Health, Safety and the Environment CGE653

Ir. Dr. MOHD SHIRAZ ARIS

Hazard Identification and Risk Assessment

HSE

Fundamentals Principles Tools Application/

effects

Fire, Explosion, Toxicity,

Exposure, Environmental

impact

HAZIDHAZOPHIRARC

Measurements/data/learnings

Hazard and Risks• Hazard - a danger or risk?

• Hazard - source of potential damage, harm or adverse health effects/asset losses

• Hazard - condition or set of circumstances presenting a potential for harm

• Categories - health and safety (OSHA)

Hazard and Risks

• Risk - chance or probability of harm/loss if exposed to a hazard

• Risk assessment - a systematic process of evaluating the potential risks that may be involved in a projected activity

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Hazard Identification and Risk Assessment Methodologies

Faculty of Chemical Engineering Universiti Teknologi MARA

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Hazard and Risk: Recap From Chapter 1

▪ Hazard = a condition that has the potential to cause human injury or fatality, damage to property, damage to the environment or some combination of these.

▪ Risk = a measure of human injury, environmental damage, or economic loss in terms of both the incident likelihood and the magnitude of the loss or injury.

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For each industrial process, the following questions must be asked:

– What are the hazards? – What can go wrong? – What are the chances? – What are the consequences?

Risk Assessment

Hazard Identification

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Introduction

• Hazard Identification and Risk assessment are sometimes combined into a general category called hazard evaluation/ hazard analysis.

• Can be done at any stage during the initial design or ongoing operation or process.

• The results of a hazard analysis are: • The identification of unacceptable risks and

• The selection of means of controlling or eliminating them

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Hazard identification and risk assessment procedureSystem Descriptions

Hazards Identification

Risk determination

Risk and/or hazard

acceptance

Build and/or operate system

Modify system/ process

Scenario Identification

Accident consequenceAccident probability

Yes

No

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Process Hazard Analysis (PHA)

Process Hazard Analysis

What are the Hazards?

What can go wrong?

How likely it is?

What are the consequences?

FOUNDATIONS FOR PROCESS HAZARD ANALYSISHistorical

ExperiencesPHA

MethodologyKnowledge and

Intuition

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Process Hazard Analysis (PHA)• PHA allows us to:

• Determine types and locations of potential safety problems • Identify corrective measures to improve safety • Preplan emergency actions to be taken if safety controls

fail • It must address

• The hazards of the process

• Engineering and administrative controls applicable to the hazards and their interrelationship

• Consequences of failure of engineering and administrative controls, especially those affecting employees

• The need to promptly resolve PHA findings and recommendations.

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PHA Methodology

• Process Hazards Checklists • What-if Analysis • Failure Modes and Effects Analysis (FMEA) • Fault Tree Analysis (FTA) • Event Tree Analysis (ETA) • Hazard and Operability (HAZOP) Analysis

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Process Hazard Checklist

• It is simply a list of possible problems and areas to be checked.

• The list reminds the reviewer or operator of the potential problem areas.

• Can be used during the design of a process to identify design hazards, or it can be used before process operation.

• A systematic approach built on the historical knowledge included in checklist questions.

• Applicable to any activity or system, including equipment issues and human factors issues

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A classic example: automobile checklist

• