equipment, or the dive plan. Move in and investigate: are they are OK?

• ORIENTATED TOWARDS THE SURFACE - A relaxed diver will tend to adopt a flat position in the water or orient themselves slightly towards the sea bed. If a diver continually adopts a body position oriented towards the surface this can sometimes a sign of apprehension or unease. Move in and investigate.

• UNUSUAL BEHAVIOUR - Any unusual behaviour by a diver should be investigated. There may, or may not, be a problem. Move in and investigate.

• PANIC - If a diver is in extreme distress they may become very anxious and agitated and they may panic. A panicking diver is a difficult situation to deal with. They are not in control and may shoot to the surface, try to discard equipment, or otherwise endanger themselves. However, it may not be easy to approach safely and take hold of a panicking diver. Panic is a very serious situation which demands both a rapid and a carefully considered response.

• EQUIPMENT PROBLEMS – Some equipment problems may be minor and relatively non-life-threatening. However, even minor problems such as a broken fin strap may escalate to a significant incident if buoyancy is lost as a result. Offer assistance if possible. If the problem cannot be resolved, then a controlled ascent to the surface should be performed.

Avoid Becoming a Victim Incidents happen, even to the best trained, prepared and equipped divers. There are, however, ways to minimise the chances of becoming a victim.

• DEVELOP PERSONAL TRAINING. Structured training is designed to develop a divers skills and experience, and your ability to cope with many different situations. Practise the skills you have learned (diving and rescue) regularly.

• MAINTENANCE and CHECKING OF EQUIPMENT – Personal equipment should be in good working order and be properly maintained, cleaned and serviced. Salt build up is a common cause of failure in inflation systems and valves; dirt and sand can jam dump valves open.

• CORRECT WEIGHTING – is important for a safe and comfortable dive. The addition of new equipment such as a pony bottle or new undersuit may require an adjustment in weight. Weight requirements in salt water are greater than fresh water, so it is important to adjust weight accordingly if switching between these environments.

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• AWARENESS OF AIR CONSUMPTION AND DURATION – There are many factors which can affect the air consumption of a diver. It is therefore important to regularly monitor air reserves and adjust the dive plan if required.

• CONSERVATIVE DIVE PLANNING –Dive planning should take into account the divers training, experience, recent diving, and physical and mental condition.

Make a dive plan of the entry and exit points, route and navigation, maximum depth and planned time. Ensure that the Buddy is aware of the dive plan and that it is known by the divers giving cover. This will be vital information for deciding early if divers are missing, or over time, and responding in the most appropriate way.

If unsure about the sea conditions before a dive, or if conditions change during a dive, the dive can always be aborted. The reef, wall, or wreck will still be there another day. Do not be worried about doing this: it is far better to be safe and cautious, than an adventurous casualty.

• BE VISIBLE ON THE SURFACE – Divers are difficult to spot on the surface of the water, especially when wearing dark colours and the sea state is anything but flat calm. Bright colours on hoods and upper body along with surface location aids can increase the chance of being located at sea. Dive torches and strobes can also be useful for surface location, even in daylight.

Audible signals can be very useful, but shouting can be surprisingly weak at sea. Make use of whistles or, better still, there are very powerful air horns powered from the BCD direct feed. Some divers are carrying more technical aids to surface location such as personal flares, smoke flares, and the most recent Electronic Position Indicating Rescue Beacons (EPIRBS) are starting to appear.

Perhaps the best aid to surface detection is the combination of good dive planning, good discipline, and good navigation which allows the diver to surface when they said they would and where they planned to be.

• USE OF BOAT COVER IF APPROPRIATE - If diving with a boat, or boats, phase diver entry appropriately. Diving in two waves of divers leaving people in the boat to pick the divers up as they surface provides important back-up and surface cover. It is much easier for a boat to come to a diver than for a diver swim to a boat.

1.6 Response to an incident If an incident occurs the dive party, and most often the dive pair, in the water must deal with it.

• SELF-HELP : Building redundancy into equipment e.g. redundant air supply, backup torch, computer, spare mask and fin straps allows divers to help themselves in the event of a minor incident. If an incident happens, they can often be able to supportits resolution without the active intervention of their Buddy.

• RESCUE : It is essential in order to make this possible that the Buddy diving system works and that divers continue to practise and refine their rescue techniques.

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• RECORD THE INCIDENT : ScotSAC requires that all diving incidents should be recorded and reported in order to allow a picture of the types of incidents to be developed. Incidents should be recorded on the ScotSAC incident reporting form, available from www.scotsac.com. Record details while fresh in participants’ minds.

• LEARN FROM THE INCIDENT : Talk about incidents; do not be ashamed of them: they happen. Try to discuss why incidents happened, what went wrong, how it was resolved and how it may be prevented in the future. We do not all have to make the same mistakes in order to learn; we can learn from the actions and experience of other divers.

1.7 Emergency Services HM Coastguard is the first point of contact for diving incidents at sea or the coast. All areas of the UK coastline are served by the Coastguard as an emergency service, but accessing remote areas may take some time. It is therefore vital to alert the Coastguard to any potential problems as early as possible. At the coast phone 999 or 112 - ask for ‘COASTGUARD’. If at sea use VHF radio on channel 16, making a ‘Mayday’ or ‘Pan Pan’ call. If you have travelled from the dive location and require assistance related to a suspected diving injury or illness, contact the National Hyperbaric Centre on 0845 408 6008 (Scotland) or 07831 151523 (England). When contacting any emergency service, be ready to give clear and accurate information including

– Vessel identity, if applicable

– Location

– Type of incident

– Number of people involved

– Contact details etc

– Type of assistance required Incident Reporting If an incident does happen, it must be reported appropriately to ensure others may learn from it and future events. There may also be legal implications of the incident and recording the event whilst fresh in participants’ minds is crucial. Incident reporting is confidential. Within ScotSAC, incidents should be reported via the BDO on the incident reporting form. These reports are reviewed by the National Diving Council to monitor trends in incidents. Summaries of the incidents (with personal and identified information removed) are compiled by the British Sub-Aqua Club on behalf of all diving agencies in the UK in order that a national picture can be analysed. Feedback from incidents helps maintain the safety record of the sport Summary Diving has a very good safety record. Safety doesn’t happen by accident. Ensure dives are planned within the experience of all divers involved. Plan the dive and carry out a Risk Assessment to prevent incidents and promote safe diving practices.

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2 Nitrogen Absorption and Narcosis

2.1 Introduction This lecture covers the absorption of nitrogen and effect of increased partial pressure of nitrogen on the body. 2.2 Revision of Gas Laws Two gas laws are relevant to the consideration of the effects of nitrogen on the body. Dalton’s Law states “The partial pressure (pp) of a gas in a gas mixture is the part of the total pressure of the gases that is contributed to by that gas”.

OxygenNitrogenOxygenNitrogen

Air at 1 bar

0.21 bar O20.21 bar O2

0.79 bar N20.79 bar N2

1 bar Air1 bar Air

Air at 2 bar

2 bar Air2 bar Air

0.42 bar O20.42 bar O2

1.58 bar N21.58 bar N2

At 1 bar, air is composed of approximately 21% oxygen and 79% nitrogen. The partial pressure at 1 bar is therefore composed of 0.21 bar oxygen and 0.79 bar nitrogen. At 2 bar, the proportion of oxygen and nitrogen in the air remains the same, so the partial pressure of oxygen doubles to 0.42 bar, nitrogen to 1.58 bar. Henry’s Law states “At a constant temperature, the amount of gas that will dissolve in a liquid is proportional to the partial pressure of the gas over the liquid”. At depth, gas will dissolve into a diver’s blood in proportion to the partial pressure of the gas in their lungs:

Tissues LungOxygenNitrogen

Surfacepp of dissolved gases in blood and tissues equal to surface pp

Tissues LungOxygenNitrogenOxygenNitrogen

Surfacepp of dissolved gases in blood and tissues equal to surface pp

Diver descends to 10m, pp of gases in lungs increases, gas diffuses to tissues

Diver descends to 10m, pp of gases in lungs increases, gas diffuses to tissues

pp of dissolved gases in blood and tissues equal to pp at 10m

pp of dissolved gases in blood and tissues equal to pp at 10m

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2.3 Nitrogen Absorption and

Elimination Nitrogen Absorption Anyone living at sea level for some time will be saturated with nitrogen for that partial pressure (79% of 1 bar=0.79 bar). On a dive, the partial pressure of nitrogen in breathing gas will increase with depth (Dalton’s Law) and the nitrogen in a diver’s tissues will eventually rise until it approaches saturation (Henry’s Law).

Half Times The rate of uptake of nitrogen can be better understood through the concept of ‘half times’. A tissue which takes 5 minutes to take on half the difference in partial pressure is said to have a half time of 5 minutes. Within 10 minutes it will have taken on 75% etc as illustrated below. After 6 half times, a tissue can be considered to be fully saturated. Movement of Nitrogen in the Body The difference in partial pressures provides a driving force that determines the rate at which gas dissolves into blood. Nitrogen passes from solution in the blood to the surrounding tissues and the blood returns to the lungs with a lower concentration of nitrogen than it had when it left the lungs. It then picks up more nitrogen to transfer to the tissues. Initially, the difference in partial pressures is large so nitrogen starts to dissolve rapidly in the blood. As the amount of nitrogen in the blood and body rises, the difference in partial pressures lessens, and nitrogen dissolves more slowly in the blood. Solubility of Nitrogen in the Body The amount of gas which can dissolve in a tissue is also dependent on the solubility of gas in the tissue. Body cells are composed largely of water and a small amount of fat. Different tissues have different amounts of water and fat in them. Nitrogen is much more soluble in fat than it is in water, therefore tissues containing a lot of fat will take up more nitrogen than those with less fat. Divers with a higher body mass index will take on proportionally more nitrogen during a dive.

Uptake of Nitrogen in tissues

0

1

2

3

4

-2 0 1 2 3 4 5

Time in Hoursp

p o

f d

iss

olv

ed

Nit

rog

en

(ba

r)

Start of

Dive

Saturation

Attained

Uptake of Nitrogen in tissues

0

1

2

3

4

-2 0 1 2 3 4 5

Time in Hoursp

p o

f d

iss

olv

ed

Nit

rog

en

(ba

r)

Start of

Dive

Saturation

Attained

Time since start of dive

0 5 10 15 20 25 30

Time since start of dive

0 5 10 15 20 25 30

Time since start of dive

0 5 10 15 20 25 30

pp at start of dive

Max pp for depth

pp at start of dive

Max pp for depth

Uptake of nitrogen in tissue with 5 minute half time (nominal units)

At surface pressure

At 10m

16

The rate at which tissues take up nitrogen will also depend on the rate of blood flow to the tissue (PERFUSION).The brain, kidneys and heart all have a large blood supply and will saturate with nitrogen quickly (fast tissues). Other tissues such as cartilage, tendons and fat stores have a poor blood supply so will take longer to become saturated (slow tissues). This will be important to the consideration of decompression models and decompression sickness, discussed in chapter 3. Release of Nitrogen As a diver returns to the surface the ambient pressure of the breathing gas decreases and the pp of nitrogen in the tissues becomes greater than the pp of nitrogen being breathed. The body seeks to rid itself of the excess nitrogen in the tissues by pushing it back out into the blood and out through the lungs. Fast tissues will release nitrogen more quickly than slow tissues. Controlling this process through dive planning (including decompression and safety stops) is critical in the avoidance of Decompression Sickness (DCS). 2.4 Nitrogen Narcosis Cause of Nitrogen Narcosis Nitrogen narcosis, more correctly know as Inert Gas Narcosis (IGN), is the name given to the clinical syndrome characterised by the impairment of intellectual faculties, motor control, and changes in mood and behaviour of a diver breathing gas at an increased pressure. Medically, nitrogen narcosis is described as the impending anaesthesia of the diver. Divers often refer to nitrogen narcosis by a variety of names such as ‘the Narks’, ‘Depth Intoxication’ or the ‘Rapture of the Deep’. Nitrogen narcosis only became an issue when the effects on working divers began to take a toll on lives. Nitrogen narcosis was widely recognised in caisson works and Royal Navy divers; however, only after several losses in deep diving did the navy carry out investigation into the causes and clinical effects of nitrogen narcosis. Nitrogen narcosis was not attributed to Nitrogen until 1935 when Benke replaced nitrogen with helium and noted no adverse symptoms. Nitrogen is an inert, non-reactive gas, which at low partial pressures has no effect upon the body. During diving, when nitrogen is breathed at higher partial pressures, it acts as a narcotic in a manner similar to alcohol. It operates as an anaesthetic and impairs the transmission of impulses between nerve endings within the brain. Unlike DCS, nitrogen narcosis is not caused by nitrogen release; the effects reduce immediately on ascent. Effects of Nitrogen Narcosis The effects of nitrogen narcosis are unavoidable on deep dives using air. The threshold at which the effects are obvious is generally regarded as a pp of nitrogen of 3.0 Bar, which equates to around 30m. In reality, however, any increase in the pp of nitrogen has an effect

Uptake of Nitrogen in fast and slow

tissues

0

20

40

60

80

100

0 1 2 3 4 5

Time (hours)

% S

atu

rati

on

Fast Tissue

Slow Tissue

17

and many divers will show some of the effects of nitrogen narcosis from even shallower depths. An individual diver’s response to nitrogen narcosis will also vary from dive to dive. On one dive they may feel fine at 40m but on the next dive they may feel obviously ‘narked’ at 30m.These individual differences make it hard to develop hard and fast rules; however:

• Some divers will be affected by nitrogen narcosis at depths shallower than 40m.

• Beyond 40m ALL air divers will suffer from nitrogen narcosis, although they may still be able to function adequately and safely.

• At 50m the effects of nitrogen narcosis are more obvious, at least to an observer; the diver may not be aware of it and think they feel fine.

• Beyond 60m nitrogen narcosis is a real hazard to the diver’s safety.

• Beyond 80m there is a real chance of collapse and unconsciousness.

• The symptoms disappear as the diver ascends to a lower pp of nitrogen.

• One of the effects is loss of short-term memory.

Symptoms of Nitrogen Narcosis As the diver descends and the pp of nitrogen increases the diver will experience a range of different symptoms. Early symptoms with relatively, low risk:

• Initial feelings of well-being, self-confidence or light-headedness.

• Feelings of detachment.

• Deterioration in judgement and

0

10

20

30

40

50

60

70

80

90

Depth (m)

0

10

20

30

40

50

60

70

80

90

Depth (m)

0

10

20

30

40

50

60

70

80

90

Depth (m)

0

10

20

30

40

50

60

70

80

90

Depth (m)

Some divers experience slight narcosis

More divers experience narcosis

Narcosis obvious in most divers

Narcosis affects performance

Narcosis becomes a hazard to safety

Narcosis causes collapse and unconsciousness

18

• Partial loss of fine control One of the dangerous aspects of nitrogen narcosis is the feeling of well-being and contentment that can sometimes be experienced. Feeling good about the dive, the diver may become engrossed with enjoying the feeling and not identify it as a symptom of nitrogen narcosis. Avoiding action to prevent nitrogen narcosis becoming worse may not be taken in time. Progressive symptoms with relatively higher risk:

• Slowing of the ability to react to signals or situations.

• Less attention paid to personal safety

• Increasing loss of manual dexterity.

• Deterioration in the power of concentration and decision-making

• Task fixation: a diver may be so intent on trying to read their contents gauge that they do not notice themselves sinking too deep.

• Increasing anxiety. Serious symptoms with very high risk include:

• Depression

• Loss of clear thinking

• Loss of co-ordination

• Bizarre behaviour

• Collapse and unconsciousness. Coping with Nitrogen Narcosis Fortunately, the treatment for nitrogen narcosis, if recognised, is very simple. Reduce the pp of nitrogen in the breathing gas and the effects of the nitrogen narcosis will be reduced. Ascend far enough and the symptoms will go away. There are no serious after-effects for the diver other than sometimes an inability to remember what they did when suffering from nitrogen narcosis. nitrox divers use a gas mixture with a higher pp of oxygen and a lower pp of nitrogen. This creates less nitrogen narcosis for any specific depth, and nitrox divers often report that they feel less fatigued at the end of a dive when compared to the same dive on air. In trimix diving, helium is introduced to the breathing gas and the proportion of nitrogen and / or oxygen reduced to allow the gas to be used at greater depths. This limits the effects of nitrogen narcosis. ‘Technical’ divers who descend on air and then switch at depth to ‘a bottom gas’ with a much lower pp of nitrogen report that the symptoms of nitrogen narcosis disappear after a few breaths of the lower pp nitrogen ‘bottom gas’. It takes about 15-16 breath cycles to completely change the gas configuration in the brain and makes the use of a ‘travel gas’ for descent unhelpful in the depth ranges we are covering in this course. The only way to avoid nitrogen narcosis is to not dive deep on air, or other gases with a high pp of nitrogen. Divers seem to be able to cope better with the effects of nitrogen narcosis and function more effectively if they have often worked at depth, or have experienced nitrogen narcosis before. Acclimatisation cannot make narcosis disappear, but with the right experience and attitude a diver can learn to work effectively within it. A good test to check if a diver is ‘narked’ is to show them a number of fingers and they have to respond by showing one more than that number. The accuracy and the speed of response can be very telling.

19

Task-loading problems with nitrogen narcosis can be offset by forward planning to reduce decision making at depth. The diver’s ability to make decisions and to formulate a dive plan is reduced under the influence of nitrogen narcosis. It is, therefore, useful to make as many decisions as possible before the dive and take a written copy of the dive plan (depth, time, decompression and air requirements) down on a slate. Similarly, prior planning to work out contingency plans for other depth/time profiles are strongly recommended. Strong motivation and concentration on the dive plan and the task in hand will help to counter the effects of nitrogen narcosis, especially in the early stages.

20

3 Advanced Decompression 3.1 Introduction This lecture describes the physical cause of decompression sickness in detail. The principle of decompression models, their limitations and use in the formation of dive tables and computers is explored. Symptoms and treatment of decompression sickness are also covered. 3.2 Cause of Decompression Sickness (DCS) DCS is caused by the release of nitrogen following lowering of the ambient pressure causing the growth of bubbles in the bloodstream that reach a size that causes them to lodge or stick in body tissues. As discussed in lecture 2, nitrogen accumulates in the body tissues during a dive. The amount of nitrogen in any given tissue will depend on the length and depth of the dive, the percentage body fat of the tissue and the blood supply to it. On ascent, the blood is the first tissue to exchange this excess nitrogen through the alveoli of the lungs and the re-circulated blood has a lower pp of nitrogen than the surrounding tissues. This means the tissues through which the blood passes have a higher pp of nitrogen than the blood and so they diffuse gas into the blood in order to regain equilibrium. While most nitrogen is released as micro-bubbles, a small amount is carried in solution in the blood. With a VERY slow ascent it is theoretically possible to avoid bubbles and transport all of the nitrogen as solution. In practice, this is extremely slow and unlikely to be achievable. It is thought that micro-bubbles form as a result of gas micronuclei – small gas pockets present in tissue walls. Nitrogen diffuses into the micronuclei causing expansion. A small bubble then breaks free and travels through veins into the lungs, where it diffuses into the aveoli. Microbubbles may combine to form ‘silent’ bubbles, which are detectable by Doppler Ultrasound. These silent bubbles may sometimes grow and combine, forming larger bubbles which will expand on ascent and can lead to the development of decompression sickness.

Vein

Tissue

Gas micronuclei

Microbubble

Silent bubble

Larger bubble

Vein

Tissue

Gas micronuclei

Microbubble

Silent bubble

Larger bubble

The pressure difference between inspired nitrogen and that dissolved in tissues must be kept within certain limits to prevent larger bubbles forming in the blood stream. This limit is known as the Critical Ratio. Critical Ratios vary across tissue type, with fast tissues having significantly higher ratios than slower tissues.

21

3.3 Decompression Models Both decompression tables and computers utilise theoretical decompression models to estimate the amount of excess nitrogen held in a diver’s tissues for a given depth and duration of dive. This information is then used to estimate whether a direct ascent to the surface (i.e. a no-decompression dive) can be carried out. Where this is not possible, decompression stops are used as a means of reducing the residual nitrogen in the tissues to a level where ascent to the surface falls within acceptable limits. Tissue Compartments Decompression models use the concept of tissue compartments to estimate the amount of excess nitrogen held within the various types of body tissues for a given duration and depth of dive. A tissue compartment is based on the idea of “Half Times”. This is the time it takes for the tissue to absorb half of the remaining gas needed to reach saturation. For instance, a “5 Minute” compartment is 50% saturated in the first 5 minutes. It is 75% saturated after 10 minutes and so on. By six half times, the tissue is considered saturated. As discussed in lecture 2, different tissues take on nitrogen at different rates, so decompression tables use multiple compartments to model the body. For Buhlmann tables, 16 compartments, ranging in half times from 4-635 minutes, are used.

0 20 40 60 80

10

0

12

0

5 min10 min20 min

0

50

100

%

Sa

tura

tio

n

Mins

Tissue half times

5 min

10 min

20 min

M-Values Decompression models assume that during release of nitrogen on ascent, some level of bubble formation can be tolerated in the tissues. The models reflect this by using a system known as M-values. M-values are the maximum pressure the tissue can tolerate before bubbles capable of causing DCS occur and are a refined version of the critical ratio idea.

22

Different tissue compartments have different M values. The M-value is an empirical concept based on experimental observations and mathematical models; it is not a known fact like the Gas Laws. Divers should appreciate this for the simple reason that as the dive profile pushes them closer to the M-Value, the more likely they are to suffer DCS. Mo (‘M nought’) is the maximum gas tension that can be tolerated at the surface. Exceeding this value will entail staged decompression stops. When a tissue compartment reaches its Mo value, ascent to the surface without a decompression stop is no longer safe. M Values and Tissue Loading The following examples show the concept of tissue loading and M values in more detail. In the first example, a short deep dive is undertaken. None of the tissue compartments have reached their Mo value, so it is safe to ascend to the surface with only a safety stop.

A slightly longer dive to the same depth shows that the 5 minute tissue compartment has now reached its Mo value, and decompression stops will now be required.

Tis

su

e p

res

su

re (

ms

w)

5 10 20 40 80 120Compartment half time

Tissue Load

No stop load left

Mo value

Nitrogen absorption for 10 mins @ 35m

Tis

su

e p

res

su

re (

ms

w)

5 10 20 40 80 120Compartment half time

Tissue Load

No stop load left

Mo value

Nitrogen absorption for 10 mins @ 35m

Tis

su

e P

res

su

re (

ms

w)

5 10 20 40 80 120

Compartment half time

Tissue Load

No stop load left

Mo value

Nitrogen absorption for 15 mins @ 35m

Tis

su

e P

res

su

re (

ms

w)

5 10 20 40 80 120

Compartment half time

Tissue Load

No stop load left

Mo value

Nitrogen absorption for 15 mins @ 35m

23

On deep dives, it tends to the fast tissue compartments (with shorter half times) which govern decompression requirements. On longer shallower dives, the maximum pressure that can load into any compartment is relatively low. Even after saturating, the load in fast tissues will be less than the M-value, hence the slow tissues will govern no-stop decompression limits as they have lower M-values than the fast tissues. In the example below, it is the 20minute compartment which determines the no-stop time.

Where repetitive dives are undertaken, the residual nitrogen levels present in tissues from the previous dive will affect the tissues which control decompression requirements. Whilst the residual nitrogen in the fastest tissues will be eliminated during a surface interval, medium and slow tissues will retain an element of residual nitrogen. The slowest tissue compartments, which can have a half time of up to 10 hours, will not accumulate significant amounts of nitrogen on a single dive. However, where repetitive dives are undertaken over a period of days or weeks, the residual nitrogen levels in these compartments build up and can have a significant effect on decompression requirements – nitrogen in these compartments can take 2-3 days to return to normal levels.

Tis

su

e p

res

su

re (

ms

w)

5 10 20 40 80 120Compartment half time

Tissue Load

No stop load left

Mo value

Nitrogen absorption for 30 mins @ 25m

Tis

su

e p

res

su

re (

ms

w)

5 10 20 40 80 120Compartment half time

Tissue Load

No stop load left

Mo value

Nitrogen absorption for 30 mins @ 25m

Tis

su

e p

res

su

re (

ms

w)

5 10 20 40 80 120Compartment half time

Nitrogen absorption for 15 mins @ 35m

Tis

su

e p

res

su

re (

ms

w)

5 10 20 40 80 120Compartment half time

Nitrogen absorption for 15 mins @ 35m

Tis

su

e p

res

su

re (

ms

w)

5 10 20 40 80 120Compartment half time

Residual nitrogen – 1hr surface int

Tis

su

e p

res

su

re (

ms

w)

5 10 20 40 80 120Compartment half time

Residual nitrogen – 1hr surface int

Tis

su

e p

res

su

re (

ms

w)

5 10 20 40 80 120Compartment half time

2nd Dive 15 mins @ 35m

Tis

su

e p

res

su

re (

ms

w)

5 10 20 40 80 120Compartment half time

2nd Dive 15 mins @ 35m

24

BUBBLE COUNT FOLLOWING

A 25 MINUTE DIVE TO 30 METRES

BUBBLE

COUNT 120

110

100

90

80

70

60

50

40

30

20

10

0 0 10 20 30 40 50 60 70 80 90 100 110 120

SURFACE INTERVAL IN MINUTES

Bubble Count with NO STOPS

Bubble Count with 2 Min @ 3 Metres

Bubble Count with 4 Min @ 3 Metres

1 Min @ 6 Metres

Pilmatis (1975)

Decompression Stops No stop dives, where the diver surfaces without carrying out a safety stop, are not endorsed by the ScotSAC. For all dives ScotSAC advises a 1minute safety stop at 3m. The one minute stop has two distinct benefits: controlling buoyancy at a point where pressure change is greatest, and also to reduce the number of silent bubbles in the bloodstream. On longer or deeper dives, the body absorbs more nitrogen than it can release safely on a normal ascent. Decompression stops at set depths and times are required to ascend safely. 3.4 Limits of decompression tables and computers There are many decompression tables, systems and even wheels in use worldwide. The ScotSAC recommend Bulhmann ZL-16A decompression tables. The limits set within these tables must not be exceeded. No decompression tables or computers exist that will protect you against all the risks of decompression illness. All accept that a very small percentage of divers will experience DCS within the limits prescribed by individual tables and computers. This is due to the wide variation in human physiology and factors affecting decompression in a diver. Tables also assume a level of control in depth, duration and ascent rate of a dive that is rarely achieved by recreational divers, so we must recognise these factors and modify our dive profiles to limit our risks. These factors can be categorised as either physiological or physical factors. Physiological Modifying Factors Dive tables are generally formulated with an ‘average’ diver in mind. The age, body fat content and fitness of a diver all have a marked effect on the risk of a diver developing DCS. There is a direct relationship between these factors and DCS - put simply, the older, more overweight and less fit the diver is, the greater the risk of DCS within the limits of a decompression table. Long-term injury and illness can also increase the risk of DCS. Another modifier that often remains latent until a diver experiences an unexplained DCS incident is a PFO. PFO stands for patent foramen ovale and is more commonly know as a “hole in the heart”. An individual with a PFO will live quite happily with it until they either dive or fly to high altitudes. In a normal heart, the bubbles will pass from the right side of the heart to the lungs, where they would be released and then oxygenated blood returned to the left

25

side of the heart. In the case of a PFO, the bubbles in the right side of the heart and pass directly into the circulation on the left side, and pass to the vital structures around the body, so increasing the risk of DCS. There is an inverse relationship between aerobic fitness (cardiovascular) and risk of DCS i.e. the fitter the diver is the less likely they are to develop DCS. Divers should be encouraged to maintain or improve their level of fitness or adopt a more conservative approach to diving within the limits of the decompression tables. These are broad physiological modifiers that tend to affect a diver over a long period of time; however, there are modifying factors that vary from day to day. Dehydration, fatigue, drugs and alcohol intake, short-term illness or injury, increased carbon dioxide and low temperatures all increase the risks of DCS. Dives should only be undertaken if the diver is well rested and well hydrated. Both of these factors affect the perfusion of nitrogen within the tissues of the body and hence the way the body decompresses. Divers should note that both the use of alcohol and some drugs also dehydrate the body. The body may take upwards of 24 hours to recover from dehydration and moderate alcohol consumption. Use of recreational drugs is considered a complete bar to diving. The relationship between temperature and decompression are complex; it affects the rate of perfusion of nitrogen (high temperature = high blood flow) and the solubility of nitrogen in the blood (low temperature = more soluble). In Scottish diving, typically, a diver would be warm on descent and cool throughout the dive; thus, as the diver cools, their ability to eliminate the nitrogen is lessened and the risk of DCS increases. Divers must use thermal protection to ensure they maintain their body temperature. Physical Modifying Factors Dive tables assume a square profile dive i.e. a rapid descent to depth, followed by time spent at that depth, followed by a controlled ascent to the surface. During the dive the diver is assumed not be exerting themselves unduly. The main modifying factors for sports divers are physical exertion, poor dive profile, altitude and multiple day diving. Physical exertion whilst diving has a major effect on the rate a tissue saturates with nitrogen. This is due to the increased blood flow to the muscles carrying out the work and hence the increased supply of nitrogen to the tissue. The increased nitrogen saturation will not be catered for in a standard decompression table, so the diver must be more conservative in their use of the table. Poor dive profiles include “saw-tooth” and “reverse profile” diving. Both of these promote the formation of nitrogen bubbles during the dive; once formed, these bubbles will not dissipate in the manner predicted by the tables and will increase the risk of DCS. Altitude also has a bearing on the relevance of tables. Most diving takes place at sea level where atmospheric pressure is at its greatest. When diving is undertaken at an altitude greater than 300m the ScotSAC Bulhmann tables are no longer suitable for use, due to the reduction in atmospheric pressure. Similarly, travelling to altitude after diving can also provoke DCS by producing or expanding silent bubbles within the bloodstream. Travelling to altitude can be as dramatic as air travel, or as seemingly trivial as driving home across a high-level road after a dive. Before flying a minimum surface interval of 12hrs is recommended for single dives. A minimum of 24hrs is recommended after a multiple series of dives. Before travelling home on a high-level road, a surface interval in excess of two hours should be observed.

26

Repetitive diving over a number of days is proven to produce an increased risk of DCS within the limits of Decompression Tables. Repetitive diving may lead to a situation where the diver does not de-saturate between dives, even overnight, leading to a build-up of residual nitrogen in the body which dive tables may not take full account of. For this reason, divers are recommended to take a break from diving every fourth day during multiple day diving (e.g. diving holidays) to limit the build up of these silent bubbles within their bodies. 3.5 Tables v Computers Tables are considered by some to be more conservative than dive computers. Tables were originally developed for commercial use and assume square profile dives where all the bottom time is spent at the maximum depth. Obviously, very few sport dives are true square profile dives and generally involve multi-level profiles, therefore tables err on the side of caution. However, tables may require recalculation at depth if the dive plan changes, possibly leading to errors and task overloading. Dive computers continually recalculate the theoretical nitrogen uptake and decompression requirements, more accurately reflecting the actual situation. However, unless used in a considered manner, they also encourage the user to get closer to the decompression limits, leaving less margin for error. Whilst both these views are true, it is generally not as clear cut as this. Many computers can be programmed with a safety margin. In addition, computers tend to deal with excess nitrogen in a more realistic manner. When undertaking multiple dives over several days, a computer is likely to indicate the presence of residual nitrogen for extended periods, whereas a dive table is likely to indicate that the diver is clear of excess nitrogen after 12 hours. It is important to remember that neither tables nor computer will accurately reflect a diver’s exact body response, so erring on the side of caution is always to be recommended. 3.6 Planning a Decompression Dive Decompression diving requires a degree of planning, resources and discipline which is not normally required on a 15 - 20m club dive. It also greatly increases the chances of an incident and a bend. In addition to normal dive planning procedures, there are additional considerations which should be taken into account if decompression dives are planned:

• Appropriateness of site – can decompression stops be carried out safely?

• depth and time – are decompression stops excessive?

• gas and cylinders requirements

• shot line

• dive lights

• decompression tables and slates

• reels and line and delayed SMB

• redundant air supplies and regulators

• protection against cold

• standby divers

• access to site in an emergency If diving is planned at altitude, different tables and computing modes are required to cope with the decrease in surface pressure. 3.7 Decompression Sickness Symptoms (source Scottish Diving Medicine)

27

DCS can cause a variety of symptoms in various parts of the body. All should be taken seriously and treated as DCS if in any doubt. General signs

• Nausea

• Weakness

• Fatigue

Skin

• Itching

• Generalised rash

• Lumps

• Skin marbling (Cutis marmorata marbling) - serious sign

• Crackling feeling (subcutaneous emphysema) - not usually around collarbone

• Musculoskeletal (muscles and joints)

• Joint or muscle discomfort and / or pain ("bends")

• Limitation of limb movement

• Crunching sound in joint

Gastrointestinal (stomach and bowel)

• Nausea, vomiting

• Abdominal cramps, diarrhoea Cardiorespiratory (heart and lungs)

• Coughing

• Chest pain made worse on inspiration

• Increase in breathing rate (Tachypnoea)

Neurological (cerebrum, cerebellum, spinal cord, inner ear and peripheral nerves)

• Headache

• Confusion

• Memory loss

• Tremors

• Visual disturbance (scotoma)

• Involuntary eye movement (nystagmus)

28

• Lack of co-ordination (ataxia)

• Numbness or altered sensation

• Pins and needles (paresthesia)

• Urinary retention

• Ringing sound in ears (tinnitus)

• Hearing loss

• Dizziness, loss of balance (vertigo)

• Partial or full paralysis of lower limbs (paraparesis / paraplegia)

• Unconsciousness The onset of decompression sickness in air diving always occurs after surfacing from depth. The time-scale for the onset of DCS can vary but in general 50% of symptoms will occur with in an hour and 90% within a day. That is not to say the diver will actually admit the symptoms in this time-scale, as denial is often a problem with DCS. Divers often feel tired after a dive, more so if repeat diving. The fatigue, lethargy and generally feeling unwell associated with DCS is more than the normal levels of fatigue. nitrox divers report that diving on nitrox reduces the degree of fatigue felt after a dive, although if they have dived to the no-stop limits this might be more psychosomatic than fact. Fatigue symptoms usually appear within a few minutes, to a few hours, after the diver surfaces. The symptoms are usually alleviated by 100% oxygen, but this lasts only as long as the oxygen is being breathed. All symptoms, no matter how insignificant, can mushroom to more serious symptoms if not treated by recompression therapy. 3.8 Treatment for Decompression Sickness The ONLY treatment for Decompression Sickness (DCS) is recompression therapy in a recompression chamber breathing as high a concentration of oxygen as possible. The Coastguard should be the emergency service that co-ordinates the evacuation. Recompression reduces bubble size and may restore circulation to the affected areas of the body. Reduction in bubble size may also help bubbles to be passed to the lungs and expired. Higher ambient pressure in recompression may allow gas to be re-absorbed into the tissues then released in a controlled way. Breathing hyperbaric oxygen in the chamber or 100% O2 at the site helps by increasing oxygenation of hypoxic tissues. The level of nitrogen intake is also reduced and this helps to reduce the overall amount of nitrogen in the system. ENTONOX, carried by Paramedics, must not be administered to divers with suspected DCS. First Aid for DCS A rapid response to any suspected case of DCS greatly helps the effectiveness of the treatment: the first hour after surfacing is often referred to as the ‘Golden Hour’, as prompt treatment often aids faster recovery. If DCS is suspected, do not delay in asking for medical help; the Coastguard do not get concerned about callouts to cases that may be DCS but prove afterwards to be something else. Although oxygen administration should only be carried out by trained persons, a brief overview of the procedures for DCS first aid is useful. We would encourage all divers on this course to regularly update their First Aid, Oxygen Administration and Heart Start qualifications as a matter of course. The flowchart overleaf gives a distilled version of first aid for DCS. The NHS casualty checklist can provide valuable information on the casualty’s progressing condition.

29

NHS Casualty Checklist (www.sdm.scot.nhs.uk/decompression_illness/checklist.pdf)

Dive Information: Diver’s Name............................................Today’s Date.....................................

Sex (Circle) F M Age.............................

Gas Used................................................. Dive Description.................................................................. Time In......................................................Time Out...........................................

Depth...................................... Bottom Time.....................................

Ascent Stops........................................ Repetitive Dives....................................... When was their previous dive?

............................................................................................................................. Any problem with dive? .............................................................................................................................

Symptom Check List. Record responses:

Symptom Y/N Details (eg location of pain etc) Assess (include time)* Pain 1 2 3 4

Weakness Numbness etc

Breathing Difficulty

Normal Bladder Function Nausea or vomiting Dizziness Visual Upset Orientation/

Personality Change

* Assessment Key: �Improvement; �Worsening; ? No change

Casualty Checklist The NHS casualty checklist is a useful resource to take to a dive site, and can aid in the collection of valuable information on the casualty’s progress. It can be downloaded at: www.sdm.scot.nhs.uk/decompression_illness/checklist.pdf As well as basic information on diver, dive profile and history, it includes a progress checklist and neurological test.

30

Perform Neurological test if time allows. Record responses: Ask question: • Where does it hurt?

• When was it worst?

• When did symptoms occur? Orientation: • Does the diver know their name and age, day and date,

current location?

• Does the diver appear alert? Eyes: Check each eye separately by holding up fingers and asking diver

to count different numbers. Get the diver (from 0.5m) to follow one finger, first up and down then side to side. Is the movement smooth, and are the pupils the same size?

Face: Ask them to smile. Is muscle contortion the same on both sides?

Tongue: Ask them to stick out tongue. It should come straight out with no sideways deviation.

Muscle Strength:

Push on shoulders while they shrug. Is the pressure equal and strong? Ask them to raise each arm and push against your hands. Are both sides equal and strong?

Sensory: Close diver’s eyes and lightly touch points down each side of the body. Where do they NOT feel your touch?

Co-ordination Have them stand with their feet together and arms stretched out in front and eyes closed. Be prepared to catch them. Do they wobble or fall? Note if one arm drops Ask them to touch their nose and your finger (0.5m away) rapidly a few times

Feet: Take off socks and run a pointed instrument up the sole. If the toes curl down, this is normal. If nothing happens no conclusion can be drawn. If they curl up, this is a reliable sign of spinal involvement.

Further comments

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4 Oxygen, Carbon Monoxide and Carbon Dioxide Poisoning 4.1 Introduction Breathing air consists primarily of 21% oxygen and 79% of nitrogen. Oxygen is required to support respiration and hence life whilst nitrogen is inert and is not required for life. Lecture 2 has already outlined the problems of nitrogen narcosis; however, on deeper dives oxygen toxicity can also be an issue. In addition, other problems can be caused by carbon monoxide and dioxide poisoning. Fortunately the dangers can be minimised by proper training, careful maintenance of dive equipment and compressors, and the use of safe operating procedures. Avoiding deep, long and arduous dives can also help to minimise the risk to the diver. With the possible exception of carbon monoxide, the main dangers with these gases occur at depth (30m and beyond) and at higher than normal partial pressures. 4.2 Oxygen Toxicity Oxygen is essential if life is to be sustained. We live in an atmosphere that is made up of 21% oxygen (pp oxygen = 0.21 Bar); almost all of the rest is nitrogen. If pp of Oxygen falls below 0.15 Bar, hypoxia occurs and can damage or kill the body. Where no oxygen is present, anoxia will occur, causing death. In deep diving, the oxygen we need to support life can in fact become toxic to the body due to a pp of oxygen that is too great. This can occur at a pp oxygen of 1.6 bar or more. When diving on nitrox, the depth at which oxygen toxicity effects divers will be considerably shallower, based on the nitrox mix. When diving using a rebreather, oxygen toxicity may occur due to equipment malfunction. The two forms of toxicity are discussed in the following sections. Chronic Oxygen Toxicity Chronic oxygen toxicity is encountered if breathing with a gas mixture with a higher percentage of oxygen at surface pressure for a long time e.g. oxygen tent (max. = pp 1 bar O2 = 100% pure O2). Whilst this is not a concern for divers, knowledge of the symptoms is useful. Breathing oxygen at pp above 0.6 Bar for long periods of time produces irritation in the respiratory tract and lungs. The symptoms experienced are:

• coughing

• pain in the chest

• considerable discomfort - especially when deep breathing - and fatigue. The symptoms are similar to bronchitis or pneumonia, and the extent and rate of development depends on the pp of oxygen being breathed and the duration of the exposure.

Using pure (100%) oxygen, it takes 6 to 8 hours before symptoms start to be seen, and it may take up to 24 hours in some cases. The times required before experiencing chronic oxygen toxicity lie well outside the sport diving environment. It is really only a consideration for saturation divers and for people experiencing longer-term recompression therapies. In

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both of these situations there will be substantial logistical and medical support. In sports diving, the surface intervals effectively ‘reset’ the oxygen clock to zero. Acute Oxygen Toxicity (CNS) When oxygen is breathed at very high partial pressures the effects on the body are different and the onset of symptoms is very much faster compare to chronic oxygen toxicity. On very deep dives, or dives using nitrox, divers can achieve these very high partial pressures of oxygen quite easily. Acute oxygen toxicity can become a real danger for some divers who dive beyond 55m on air. The pp of oxygen regarded as the threshold for acute oxygen toxicity used by the Royal Navy is 1.6 bar, which equates to 67m, but they work with very fit, well-trained divers with lots of logistical and medical support. The ScotSAC recommendations are that a pp of oxygen of 1.4 Bar should not be exceed except in emergency situation. One reason for a safety margin is the variability in the reaction to high pp of oxygen. Different individuals respond differently, and an individual may experience different reactions to the same pp of oxygen on different dives and different days. High pp of oxygen of up to 3.0 bar can be tolerated during therapeutic recompression BUT this is in a dry chamber, at rest, with medical support, and the facility to revert to breathing air if problems occur. In the event of a malfunction or incorrect use of a rebreather, acute oxygen toxicity may occur. Symptoms of Acute Oxygen Toxicity If a diver is suffering from acute oxygen toxicity they will experience four distinct and different phases: 1. Pre-tonic phase 2. Tonic phase (Rigid) 3. Clonic phase (Convulsive) 4. Post convulsive phase (Relaxed) Unfortunately, the diver may not obviously exhibit any of the pre-tonic symptoms and may pass straight on into the next phase, or the first phase may be so brief that there is no time to react. If the pre-tonic symptoms are recognised early enough it may be possible to ascend out of the dangerous high pp oxygen depths. However, in some cases this has no effect and the condition continues to get worse. Pre-tonic phase During this phase the diver may experience some of the following symptoms.

• Apprehension

• Twitching of the facial muscles and lips

• Dizziness

• Nausea

• Unusual tiredness

• Disturbances in breathing

• Euphoria or depression

• Hearing disturbances

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• Tunnel vision and colour disturbances This phase may be very brief, allowing little time to react to the situation. The diver may appear to pass directly on to the second, tonic phase. Tonic Phase (Rigid) Once into this phase the diver will progress through this and the remaining two stages. There is no way to prevent it. From this point on the diver is helpless and will die, unless rescued.

• The diver loses consciousness and suffers a muscle spasm where all of the voluntary muscles go rigid. The muscle spasm will normally cause the diver to clench his teeth holding the regulator in place. There is a chance that the mouthpiece could be bitten through.

• The diver’s back arches and the rigidity lasts between 30 – 120 seconds. During this phase the diver will be holding his breath and not breathing. Attempted rescue during this phase may lead to pulmonary barotrauma.

Clonic Phase (Convulsive)

• As soon as the tonic (rigid) phase ends the diver suffers from violent convulsions. This can resemble a ‘grand mal’ epileptic fit. These convulsions are extremely powerful and violent. They can be strong enough to tear muscles or break bones in the casualty.

• The diver’s breathing restarts in this phase. If the regulator has been lost from the mouth the diver will drown.

• The violence of the convulsions make it very difficult to effect a rescue at this stage.

• The clonic (convulsive) stage can last for 2 - 3 minutes.

• There is little option in this stage but to allow the convulsions to come to an end before attempting a rescue.

• The convulsions may cause the regulator to be thrown from the casualty’s mouth; if this happens it is very likely that the diver may drown.

Post Convulsive Phase (Relaxed) Following the convulsions the diver collapses exhausted. They will become limp and, if the regulator is still in place, their breathing settles down. The casualty, however, does not regain consciousness. It is during this relaxed phase that rescue attempts are most likely to succeed. Rescue If the diver is not rescued to shallower depths, and ultimately the surface, they will continue to undergo cycles of clonic convulsions and post convulsive relaxation until death by oxygen poisoning or drowning occurs. Further cycles may continue during and after rescue so a diver should have regard for their own safety when attempting to rescue a casualty. Treatment The treatment for all acute oxygen toxicity symptoms is to remove the casualty from the O2 source to lower the inspired ppO2. The symptoms will dissipate with no lasting side effects, assuming they do not drown.

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Factors Affecting Oxygen Toxicity There is evidence that work rate affects the degree of risk; hard physical effort, high levels of carbon dioxide retention, stress and anxiety, feeling cold, fatigue are all contributing factors. More importantly, poor physical condition and illness are factors. Someone who is unfit produces 2 – 3 times more carbon dioxide than a fit person for any given work rate. Illnesses, including hangovers, may all increase the risk to the diver. The presence and extent of these factors may change during the course of a dive. A diver may be operating at depth without apparent problems. If the situation changes and the diver has to work harder there will be a rise in carbon dioxide production; this may also induce additional stress and fatigue due to a lack of fitness. Any or all of these factors could precipitate a CNS attack. 4.3 Carbon Dioxide Poisoning High levels of carbon dioxide are almost always due to contamination of the breathing gas, usually due to a poorly-sited, poorly-operated, or poorly-maintained compressor. A build up of carbon dioxide in the body is known as hypercapnia. ‘Skip breathing’ can also increase the levels of carbon dioxide in the body. In rebreather diving, carbon dioxide can build up as a result of scrubber exhaustion or bypass. Carbon dioxide build up also has an important influence on narcosis, oxygen toxicity, DCS, and hypothermia. As the level of carbon dioxide in the body increases, the diver may experience the following initial symptoms:

• apprehension and anxiety; this may not be readily noticed due to the general level of apprehension present in most deeper dives

• shortness of breath

• rapid shallow breathing / panting: this is not an efficient form of respiration and panting can make the problem of carbon dioxide build up worse.

• headaches: this is a very common and easily recognisable symptom.

• nausea

• dizziness As the carbon dioxide levels continue to rise:

• the pulse rate increases

• dilation of surface blood vessels causes a flushed feeling, esp. on the face.

• visual impairments

• muscle twitches

• convulsions

• unconsciousness

• death Very high levels of carbon dioxide are necessary to produce convulsions. 30-40% carbon dioxide will cause convulsions and unconsciousness almost at once, and death very quickly.

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4.4 Carbon Monoxide Poisoning Carbon monoxide is a colourless and odourless gas produced by inefficient combustion in fuel engines or through cigarette smoke. It is potentially the most dangerous contaminant of breathing gas as it is odourless and the onset of symptoms is rapid. A diver is likely to encounter carbon monoxide through contaminated air supplies. This is almost always due to poor compressor operation or maintenance. It is most likely to occur if the air intake is situated too near to the exhaust outlet, although a compressor operator smoking beside the air intake can cause problems. Dive compressors MUST be well sited and well maintained, and operated by competent personnel. If a diver smokes immediately before a dive they may descend with a higher than usual level of carbon monoxide in their lungs and may experience mild symptoms of carbon monoxide poisoning. Carbon monoxide combines with the haemoglobin in the red blood cells to form carboxyhaemoglobin. Carbon monoxide is almost 300 times more efficient at binding to haemoglobin than oxygen, preventing the oxygen being transported around the body and reaching the tissues of the body. Because carbon monoxide is a contaminant of the breathing gas, the diver will receive increasing pp of carbon monoxide as the depth increases. The increased partial pressure increases the rate of carbon monoxide absorption. There is some evidence that this faster absorption is partly countered by the higher pp of oxygen. For this reason some symptoms are sometimes only experienced as the diver ascends and the higher pp of oxygen reduces. There may be no physical signs of carbon monoxide in the breathing gas at surface pressure. The maximum carbon monoxide concentration in breathing air permitted is 5 parts per million. A contamination of 40 parts per million would have only a small effect at surface pressure and would be barely noticeable, but at 40m (at 5 bar) would be far more serious. The extent of the toxic effect will depend on the degree of contamination (the amount of carbon monoxide present) and the length of time the diver is exposed to it. Symptoms of Carbon Monoxide Poisoning The symptoms of carbon monoxide poisoning are similar to those of progressive hypoxia:

• Dizziness and headache

• General malaise and feeling unwell

• Slurred speech

• Mental confusion

• Lack of physical co-ordination

• Cherry red lips and cheeks

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• Collapse and coma

• Death Death will occur when about two thirds of the haemoglobin has combined with the carbon monoxide, or earlier if the diver’s loss of control causes an incident which leads to a fatal event such as drowning. Headaches after diving seem to be a very sensitive indicator of carbon monoxide poisoning. If all the divers on a dive are using air from the same compressor and several of them complain of headaches after a dive, the purity of the air from the compressor, and the location of the compressor should be checked. Treatment of Carbon Monoxide Poisoning Remove the diver from the contaminated air supply and allow to breathe pure air or 100% oxygen if available. In very mild cases that is all that is needed and the carbon monoxide will be eliminated in 6 - 8 hours. In most cases more active intervention is required. Oxygen should be given to speed up the recovery. The use of hyperbaric oxygen in a recompression chamber increases the efficiency of the treatment. The higher pp of oxygen helps to displace the carbon monoxide and increases the oxygen in solution in the blood plasma, helping to relieve any hypoxic tissues. This is the definitive treatment for severe carbon monoxide poisoning. Administer any first aid and EAR as required and seek medical help.

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5 Underwater navigation and search methods 5.1 Introduction This lecture covers the various methods used to aid underwater navigation, from recognition of key underwater features to detailed compass use. In addition, the different search methods which can be employed underwater are explained in more detail. 5.2 Underwater Navigation Underwater Navigation is the ability to follow a course during a dive from the entry point to the planned exit point, hopefully in a pre-determined time. Reasonably accurate navigation is not simply an exercise to be completed during training, but a means of diving with greater enjoyment or pleasure, and with greater safety. Navigation is primarily the responsibility of the Dive Leader. Although the Dive Leader runs the dive in the water his Buddy should also keep track of the position and direction in case they get separated. Different dives may place different navigational demands upon the diver. It may need no navigation when good boat cover and SMBs are used, although this should not really be an excuse for not knowing where you are. It may require navigation in a general direction:

• South to shore or shallow water.

• Swim west and the boat cover will follow you.

• Swim east towards the drop off.

Or it may require navigation to a precise point:

• To a predetermined, safe exit point. • To a shot line or decompression line.

• To a particularly interesting part of a wreck or reef. Perhaps the best aid to navigation is sensible and sound dive planning. This involves knowing about the dive site before jumping in: what is the bottom like, what is the depth profile? Plan the route before entry and ensure all members of the dive party know what is planned. Navigation is not just for the Dive Leader: the Buddy should also try to keep track of the direction and movement underwater. Having planned the dive, stick to it: “plan the dive and dive the plan”. 5.3 Aids to Navigation Navigation on land is often accomplished by using a map and reference to visual features on the landscape. The map gives you the ‘big picture’ and is often simply a case of walking to a distant landmark or way point, then locating the next landmark or way point and walking to it. Take away the map, or reduce the visibility with fog or darkness, and the navigation becomes much harder. A diver underwater does not have good maps and often has to contend with limited visibility. This can make the location of way points difficult. With only limited use of land based methods, divers have to make use of other cues to assist in navigation and position fixing underwater. In reality, the diver will not rely on only one method but will use a variety of different techniques to assist him to navigate underwater.

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Depth The depth of water can give an indication of the direction and position of the shore. Shallower water tends to be nearer the shore and deeper water further out. If a diver knows the site, depth can also give general indications of position underwater. However, depth profiles can vary considerably and are rarely steady. It is important that divers treat these cues with caution, especially if unsure of the bottom profile of a particular dive site.

05

10

15

20

Depth (m)

xEntry Point

“Enter from beach, descent to 15m and swim along contour with slope to your right” ����

05

10

15

20

Depth (m)

xEntry Point

“Enter from beach, descent to 15m and swim along contour with slope to your right”

05

10

15

20

Depth (m)

xEntry Point

“Enter from beach, descent to 15m and swim along contour with slope to your right”

05

10

15

20

Depth (m)

05

10

15

20

05

10

15

20

Depth (m)

xEntry Point

“Enter from beach, descent to 15m and swim along contour with slope to your right” ����

Light Using light can be a very imprecise method of navigation. The amount of light in the water may give clues to both up and down (lighter above and darker below), and perhaps water depth (shallower water near shore is often lighter). In good conditions the direction of the light and darker areas caused by shadows of reefs or wrecks can be useful for navigation.

Current Tides or currents often flow in predictable directions and can aid navigation. A strong current can destroy any pretence of navigation as it may only be a choice of going with it, or aborting the dive. Currents are most predictable in areas where the coastline and sea bottom are relatively featureless. Unfortunately, these are not always the best places to dive. Headlands, reefs and drop offs are more interesting but can divert currents and eddies and the flow of water can become quite confused.

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Natural features and debris These can be used very effectively, particularly in sites where the topography of the bottom is not too complex; this is the most common way divers navigate. In its simplest form it can be “Swim with the rock face on the right hand side”, or “Swim out with the rock face on the right and come back with it on the left”. If the dive site is known and dived frequently, the diver may become familiar with the layout and recognise particular features, allowing them to keep track of position. It may be that all the reefs run at right angles to the shore and following a reef west will lead back to shore. A reef may end at 20m, or in a sandy bottom; if a diver finds themselves at at 25m or on a sandy plain they have gone too far and will need to track back to the reef. In areas where the bottom is reasonably uniform and sandy, the sand may form ripples facing across the current. This can be used to help direction finding but as the marks in the sand are fluid they are can be unreliable.

During a dive, features and litter on the bottom that are easily recognised can help to pinpoint position. These can prove useful when swimming reciprocal courses on an individual dive.

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5.4 Use of a Compass A magnetic compass can be a valuable tool to help a diver with navigation both above and below water. In order to be used underwater a diver’s compass must be waterproof and able to withstand the pressure to which the diver will descend. It must swing easily and be able to rotate freely without having to be held absolutely horizontal (this is not always easy underwater). A sealed, oil filled compass will perform well. It should also be of a size that is easily read and have a bezel graduated from 0o - 360o , a ‘Direction of Travel’ line and possibly a moveable indicator to mark the bearing. There are two types of compass used underwater: fixed and moveable bezel compasses. The bezel in a fixed bezel compass does not rotate. The 0o - 360o scale is marked in reverse (anticlockwise) around the bezel. There is usually a marker that can be rotated to line up with any point on the bezel. The bezel in a moveable bezel compass can be rotated. The 0o - 360o scale is marked (clockwise) around the bezel. There is usually a marker on the bezel that can be rotated to line up with any point on the north end of the compass needle. A compass will always indicate the position of magnetic north. However, the diver should be aware that metal objects and anomalies may cause local variations. The compass should be held directly in front of the mid-line of the body as the diver will tend to swim along the line of the mid-line of the body. If the ‘Direction of Travel’ line and the mid-line of the body point in different directions the diver will tend to follow the line of the mid-line of the body, NOT the ‘Direction of Travel’ (the bearing). The main reason for this error happening is holding the compass off centre. For the best results you should reach right round and hold the compass in front of your face. A compass in a console or on a lanyard may make this easier to achieve.

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Using a compass underwater Straight line navigation is the most common way in which a compass is used underwater. The diver uses it to help maintain a straight line course. The physical difficulties of navigation underwater (poor visibility, current etc.) and the fact that the degree scale is usually marked in 5o increments, at best, makes really accurate navigation very difficult. The diver is unlikely to be able to swim a complex compass course, or a course over a long distance and end up exactly at the planned destination. To swim a straight line course:

• Set the compass to a landmark or desired bearing.

• Hold the compass directly in front of the mid-line of the body.

• Ensure the compass is level and can swing freely.

• Ensure that the north end of the compass needle and the marker on the rotating bezel are lined up.

• Look well ahead along the ‘direction of travel’ line and locate a landmark or object on the bearing to follow. In very poor visibility the diver can only watch the compass alignment.

• Swim towards it, keeping an eye on the compass alignment. On reaching the landmark look further ahead along the ‘Direction of Travel’ line and locate another landmark or object on the bearing to help keep on track.

A Reciprocal Course (Out and Back) - Swim the outward course using straight line navigation techniques. On reaching the end point, either add 180o to the original bearing (giving a reciprocal bearing) or realign the moveable marker to line up with the south end of the compass needle, taking care not to move the compass body when doing this. Rotate the compass to realign the north end of the compass needle with the moveable marker to set the compass for the reciprocal bearing.

0m

5m

10m

15m

20m

0m

5m

10m

15m

20m

Out: 120o

Back:3000

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0m

5m

10m

15m

20m

0m

5m

10m

15m

20m

Out: 120o

Back:3000

COMPLEX COURSES –If the dive site is known well, it is possible to plot complex compass courses involving several legs swum along different bearings, tracing a route to and from an objective. While this is technically no more difficult than navigating reciprocal bearings, it does involve more calculations and, therefore, greater chance of error. Remember that mental arithmetic is one of the first skills to be affected by nitrogen narcosis. This chance of error can be reduced if the course is plotted first on land and the bearings recorded on a slate which is carried on the dive. In general, if the diver turns to the right, the angle through which the diver has to turn is added to the previous bearing.

If the diver turns to the left, the angle through which the diver has to turn is subtracted from the previous bearing.

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Complex courses are a mixture of both methods:

Estimating distance underwater: It can be extremely difficult to accurately judge the distance travelled while swimming underwater. The variable nature of the situation, particularly in relation to currents and individual diver fitness, makes it hard to make easy-to-use rules. A diver can rarely see far enough to see the intended destination and for much of the time may be swimming on a bearing. While the direction of swim can be closely monitored, distance is harder to judge. Different divers swim at different speeds and it is important to have a rough estimate of average speed. This can be done by swimming known distances and noting:

• The time taken to cover the distance.

• The number of fin strokes taken to cover the distance.

• The number of breaths taken to cover the distance. This will only work if the diver swims at a uniform and reasonably constant pace on all dives. It is worth establishing a routine and a uniform “cruising” pace. Currents can destroy this method of judging distance. It may be impossible to make headway swimming against a current. Swimming with a current may increase the speed of a diver four-fold. In these conditions the diver must estimate distance based on experience and knowledge of a variety of situations.

Complex Profile – combination of left and right turns

1

2 3

45

250290-40=40 left5

290135+155=155 right4

1350+135=135 right3

045-45=45 left2

451

Bearing (o)WorkingsTurn (o)Leg

250290-40=40 left5

290135+155=155 right4

1350+135=135 right3

045-45=45 left2

451

Bearing (o)WorkingsTurn (o)Leg

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5.5 Underwater Search Methods If something is lost underwater it can be extremely difficult to locate. From the surface there may be very little in the way of clues to help locate it. Small objects can be very difficult to find, but even quite large targets can prove frustratingly elusive. The difficulty in locating an object underwater is compounded by the same problems that affect accurate navigation underwater. Poor visibility, water movement and currents, and the difficulty in keeping track of where you are and how far you have travelled all make organised search patterns extremely tricky to carry out efficiently. Factors to bear in mint:

• Underwater searches need a methodical approach.

• Know what is being searched for, especially how big it is.

• Know a rough (or exact) location in which to search.

• Know the type of seabed and general conditions (visibility., current etc.).

• Know how many divers are available to support the search.

• Have a plan of action.

• Effectively cover the whole of the area to be searched.

• Conduct the search safely. Circular Sweep Search Used to search a known location efficiently and can be used to locate quite small objects:

• An anchor line or shot line is dropped at the location to be searched.

• Two, or more, divers descend to the bottom of the line.

• One diver stays at the bottom of the shot line and supports the search line clear of obstructions on the bottom.

• The other diver takes the reel of the search line out to the limit of visibility until the diver can just see the next diver clearly. If there are more than two divers they space out along the line, depending on the visibility.

• The lead diver, the end one with the reel, takes a bearing using a compass. It is easiest to take one of the cardinal points (N, S, E, W).

• On a predetermined signal, the lead diver swims in a circle a couple of metres off the bottom, visually searching for the target object.

• If the target object is not located by the time the lead diver has completed the circle and is back to the original bearing, the line can be extended and the procedure repeated.

• If the target object is found, the dive party signal success using tugs on the rope.

• The target object is then recovered or marked with an SMB.

• The lead diver carefully rewinds the search line onto the reel and the search party return to the shot line

5m 10m 15mStart Point

Object

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Spiral Search This is a search pattern suitable for a dive pair covering a small area. It can be used to locate quite small objects but is difficult to navigate accurately and it may be hard to ensure that all the search area has been effectively covered.

• The diver starts at a point where the target object is though to be.

• The first line of the search follows an obvious bearing; cardinal points are best.

• After a short distance determined by visibility (e.g. 5m) the diver turns 90o and continues the search pattern. The second leg of the search is equal in length to the first (5m).

• The diver again turns 90o and continues the search pattern. The third leg of the search is equal double the length to the first two (10m).

• This pattern is repeated to form a spiral with legs: o 1 and 2 being 5m o 3 and 4 being 10m (2x 5m) o 5 and 6 being 15m (3x 5m) o 7 and 8 being 20m (4x 5m)

The difficult part of this search is accurate distance judgement underwater and the ability to swim an accurate bearing while concentrating on another task - the search.

Jackstay Search Used to search a known location along a known line. This search pattern can cover a larger area than a circular sweep search. Adjacent parallel lines can be searched to cover a square section area. This search pattern can be used to locate quite small objects:

• A line is laid on the bottom across the area to be searched. Often the ends are marked with buoy lines.

• The searching divers swim up one side of the line, scanning the bottom on that side for the target object.

Start Point

Object

1

2

3

4

5

6

7

8

9

1 5m E

2 5m N

3 10m W

4 10m S

5 15m E

6 15m N

7 20m W

8 20m S

9 25m E

Start Point

Object

1

2

3

4

5

6

7

8

9

1 5m E

2 5m N

3 10m W

4 10m S

5 15m E

6 15m N

7 20m W

8 20m S

9 25m E

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• At the end of the line the diver swims back down the opposite side of the line again scanning the bottom on that side.

• If the target object is not located on the first pass the search line is moved as illustrated below.

• The distance the line is moved depends on the visibility and type of seabed, but the new search area should overlap the previous sweep to ensure total coverage.

• The diver searches up and down the line as before, scanning for the target object.

• This process can be repeated as necessary. If the target object is located it can be recovered or marked as required.

1 2 3 4

Swim Line Search If several divers are available, a Jackstay Search can be extended to cover a larger area by using a Swim Line Search Pattern.

• A line is laid on the bottom across the area to be searched similar to a Jackstay Search. Often the ends are marked with buoy lines.

• A second parallel search line can be laid, the distance apart being governed by the visibility, the type of seabed and the number of divers available.

• A line is stretched between the two search lines and the searching divers space themselves out along the line, the distance apart being inside the limit of easy visibility.

• On a predetermined signal from the lead diver, the search team swims down the channel between the two search lines, scanning the bottom for the target object.

• At the end of the line the search team can either retrace their path searching in the opposite direction, or move one line beyond the other and re-lay it on the same bearing and parallel to it.

• The search pattern is repeated with the end diver covering the last channel searched in the previous search to allow an overlap.

• This process can be repeated as often as is required.

• If the target object is found, the dive party signal success using tugs on the rope.

• The target object is then recovered or marked with an SMB.

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2

1

Snag line search This is set up in a similar fashion to a swim line search with two parallel search lines laid on the bottom. Two divers swim along these lines, slightly off the bottom, towing a rope between them. The plan is to snag the line on any large object on the bottom which will then be investigated. This type of search pattern needs a relatively flat and unobstructed seabed and a reasonably large target object. Large areas can be covered by a pair of divers and the search can proceed in poor visibility if necessary.

• A line is laid on the bottom across the area to be searched similar to a Jackstay Search. Often the ends are marked with buoy lines.

• A second parallel search line can be laid, the distance apart being governed by the visibility, the type of seabed and the number of divers available.

• A line is stretched between the two search lines and the searching divers who follow the search lines.

• On a predetermined signal from the lead diver the two divers swim down the channel between the two search lines, towing the line between them, hoping to snag the target object.

• At the end of the line they move one line beyond the other and re-lay it on the same bearing and parallel to it.

• The search pattern is repeated with the end diver covering part of the last channel searched in the previous search to allow an overlap.

• This process can be repeated as often as is required.

• If the target object is found it can be recovered or marked with an SMB.

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6 Basic Seamanship 6.1 Introduction This lecture provides basic information about navigation, seamanship and safety at sea for divers. It is not a substitute for appropriate boat handling and advanced navigation training. 6.1 Weather Weather is a constantly changing and sometimes unpredictable force of nature. At sea, the effects of changing weather can be disastrous if contingencies have not been made. Weather forecasts are vital to safe dive planning as the weather can have a significant effect on the sea state. Whilst rain or fog may have little effect on the dive underwater, it can significantly reduce above-water visibility, making it difficult to locate divers in the water and navigate safely to shore. The Wind The direction and strength of wind can significantly increase the size of waves, and render some dive sites inaccessible. In addition, a strong headwind can increase the duration of transit to a dive site and increase the fuel required. Onshore winds blow from the sea towards the land. This can cause swell in shallow water, render shore diving inaccessible and can significantly reduce visibility. Exposed harbours, pontoons or slipways can be more difficult to access during onshore winds. Offshore winds blow from the land to the sea and, in general, calm inshore waters. However, they can be dangerous to any diver on the surface of the water as the diver can drift a significant distance from their shore / exit point. The Beaufort scale is used to estimate wind speed. A copy can be found in the back of any ScotSAC log book, and is reproduced on the following page. The wind force is divided into 13 units ranging from 0 (calm) to 12 (hurricane). Above Force 4, diving comfort and safety on exposed sites will be affected. Pressure fronts and maps The British Isles lie between the cold air masses emanating from the polar region and the warm air masses from the Tropics. Pressure maps show contours of atmospheric pressure (isobars), which indicate the effect of mixing of these bodies of air. Where cold air advances underneath warmer air, a cold front develops. Pressure begins to fall as the front approaches and rain normally starts as it arrives. Once the front has passed the pressure will begin to rise and wind may change. Showers may also form.

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The Beaufort Scale Equiv. speed 10m above ground Force Description Miles/hr Knots

Land Criteria Sea Criteria c. height of waves (m)

0 Calm 0-1 0-1 Calm; smoke rises vertically Sea like a mirror -

1 Light air 1-3 1-3 Direction of wind shown by smoke drift, but not by wind vanes

Ripple with the appearance of scales are formed, but without foam crests

0.1

2 Light Breeze

4-7 4-6 Wind felt on face; leaves rustle; ordinary vanes moved by wind.

Small wavelets, still short but more pronounced, crests have a glassy appearance. Perhaps scattered white horses

0.2

3 Gentle Breeze

8-12 7-10 Leaves and small twigs in constant motion; wind extends flag.

Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses.

0.6

4 Moderate Breeze

13-18 11-16 Raises dust and loose paper; branches are moved.

Small waves, becoming longer, fairly frequent white horses 1.0

5 Fresh Breeze

19-24 17-21 Small trees in leaf begin to sway; crested wavelets form on inland waters.

Moderate waves, taking a more pronounced long form; many white horses are formed. Chance of some spray.

2.0

6 Strong Breeze

25-31 22-27 Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.

Large waves begin to form; the white foam crests are more extensive everywhere. Probably some spray.

3.0

7 Near Gale 32-38 28-33 Whole trees in motion; inconvenience felt when walking against the wind.

Sea heaps up and white foam from breaking waves begin to be blown in streaks along the direction of the wind.

4.0

8 Gale 39-46 34-40 Breaks twigs off trees; generally impedes progress.

Moderately high waves of greater length; edges of crest begin to break into spindrift. The foam is blown in well-marked streaks along the direction of the wind.

5.5

9 Severe Gale

47-54 41-47 Slight structural damage occurs (chimney-pots and slates).

High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility.

7.0

10 Storm 55-63 48-55 Seldom experienced inland; trees uprooted; considerable structural damage occurs.

Very high waves with long over-crests. The resulting foam, in great patches, is blown in dense white streaks along the direction of the wind. On the whole the surface of the sea takes on a white appearance. The 'tumbling' of the sea becomes heavy and shock-like. Visibility affected.

9.0

11 Violent Storm

64-72 56-63 Very rarely experienced; accompanied by wide-spread damage

Exceptionally high waves (small and medium-size ships might be for a time lost to view behind the waves). The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility affected.

11.5

12 Hurricane 73-83 64-71 -- The air is filled with foam and spray. Sea completely white with driving spray; visibility very seriously affected.

14+

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Where warm air advances over colder air, a warm front develops. Clouds thicken as the front approaches and pressure falls. Rain will then fall, and will usually be heaviest on the front. Once the front has passed, there is generally a rise in both temperature and humidity and change in wind.

There are a number of sources for UK inshore marine forecasts, including BBC Radio 4, local radio stations, TV and websites. 6.2 Navigation - Basic Chartwork There are a number of published charts which cover the coastline of Britain. They are available in a variety of different scales to suit different users. Charts use symbols to provide information about the nature and position of features such as sea bed information, seamarks and landmarks, depth information, contours, and hazards. The position and characteristics of buoys, lights, lighthouses, coastal and land features and structures are also shown. Modern metric charts illustrate depth by colour coding and individual depth soundings. Positions of places shown on a chart can be measured from the longitude and latitude scales on the borders of the chart. One minute of longitude (1/60th of a degree) is equal to one nautical mile.

Equator

N

S

EW

Latitude

Longitude

Equator

N

S

EW

Latitude

Longitude

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The direction of true north is identified on a chart in the form of a compass rose. The magnetic north Pole is different from True north, and varies yearly. A chart compass rose may show a magnetic compass rose inside the true one, but it will only be valid for the year of publication. It is important to know the current variation for the relevant year. The Admiralty publication Chart 5011 gives information on all abbreviations and symbols found on Admiralty charts, and is a useful tool for the interpretation of charts.

© British Crown Copyright and/or database rights. Reproduced by permission of the controller of Her Majesty’s Stationery Office and the UK Hydrographic Office (www.ukho.gov.uk) NOT TO BE USED FOR NAVIGATION

© British Crown Copyright and/or database rights. Reproduced by permission of the controller of Her Majesty’s Stationery Office and the UK Hydrographic Office (www.ukho.gov.uk) NOT TO BE USED FOR NAVIGATION

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6.3 Tides Tides are caused by the gravitational pull of the sun and moon on the earth’s water. A tidal cycle lasts 24hrs 52 minutes, during which time two high and low tides will be experienced.

Spring and Neap Tides The position of the sun and moon relative to the earth influences the difference in height between high and low tide. When the moon is full or new, the sun and moon are in alignment and the gravitational force exerted on the earth’s water is greater, producing Spring tides, where the difference in height between high and low water is bigger. At half moon, the gravitation force of the sun pulls in a different direction to the moon, producing neap tides where the difference between high and low water is less. This cycle happens every 28 days as the moon orbits the earth.

High tide 06:00

You are here

tidal bulge

Low tide 00:39

High tide 18:26

Low tide 12:13

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Spring

tide

Spring

tide Neap

tide

Neap

tideSpring

tide

Spring

tide Neap

tide

Neap

tide

High Tide

Low Tide

BiggerRange

High Tide

Low Tide

BiggerRange

High Tide

Low Tide

SmallerRange

High Tide

Low Tide

SmallerRange

Spring Neap

Chart Datum As the actual depth of any body of water will vary with time, charts display depth relative to a chart datum, which is a point below the lowest low water point. At high and low tide, water is said to be ‘Slack’ – with little flow of water. As the tide turns from low to high, it is said to flow, and ebb on the return to low.

MHWS

MLWS MLWN

MHWN

neaprange

springrange

Chart Datum (CD) charted depth (below CD)

depth of

water

height

of tide

Height above MHWS

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(MHWS / MHLS – Mean High/Low Water Spring; MHWN/MLWN – Mean High/Low Water Neap) Rule of twelfths The ‘rule of twelfths’ illustrates the flow of water between tides and can be used to estimate depth. It assumes that the rate of flow of a tide increases to a maximum halfway between high and low tide, following a similar path on the ebb tide. In the first hour after LW, the water level will rise by one twelfth of the range, in the second hour two twelfths, and so on according to the sequence - 1:2:3:3:2:1. The rule of twelfths is only an approximation. Weather conditions and local topography and currents can significantly affect the flow of water.

Tidal Information Tidal information can be obtained from a variety of tide tables and online sources. These give the times of high water at standard ports with corrections for other ports. They also give the height of water at high water, which can be used to calculate the height for different stages of the tide. It is important to note that the height of tide can be influenced by strong winds, and barometric pressure. Software is now available giving tidal information in electronic format.

HeightOf tide

Charted

Depth

Chart

Datum

Depth of

water

LW

HW

Range

LW +1 +2 +3 +4 +5 HW+1 +2 +3 +4 +5 LW

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www.easytide.co.uk Worked Example: You plan to dive at 12:00 at the spot located on the chart. What depth should you expect to encounter the sea bed?

20

30

22

21

25

25

27

33

18

1511

11

20

30

22

21

25

25

27

33

18

1511

11

1000 LW 3.0

1607 HW 9.0

Chart Datum: 25m 10:00 LW : 3m above CD = 28m 16:07 HW : 9m above CD = 34m Difference between HW and LW : 9-3 = 6m

Dive time 1200 – 2hrs after LW: (12

1 +12

2 ) of 6m

123 of 6m = 1.5m

Height of tide: LW+1.5m = 3 + 1.5 = 4.5m Depth of water: CD+4.5m = 25 + 4.5 =29.5m Tidal Flow Tides not only rise and fall, but in doing so create horizontal movements in the sea. The rising tide generally moves clockwise around the UK and vice versa on the ebb tide The momentum of

25m25m

LW 28mLW 28m

HW 34mHW 34m

29.5m29.5m

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© British Crown Copyright and/or database rights. Reproduced by permission of the controller of Her Majesty’s Stationery Office and the UK Hydrographic Office (www.ukho.gov.uk). NOT TO BE USED FOR NAVIGATION

the water and local topographic features cause variation in the timing, speed and direction of water movement. Admiralty charts use a system of diamonds to give information on the direction and speed of tidal currents relative to HW. This information is sometimes essential when planning a dive on a site subject to strong currents. . 6.4 Buoyage and Lights Buoys are fixed points and are useful for position finding in a small boat. They also give important information about the movement of vessels and underwater features. Lateral Marks Main channels into ports will be marked by red can buoys to port and green conical buoys to starboard as a vessel enters a harbour. The situation will be reversed on departure. Lights will be red and green respectively.

Cardinal Marks Cardinal marks are pillar-shaped and are aligned in a north, South, East and Westerly direction around an area of danger. There may or may not be more than one buoy marking the danger area (which may be the potential dive site). These buoys are coloured yellow and black and exhibit white lights in known combinations of (very) quick flashing and long flashing

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Danger

Clear to

WEST

Clear to SOUTH

Clear to NORTH

Clear to East

Danger

Clear to

WEST

Clear to SOUTH

Clear to NORTH

Clear to East

light combinations, altering depending in which quadrant the buoy lies. Each has a different ‘top mark’, depending on its alignment. Top marks are formed by two black conical cones: In the northern quadrant the points face north In the Southern quadrant the points face south In the Western quadrant the points face inwards In the Eastern quadrant the points face outwards Other Marks Isolated danger marks are red and black pillar-shaped buoys. Safe water marks are coloured red and white and either spherical or pillar shaped. Special marks are yellow and may be any shape.

Danger

Clear to

WEST

Clear to SOUTH

Clear to NORTH

Clear to

East

Danger

Clear to

WEST

Clear to SOUTH

Clear to NORTH

Clear to

East

+ +

Safe water mark

Isolated danger mark

Direction of

buoyage

Cardinal marker

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6.5 Navigation General The first requirement of a navigator is usually to get from A to B safely, without getting lost, in as short a time as possible. If they can see B when they set out, there may be little problem. However, if B is out of sight due to distance or poor visibility, they will need to know a course to steer. In order to navigate successfully a boat handler needs to:

• Find out where they are

• Find out where they want to sail to

• Find the best route to their destination

• Check that they are following their route

• Work out appropriate corrections if they have strayed from their course

The best route may not be the straightest. They must avoid areas which may be too shallow for the draught of their boat at the stage of tide they are making the trip, but will want to take the safest practical course. This may not be the shortest on the chart, as weather conditions may slow progress. A choice of two or more launching sites navigation methods will allow a decision on the shortest distance to be made. The answer may not be the nearest launching point. At some states of tide the current will flow against the direction of travel on the way out and again on the way back a few hours later when using one launch site, whereas one placed differently may give the aid of currents both way. On other days the different times and height of the tides might alter the timing and extent of the currents in such a way that the choice of launching sites may change. Simple Navigation Simple navigation requires four abilities:

Masthead Light (power only)

Portsidelight

Starboardsidelight

Stern LightDirection of buoyage

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• The ability to plan your course by marking on a chart from your starting point to your goal and read off the bearing of this course (i.e. the direction in relation to True (T) or Magnetic (M) north)

• The ability to use a compass on board the boat so that this course is steered

• The ability to have worked out a set of bearings from the chart that will enable the intended dive spot to be identified

• The ability to recognise when the boat has reached the point indicated by the bearings

The course to steer is obtained from a chart of the area. A parallel rule is laid along the course to be taken, and the course drawn on the chart. The rule is kept parallel and run on its rollers to the centre of the chart’s compass rose. The true course is then read off. In order to convert the reading to magnetic, the variation is added or subtracted. Transit Bearing For straight line courses, it is often useful to use a Transit bearing. A useful position line can be taken from two shore objects in transit. When on course, the two objects will be aligned. On drifting off course, the objects will become mis-aligned. It is important to remember that transit bearings give a direction but not distance.

Position fixing Position fixing to check that the desired destination has been reached can be can either by transit or compass bearings, or by a combination of both. The ‘three point fix’ is often used to estimate position. Bearings are taken on three or more objects on the shore which are also marked on the chart. The estimated position lies where the three position lines cross. In practice, the lines will rarely ever cross at the same point. The resulting triangle is known as a ‘cocked hat’. It should always be assumed that the boats position is the point in the triangle nearest to danger. GPS and echo sounder can be used to aid position fixing.

On course: mast and chimney aligned Off course: out of alignment

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Lighthouse

Cairn

Mast

Chimney

Lighthouse

Cairn

Mast

Chimney

6.6 Boats Boats allow divers to explore a much wider area, and access dive sites which are otherwise inaccessible from shore. Dive boats come in a variety of shapes and sizes ranging from dive kayaks, inflatables, rigid inflatable hulls (RIBs) and hard boats. Boat Layout Boats may be single or multi-hull with varying means of power (e.g. engine, paddle, oars). Deck and storage space is a must for divers, meaning that not all pleasure boats are suitable for diving. All boats have common terminology used to describe different parts of the boat including:

• Bow – the front of the boat in the direction of travel, usually pointed to cut through water.

• Stern – the rear of the boat in the direction of travel, and normally flat or slightly rounded.

• Transom - the surface that forms the stern of the boat, on which an outboard engine or other equipment may be mounted.

• Hull – the body or frame of the vessel

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Types of Boat The suitability of a boat as a diving platform will depend on its carrying capacity, stability and ease of re-entry.

• Inflatable – Small inflatable boats are useful for transferring from shore to larger boats. Larger, high capacity boats can carry a group of divers, but their handling characteristics in rough weather mean they are rarely seen as club boats.

• Rigid Hull Inflatable Boat (RIB) – popular as dive vessels due to their stability, speed and convenience. RIBs vary in size and are normally transported on a trailer and launched from a slipway. Due to its low freeboard, entry and exit to and from the water normally requires no additional ladder.

• Cathedral Hull – these provide greater space than any craft size for size and are extremely stable. Their main disadvantages are their hard sides and tendency to hammer at speed.

• Day Boat and liveaboards – chartering larger boats is often a good option for longer trips. The size and configuration vary greatly. Some now include hydraulic lifts to aid

Port

Starboard

Stern Bow

Cockpit Transom

Painter

Trim Tab

Outboard

Engine

Propeller

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divers returning to boat. Many dive day boats and liveaboards in the UK are converted Motor Fishing Vessels, providing a stable platform for diving.

Engines and Drives The type of engine fitted to a boat will depend on the size and purpose of the boat. There are three primary types of engine suitable for different vessels.

• Outboard: Outboard engines are often used to power small boats, and are attached to the transom. Fuel is supplied either from deck-based fuel tanks or tanks within the hull. Steering may controlled by a stern tiller, or central console with steering wheel. Outboard engines come with a choice of shaft length to adapt to the position of the transom on the boat. They can be tilted for beaching and the engine acts as a rudder.

• Inboard: The inboard motor is permanently installed, with the shaft exposed below the hull. The engine drives the propeller via the shaft. Fuel tanks are stored within the hull. Inboards may be fitted to larger RIBs or any day boat.

• Outdrive engines combine the characteristics of both inboards and outboards and are usually reserved for high powered units. The main engine is located within the hull, whilst the powerhead is located externally on the stern.

6.7 Rule of the Road The International Regulations on the Prevention of Collisions at Sea (IRPCS) gives internationally recognised rules for manoeuvring craft at sea. These are usefully summarised in the ‘Safety at Sea’ Lifeboat and RYA publications, available to download from www.lifeboats.org.uk. Some of the general principles are summarised below. Vessels under power:

• Give way to sail

• Approaching head on, give way to starboard (pass port to port)

• Crossing – vessel with other vessel on starboard side gives way

• Watch wash when passing close to other vessel

Cathedral Hull Dayboats Liveaboards

64

The following general rules aid in the prevention of accidents or injury:

• The skipper or coxswain of the boat should maintain a good lookout at all times, watching out for other vessels, points of danger or other navigation hazards. Others onboard should also keep a watchful eye.

• When overtaking, boats must keep clear of other vessels, allowing space. It is possible the vessel being overtaken is not aware of other vessels and may change course.

• If the bearing of an approaching vessel is constant, there may be a risk of collision.

• Keep to the right in narrow channels and harbour entrances

Approaching head on Crossing

A B

A BA B

Overtaken: maintain course and speed

Overtaking: make sure the other boat knows you are there

Overtaken: maintain course and speed

Overtaking: make sure the other boat knows you are there

65

At the dive site When divers are in the water, an ‘A Flag’ should always be flown. An A flag is an international symbol to other sea users, notifying them of your limitation of movement and advising them to keep well clear. Dive boats should be positioned to enable warning of other vessels, keeping them well clear of the area being dived. In some cases, such as drift diving, the use of a secondary boat will provide additional safety. The use of surface marker buoys by divers assist in marking their position. Safety at sea – general boat safety It is essential to choose an appropriate boat for the level of diving planned. A small inflatable may be suitable for a limited group of divers travelling to a local, sheltered dive site, but overloaded, and in rough water, it could easily become unstable. A competent boat handler should always be present when divers are underwater. Regular boat maintenance checks are essential and should be carried out by a competent person. Appropriate boat handling skills are required by any group taking to the sea in a boat. Boat handlers should also be familiar with methods of approaching and retrieving divers from the water. A boat should be properly equipped with standard safety equipment, including where relevant:

• Life jackets

• VHF radio / GMDSS

• EPIRB

• Flares

• First Aid kit

• Throwing line

• Fire extinguisher

• Paddles

• GPS / Echo sounder 6.8 Personal safety To ensure personal safety at sea, it is essential that all members of your dive group are appropriately clothed to avoid hypothermia or heat exhaustion. Life jackets should be worn where appropriate, and all drysuits should be zipped shut before departure. All should be familiar with the procedures for Man Overboard. “Man Overboard” Where possible, the casualty should shout on the way overboard to alert other members of the group. The casualty should try to remain in their original position to

www.lifeboats.org.uk

66

enable ease of location. The crew should shout “Man Overboard” and the boat handler should direct the crew to point continuously at the casualty. The boat should turn to approach the casualty from downwind; the final approach should be dead slow with engine engaged in neutral when coming alongside the casualty. If unable to locate the casualty within a short time, a MAYDAY should be relayed to the Coastguard. 6.9 Anchoring Anchors are used for fixing the position of a boat on the seabed, perhaps at a dive site, or during periods of non-diving (e.g. surface intervals or overnight). Anchors should to be attached to the vessel at all times and ready for use in the case of an emergency such as loss of engine power. Anchors are generally attached using a length of chain and anchor warp lines. The need may arise to ditch the anchor for retrieval later in which case a buoy is required.

Anchors usually consist of a central bar called the shank and an armature with a form of flat surface to grip the seabed. Some examples of anchor types include:

• Grapnel – simple, lightweight anchors which hook the bottom or other structures. Grapnels are often more difficult to retrieve, but can provide a more secure anchorage.

• Bruce/Plough – named due to the resemblance of an agricultural plough, and based on copies of the original ‘coastal quick release’ design: these anchors are general good in all bottoms but not exceptional in any.

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6.10 Basic Rope Work There are over four thousand recognised knots which can be used in varying situations. Divers may use ropes to attach anchors, secure a boat to a pontoon, trailer, decompression rigs, and more. Two commonly used and extremely useful knots are illustrated below: Bowline

A bowline is used to form a fixed loop at the end of a line. The loop will not tighten and can be useful, for example, for the end of a throw line or to fasten a mooring line to a post. It cannot be undone whilst under load so is unsuitable for situations requiring release under load.

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Anchor Bend An Anchor Bend is used to attach rope to a ring or fixed point.

Figure of eight This knot is a general purpose ‘stopping’ knot and provides a method of stopping ropes from running out of retaining devices. Round turn and two half hitches 6.11 Summary This lecture gives a basic introduction to use of boats, equipment and safety on the sea. It is intended to give background information for divers, and is not a substitute for appropriate boat handling training through appropriate training agencies.

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7. Expedition Organisation

7.1 Introduction This lecture provides a range of information on planning diving expeditions safely and effectively.

7.2 Expedition Organisation Depending on the nature of a Branch, members may have experienced a variety of dive trips, some of which will be considered expeditions, whilst others are routine training dives. The longer the trip and the further away, perhaps the more complicated the planning becomes as it requires consideration of accommodation and transport. Many dive clubs also charter live aboard dive boats, where many aspects of the organisation are taken care of by the Skipper, but care should be taken not to absolve responsibility, and to agree who is responsible for what.

Why have expeditions? There are a great number of reasons for taking part in expeditions, including the chance to:

• Carry out a greater number of dives in a short period of time

• Dive with a greater number of Buddies, building experience

• Dive in a greater variety of locations, building experience

• Get greater experience of dive planning and organisation

• Conduct training dives efficiently and effectively, with more Instructors present

• Dive with greater support and safety

• Dive with greater enjoyment

Divers develop experience through diving in a number of locations, with a number of buddies, and in a number of different conditions and situations. Expeditions take the diver away from their usual local training site and allow them to continue to develop their experience.

7.3 Expedition Organiser Having decided to organise an expedition it is then necessary to appoint someone as the Expedition Organiser. The Expedition Organiser does not have to do everything, but they must ensure that everything that needs to be done, gets done.

Delegation is a very useful skill for an Expedition Organiser. If people have particular skills then make use of them. If assistance is needed, ask for help.

The Expedition Organiser tries to put everything in place that will allow the expedition to proceed. The real success of an expedition will depend on the degree of involvement and co-operation of the expedition members. The Expedition Organiser will try to anticipate the things that may go wrong and plan for them to allow things to go smoothly. An effective Expedition Organiser will try to do this but some things, such as weather, sea conditions and visibility are beyond their control. Even the best Expedition Organiser needs the co-operation and help of the expedition members, an element of luck with the weather, and a great deal of patience.

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7.4 Selecting a Location The choice of location for an expedition will depend on a number of factors. Consider initially the level of interest or demand for an expedition and gauge how many people may want to go to a particular location. Are there enough people to make the expedition viable? It is also important to consider the amount of time available for the trip e.g. a single day trip, long weekend, week-long trip or more and what is feasible in the time. Remember that some people may be towing boats or compressors and will not be able to travel as fast as the rest of the party.

In selecting a location, consider the type of diving planned. If shore diving, plan for access to a number of good shore diving sites with easy entry and exit points within easy reach of the accommodation. Small boat diving, in RIBs, for instance, requires launching and recovery facilities. The tides in a harbour need to be confirmed as suitable: if the slipway dries out it may be extremely difficult to recover the boats. Mooring or secure overnight parking is also an important consideration. The number of boats available will determine the structure of your diving during the trip. Access to several boats will widen opportunity to go farther from the harbour to dive. The extra boat space allows more divers to be taken out on each trip as well as providing additional safety cover. A single boat at sea may be vulnerable. Hard boat diving from bigger charter boats is readily available in well known and popular dive areas throughout Scotland and the UK. Not all charter boats carry a compressor so diving should be planned around air supplies. If using a portable compressor, bear in mind that these can be very noisy, and take considerable time to fill a group of cylinders.

Considering the availability of suitable accommodation early on is vital if the planned trip is to take place on more than a single day. Without accommodation there is no trip, and arranging it can be the hardest part of the whole exercise. Booking early is important, but weekend accommodation during the summer season can be hard to find. The expedition must be affordable. Dive trips can be costly and a live aboard trip to the Red Sea or St Kilda can be quite expensive. Everyone should be made aware of the costs involved in any trip they are planning to go on.

7.5 Advance Organisation Pre-planning allows the expedition organiser to keep a check on the progress of the expedition and to anticipate what will be needed when on site. The risk assessment starts the minute the organiser begins thinking about the expedition. The following is a list of factors to consider when planning an expedition: Equipment - Boats, compressors, dive gear, mooring buoys, shot lines, decompression lines, risk assessment and dive log sheets are all examples of the type of equipment that might be considered. Is there access to enough equipment and if not, can you it be obtained? A very important consideration is how to get all the necessary equipment to the dive site; three boats and two cars with tow bars does not work!

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Weather forecasts – Before leaving on an expedition, obtain a weather forecast. This should be checked frequently with local forecasts to ensure the dive party is up-to-date with any expected changes to local weather.

Tides – Knowledge of the timing of tides is essential in predicting slack water. However, there may be variations in the timing of slack water, and gaining local knowledge may be beneficial. Dive Sites - Finding a selection of dive sites before setting off can be an advantage in identifying several potential sites for any one day. This will give some structure to plans and may help indicate what equipment will be required. A selection of dive sites will prove useful in changeable weather

Site Selection - The expedition organiser should find out as much as possible about the site. If information is limited, the first few dives should be exploratory dives with no, or minimal, decompression requirements. Aim to find out:

• Maximum depth at and around the site.

• Tides and currents experienced at the site and the best time to dive.

• Any exceptional currents, particularly the likelihood of vertical currents.

• Bottom composition and expected visibility.

• If it is a wreck dive try, to find out about the condition of the wreck.

• How other divers have dived it before.

• Location of telephones, police, recompression chambers, doctors etc. There is a greater chance of an incident on a deep dive and this information common to all dives, must be readily available on a deeper dive

Purpose of Dives - Some dive trips cannot be open to all divers. Trips involving deeper or more demanding dives require more experienced divers and are not the place for trainees or those with little experience. Fortunately, these often tend to be on a smaller scale and other more accessible dives may be able to be run around them. Some of this is common sense and some is contained in ScotSAC rules. If planning to dive a wreck at 40m, ensure all divers are suitably qualified and have relevant experience.

Access to Water – For boat diving, knowledge of the effect of tides on local launch sites will be required. For shore diving, the Expedition Organiser should obtain information on entry and exit points for each dive, the parking arrangements and whether or not permission is required to dive from that stretch of shoreline.

Shore dive, RIB, or Hard boat: which is best? In most instances the location of the site often dictates the style of the dive. All three options present the diver with a different set of risks to manage. In general, boat cover gives more protection to divers in the water, particularly if there is the possibility of currents; however, perhaps the site is suitable for shore diving and hence attractive to Branches without a boat. Shore Diving If diving from the shore, consider carefully how to support the divers in the water. Without the assistance of a boat, the divers are relying entirely on their own abilities to get back to the shore. This is especially important in the case of an emergency: could a diver recover a stricken Buddy from the water and get them to a place of safety? A suggested list of risks that should be assessed are noted below:

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• How far out would a diver surface from the deepest part of the dive?

• Can a shot line be used?

• Can stage bottles be rigged on the line?

• Can all members of the group cope with the entry to the water?

• How easy is the exit?

• Are divers adequately protected from the weather?

RIB Diving Rigid Hull Inflatable Boats are a popular choice of boat for Branches. They are popular as they are fast, manoeuvrable and easily transported by trailer and an average sized car. The use of a RIB when planning a deep dive does however require the risk/benefit analysis to be carried out. The design of the RIB and the very reasons for its popularity can actually be a handicap when deep diving as they offer limited space and shelter. Space is important as the average deep diver will carry more equipment than their sports diving companion, such that a RIB that normally carries six divers may safely carry only four deep divers. Space will also be a consideration if one of the divers becomes unwell. Shelter is important, as deep dives are often long dives, which could leave divers chilled. The wind chill from a RIB travelling at 20mph can make a 15oC spring day seem like winter. A suggested list of risks you should assess is noted below:

• How experienced is the coxswain?

• Is there enough boat space for all the equipment needed?

• How many divers can be accommodated?

• Is the site easily located?

• Can a shot line be placed on site?

• Can stage bottles be rigged to a line?

• How will the boat track the divers in the water? (SMBs, DSMBs, Surface Location Aids etc. How will the divers get back into the RIB?

• Are divers adequately protected from the weather? Hard Boat Diving The skipper is not in charge of the diving. Most skippers will do much of the risk assessment, but the divers themselves are ultimately responsible. All dive charters are now required to carry oxygen in case of emergency. However, the dive party is ultimately responsible for the emergency equipment and should not rely solely on what may be provided by the boat. Hard boats provide a larger and more stable dive platform than a RIB and in general are more suited to deep dives; however, some of risks should be assessed are noted below:

• How easy is the entry to the water?

• How easy is it to get back into the boat?

• How much protection from the weather is available?

• Emergency Contacts - The following information on emergency contacts should be

made available to everyone on the expedition: • Coastguard - which Coastguard area will you be working in and the

telephone number of the Coastguard.

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• Recompression Chamber - the location and telephone number of the nearest Recompression Facility is no longer required, as all hyperbaric treatments are co-ordinated by the National Hyperbaric Centre in Aberdeen (0845 408 6008) or the Diving Diseases Research Centre (DDRC) if in England (07831 151523).

• Telephone - The location of the nearest public telephone to the dive site or knowledge of mobile phone coverage as they do not always work well in some remote locations.

• Dive Centre / Compressor - The telephone number and location of the nearest Dive Centre or air station if applicable.

• Petrol Stations - The location and opening times of the nearest petrol station.

• Accommodation - The address and telephone number of the accommodation used by the expedition and any specific items required e.g. is linen provided?

• Dive Party Personal Information – The following information should be collected for all divers: name, address, home telephone number, qualifications and experience, next of kin. If there is a serious incident the police WILL require this information. Your Branch should already carry this information, but ensure it is available on the expedition.

• Child Protection - If a dive party includes any members under 18, additional

planning may be required to comply with the child protection guidelines. This will include parental permission and medical information, and also written permission if it is planned to take any photographs of under 18’s. Please refer to www.scotsac.com for the latest requirements.

7.6 Organisation on the Day

When the day eventually comes, the good work and advanced planning will fall into place, but there are still many tasks to complete throughout the day. On the morning of departure, a final check of local weather conditions will ensure conditions are still suitable. On arrival at he destination, the expedition organiser is responsible for liaising with boat skippers, accommodation letting agents, marina office and checking access / boat launch points as appropriate.

The risk assessment should be completed upon arrival, with any risks and control measures

communicated to all those involved. See Master Diver lecture 1 on Safety and Emergency

Procedures for further information on risk assessment. The Expedition Organiser is also

responsible for appointing other roles such as the Dive Marshall and Safety Officer.

7.7 Roles and responsibilities on an expedition The members of an expedition will go a long way to determining the sort of diving that may be undertaken. Any expedition needs a core of experienced divers who can help to “run the show” and look after the less experienced divers. Those with less experience will learn from seeing this in action and may be able to take on more responsibility in future expeditions. There is a lot to be said for not organising any expeditions until the diver has been on three or four and seen how it is done.

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An expedition comprising only less experienced divers, especially away from home waters, is going to be more restricted and potentially less safe than an expedition with a range of experience available. This does not mean that the experienced people need to do everything. Everyone can have an active role, but some will need support and supervision from those who have done it before. Dive Leaders Divers in the water operate as Buddy pairs and one of the pair is appointed as the Dive Leader. The Expedition Organiser may appoint the Dive Leaders, but often this is not necessary and it will be obvious with the pairing who is going to lead – or allow the divers to agree between them. The Dive Leader is usually the more experienced diver but the less experienced diver may wish to lead under supervision. The Dive Leader is primarily responsible for the safety of the dive. Organising dive pairs is an art form that must successfully juggle many competing desires and factors. The most common (and safest) strategy is to put the most experienced divers in with the least experienced. Other considerations may include compatible diving styles, “sprinters and dawdlers”, dry suits and wet suits, those who want to dive deep and those who don’t, the air guzzlers and those that seem not to breathe, cylinder sizes, personalities and training needs. If the planned dive is deep or technically demanding it is important that both divers in the pair are suitably experienced, prepared and built up for the dive. If more than one dive is planned in a day it is best to keep the dive pairs together for that day. They will have similar dive profiles and decompression penalties. If, for any reason, the dive pairs have to be reorganised before the divers are desaturated the dive plan for the second dive should be formulated using the greater decompression penalty of the pair. Having to reorganise dive pairs can occur quite often because it is quite unusual for every diver to dive every dive of a multi-dive expedition. Dive Marshall The main purpose of a Dive Marshall is to maintain an accurate log of the diving carried out on the expedition. This is best done by one person, especially on shore dives and hard boat diving. On a hard boat the skipper may keep a Dive Log but it is the responsibility of the Dive Marshal to keep a dive log. It is quite likely that the Dive Log will be kept by a number of different people, especially if there are several different boats being used. Dive Logs can be very difficult to keep on a RIB in rough water or bad weather and it may be necessary to rewrite them onto a master Log when back on shore. The Dive Log should provide valuable information to the members of the expedition, the Coastguard, the recompression chamber, and the Police if there is an incident. The minimum information a Dive Log should contain includes:

• Location

• Date

• Weather

• Sea conditions

• Dive pairs - names and qualifications

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• Entry and exit times

• “air in” and “air out”

• Maximum depth

• Bottom time

• Decompression / safety stops A template dive log is available to download from www.scotsac.com Safety Officer This person’s main duty is the handling and co-ordination of any incident or accident should one occur. The Safety Officer should know the emergency contacts for doctors, National Hyperbaric Centre, Coastguard and know how to contact them. The Safety Officer should complete the risk assessment sheets and inform all divers of the associated hazards. Boat Handlers When an expedition involves the use of small boats operated by members, there are three different jobs that need to be done. The first is towing the boats to and from the launch site and launching them. This obviously requires a vehicle with a tow bar. A boat handler is required to operate the boats in the water and drive to and from the dive site. Boat handlers should be appropriately qualified and have experience of picking up divers in the water. Manoeuvring boats to pick up divers calls for the utmost care and skill, and boats are driven routinely in confined water, near rocks, with people in the water. All are hazardous situations that most normal boats try to stay well clear of. Rough water and currents, especially near people in the water, rocks, or piers / slipways, call for greater skill and experience. Equipment Officer The Equipment Officer is responsible for all club equipment required by the expedition. They should ensure that the equipment gets to the dive site, and ensure its safe return. The Equipment Officer also co-ordinates any repairs that are required. Standby Divers These are divers ready to enter the water, with full kit available to hand, who remain on the surface / shore during a dive ready to assist divers in the water should an incident occur and a rescue or search become necessary. They should be suitably experienced and qualified, and have very little or no bottom time penalties from previous dives. If the party is diving in two waves, divers from the second wave can cover the first wave. Compressor Operators Compressor operators become necessary if making use of a portable compressor or a coin-operated compressor. They should understand the safety and legal requirements of compressor operation with care taken to observe test dates and cylinder working pressures. Compressors are noisy, and filling lots of cylinders can take a long time. Branch Diving Officer Ultimately, everyone in the expedition is responsible through the Expedition Officer to the Branch Diving Officer (BDO). The BDO is responsible for safety and training in the Branch and must be totally satisfied with all aspects of the diving and training carried out. Through the National Diving Officer, ScotSAC places the BDO in the position of ultimate responsibility within the Branch and the decisions they have to make at times may not be to the satisfaction of the divers affected by those decisions.

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Organisation on the Day Before leaving for the dive site, the divers should be made aware of the dive pairs. The dive pairs should be allocated to boats, if applicable, and they should now look after each other. If there are specific things to be done during a dive (training, searches, practical work etc.) it may be necessary to give people precise roles. Brief the divers about the dive site and any associated risks. Give them an idea of the dive profile and navigation plan. In its most basic form this will indicate: what the dive will look like, where they will go in, how deep they will go, which direction to swim, when to terminate the dive and so on. Remember it is a good idea to put seasick divers in with the first wave and wet suit divers in with the second (keeping them dry as long as possible). After arrival at the dive site, the first wave of divers kit up while the initial entries in the Dive Log are entered. Inform the Coastguard of the location of the dive, how many people are diving and the estimated time the diving will finish. Raise the dive flag. Never leave all the dive boats at anchor and unattended. Never leave divers without surface cover and never drive fast at a dive site when there are divers in the water; the boat handler may think he knows where they are, but can he be absolutely certain? When the divers surface, check that they are OK and help them to get out of the water. Complete the Dive Log entering the dive profile and the ‘Time Out’ and ‘Air Out’. The first wave stow their kit away and the second wave of divers kit up. Their initial details are entered in the Dive Log before they enter the water. The first wave of divers can carry out a post-dive debrief and provide cover to the divers in the water. When all divers are safely out of the water the dive details of the second wave of divers should be logged and the Coast Guard called on the VHF radio (Channel 16) to inform them that diving is completed safely and the dive flag taken down. The second wave of divers stow their kit away. Any incidents or problems during a dive should be reported to the Expedition Organiser and the Safety Officer. The divers in the second wave carry out a post-dive debrief. When back at base the dive profiles should be checked, the surface interval planned and the time of the next dive set and communicated to all members of the party. If necessary, a Master Log sheet should be rewritten. Tasks needing to be done should be delegated to members of the party. These may include mooring boats, getting fuel, filling bottles, checking and repairing kit, giving feedback or advice to less experienced members of the party, cooking meals etc. The divers should also be encouraged to complete their own Log Books. 7. 8 Delaying, Altering or Abandoning a Planned Dive Despite all of the planning and preparation that goes into a dive expedition it may become necessary to alter your plans or abandon a dive altogether if conditions or the circumstances change.

• WEATHER CHANGES - The main problem with weather when diving has to do with wind. If the wind changes in strength or direction the state of the sea can change considerably in a short space of time. It may be necessary to re-evaluate the safety of the dive plan in light of changing weather conditions. The Expedition Organiser needs to decide what to do before the weather and sea conditions get too dangerous to recover the divers already in the water. It should be remembered that what may be seen as dangerous for inexperienced divers may be quite acceptable for more

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experienced members of the party. Safety is the prime concern: if there is any doubt, the dive and the site should be re-planned.

• DIVERS NOT DIVING - During an expedition it is quite likely that not all of the divers will dive all of the dives. There may be a variety of reasons for this: they may be tired, cold, seasick, hungover, ill, or have damaged dive gear. Pulling out of a dive is always an option if the diver does not feel like it and no blame should be attached if someone does this. The Expedition Organiser simply has to re-plan the dive pairs. If too many of the more experienced divers are not diving, the viability of the dive plan may need to be re-assessed on safety grounds.

• ILLNESS OR ACCIDENT - Whether it is a diving-related accident or not, the safety and treatment of members of the expedition takes priority over all other tasks or diving. If arranging for treatment means not diving then that is what happens. If the injury was due to a diving-related incident the Expedition Organiser and the Safety Officer should ensure that the incident is fully recorded. If a diver is feeling ill or is injured but still wants to dive the Expedition Organiser or BDO has the authority to refuse permission to dive if they feel that safety may be compromised. The diver who is feeling ill should recognise the problem and make the decision to withdraw from the dive himself, but this does not always happen.

• MECHANICAL FAILURE - Mechanical failure of boats or dive gear may force a change of plan. Careful maintenance before the expedition and care in using equipment may minimise the risk, and disappointment, of failure.

• REQUESTS FOR HELP - If a request for help or assistance is received from the Coastguard or another vessel while at sea, the boat handler is duty bound to respond if he can. He cannot respond, however, if in doing so you leave your divers without cover and in danger.

7.9 Chain Of Command and Responsibility A dive expedition may appear, on the face of it, to be a discrete and self-contained unit. This is not strictly true, because the expedition operates within the structure of the Branch and the Branch operates within the structure and rules of the Scottish Sub-Aqua Club. There are, therefore, layers of responsibility and lines of communication reaching from the divers in the water right up to the Board of ScotSAC. On the ground, or in the water, the Buddy pairs are directly responsible for each other and must operate within the boundaries of safe diving practice, and the rules and recommendations of ScotSAC. Each Buddy pair is in turn responsible to the Expedition Organiser as the co-ordinator of the expedition. Each Buddy pair effectively operates under the direction and authority of the Expedition Organiser and should be responsive to the requests and the decisions they make.

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Members of the expedition taking on support roles such as boat towing, boat handling, compressor operators, Branch Instructors, Dive Marshall/Log Keepers, have a two-way obligation to operate effectively and safely. They are responsible to the Expedition Organiser who has delegated the tasks to them. They are also responsible to the other members of the Dive Expedition to ensure that the tasks are properly completed. Forgetting to put fuel in a boat, or incorrectly filling a cylinder, may ruin a dive or may compromise the safety of the divers in the water. Outwith the expedition unit, there is a responsibility to the Branch and to the Branch Diving Officer. The decisions made at Branch level provide a framework within which people dive. The expedition must adhere to the dive practice and requirements laid down by the Branch and the BDO. The training requirements and the standards of diving should be upheld and all divers should dive using the recommended safe practices for both themselves and their buddies. If necessary, the Expedition Organiser should remind the divers about depth limitations and what is expected of them. This is essential if any training carried out is to be accepted as valid. Beyond the Branch, the ScotSAC Board, the National Diving Council, and the National Diving Officer set the national framework within which we all dive. The Branch is responsible, through the Regional Coaches, to ScotSAC for the conduct and safety of its diving and dive training.

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8 Compressor Operation 8.1 Introduction This lecture introduces the main elements of a compressor and explains its function and use. 8.2 Basic features of a compressor Diving compressors are used to compress air or other gases for use in diving. Compressors may be powered using a fuel engine or electric supply and deliver compressed air directly to a diving cylinder, or to large storage cylinders, from which diving cylinders may later be filled. During the compression process the air is filtered to remove impurities, ensuring the diver always breathes the purest air available and is not harmed by any contaminants. A compressor consists of the following components:

• Motor – self-contained petrol, diesel or electric.

• Drive - usually belts and pulleys. Sometimes the crank pulley is also the cooling fan.

• Compressor body - containing the crank shaft and the lubrication system.

• Pistons - driven by the crank, inducting and compressing the air.

• Cylinders - housing the pistons and the non-return valves.

• Pressure gauges, and pressure relief valves – providing information to the operator

• Filter - takes fresh air in to compressor and must be sited well away from smokers and sources of fumes, e.g. the exhaust on fuel-powered units.

• Drain valves between stages to release any condensate, and to vent any stored pressure after use.

Physics of Compressors Charles’ Law tells us of the relationship between temperature and volume: ‘For any gas at constant volume, the pressure of the gas will vary directly with the absolute temperature.’ Therefore, during the compression of a gas, the temperature of the gas increases. Compressor Stages Consider the most basic of compressors - the bicycle pump. Even with small amounts of compression, the temperature of the gas increases. A bicycle pump compresses air using one stage meaning that the output pressure is formed in a single chamber. However, compressing air in multiple stages is more efficient and reduces the effects of heat. In each stage air is compressed by means of a piston reciprocating in a cylinder. As the piston descends, it sucks air in through a non return valve. As the piston returns, it compresses the air until it has sufficient pressure to pass through the other non return valve. Each stage boosts the pressure, and the final stage pumps air into the cylinder. In a typical diving compressor, air is compressed in three stages. Heat may be dissipated during compression using ‘intercoolers’ which are coiled copper pipes through which the air passes, with a cooling fan drawing cool air over the pipes. Multistage compressors use a decreasing physical size of stage chambers to improve efficiency. Water Separators Water moisture accumulates at each stage of compression and requires removal. Condensate is a white translucent emulsion consisting of water and tiny suspended oil droplets. Smaller compressors require the operator to drain the condensate at regular

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intervals, avoiding a build up. Larger compressors purge automatically into a reservoir. In the event of the condensate not being purged, an accumulation will backup into the previous stage, resulting in damage to the piston. More significantly, the condensate may transfer to the diving cylinder which results in contaminated air. Air Purity As the partial pressure of a gas increases at depth, the effect of any impurities also increases. Whilst we are able to tolerate small amounts of carbon monoxide at ambient pressure, at depth these effects are multiplied and may prove dangerous or fatal. It is therefore essential that the air produced by the compressor is as pure as possible. The following air purity standard is recommended and is extracted from British Standard EN 12021:

Nitrogen As in atmospheric air

Oxygen 21% ±1%

Carbon dioxide 0.05% (500ppm)

Carbon monoxide 3ppm

Oil 0.5mg/m3

Water <25mg/m3

Nitrogen dioxide < 1ppm

Nitrous oxide < 1ppm

Odour / taste None

Solid particles No residue on Millipore filter after passing 5 litres of

air

Air purity can be tested using an analysing kit. Air may be contaminated by the intake air being dirty, containing dust, smoke, fumes, carbon monoxide or water. The remedy is to site the air intake in clear clean air, away from cigarette smoke, exhaust fumes, strong smells and rain. Alternatively, the contamination can originate from inside the compressor. This is harder to deal with, and indicates mechanical problems such as poor maintenance, incorrect lubricant, overheating, or excessive wear. If oil breakdown products are the contaminants, then the compressor may be running too hot, or the wrong lubricant is being used. Nitrogen-based compounds can be produced which are unpleasant to breathe, especially at depth. If the contaminant is oil, then the pistons may be worn and a major overhaul could be required. Only oils specially formulated for compressor use should be used.

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Chemical Filters Chemical filters similar to that shown below are used in all compressors to remove a variety of impurities in the gas including carbon dioxide and carbon monoxide.

Filter Material Removes

Paper or foam Dust and insects

Felt pads Dust

Alumina Oil mist and water

Activated charcoal Oil and organic vapours

Silica gel Moisture

Molecular sieve Oil mist and water

Hopcalite Carbon monoxide

The table above illustrates the range of materials used to remove impurities from the gas. Filter material become less efficient with use, as the material becomes saturated with contaminants.

Molecular Sieve(moisture & oil)

Silica Gel or Activated Alumina

(moisture)

Felt Pad (Solids)

Activated Carbon

(oil & odour)

Felt Pad (solids)

Felt Pad (solids)

Felt Pad (solids)

Out

In In

Molecular Sieve(moisture & oil)

Silica Gel or Activated Alumina

(moisture)

Felt Pad (Solids)

Activated Carbon

(oil & odour)

Felt Pad (solids)

Felt Pad (solids)

Felt Pad (solids)

OutOut

In InIn

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8.3 How a compressor works

• Power from the engine is supplied to the compressor through a shaft or belt system.

• Air is drawn through a primary filter, removing large particles.

• The first stage compresses air from ambient pressure to an intermediate pressure (normally 50-85 bar).

• The air also passes through a cooler and water separator, removing any moisture.

• Further stages compress to the maximum operating pressure of the compressor, for example 240 – 300bar.

• Water separators and coolers exist during each stage. Air is passed through the chemical filter after the final stage, removing impurities listed above.

• Compressed gas is delivered to the diving cylinder, or storage cylinder via a pressure gauge and hose.

•

Storage Cylinder

Chemical Filter

Water separator

Cooler Water separator

Manifold

Gauge

Cylinder feed hoses and clamps

Power from engine

Gauge

3rd stage

Water separator

Cooler

1st stage

Filter

Air in

2nd stage

Gauge

Storage CylinderStorage Cylinder

Chemical Filter

Water separator

Chemical Filter

Water separatorWater separatorWater separator

Cooler Water separator

Cooler Water separator

Cooler Water separatorWater

separator

Manifold

Gauge

Cylinder feed hoses and clamps

Manifold

Gauge

Cylinder feed hoses and clamps

Manifold

Gauge

Cylinder feed hoses and clamps

Power from engine

Gauge

3rd stage

GaugeGauge

3rd stage3rd stage3rd stage

Water separatorWater

separatorWater

separator

CoolerCoolerCooler

1st stage1st stage1st stage1st stage

Filter

Air in

Filter

Air in

2nd stage

Gauge

2nd stage2nd stage2nd stage2nd stage

GaugeGauge

8.4 Compressor Log Maintaining an accurate log of compressor running times is important to ensure the compressor is continues delivering air of the appropriate standard. A typical log will include:

• Date

• running time

• operator

• number of cylinders filled

• faults reported

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8.5 Typical Compressor Operation

• Check oil levels of compressor and engine

• Check fuel level in engine (where applicable)

• Check compressor log to see if filter needs to be changed

• Position compressor in open atmosphere away from fumes

• Open drain valves, start compressor

• Close drain valves and allow pressure to build up

• Check cylinder test date and working pressure

• Connect cylinder

• Purge drain valves regularly

• At working pressure, close the cylinder and feed, then vent the high pressure before disconnecting

• Open drain valves and allow compressor to run briefly

• Switch off and complete log, reporting any faults 8.6 Types of Compressors Portable compressors are a useful addition to many Branches as they can be transported to dive sites, alleviating the need to visit dive shops. However, due to their size, they take longer to fill cylinders than the larger fixed compressors found in dive outlets. Fixed compressors have a larger capacity and are usually based in larger diving retailers. They may be located remotely from the air panel; for example in the back of the dive shop. Many fixed compressors in larger outlets have storage banks to cope with fluctuations in filling demand throughout the day.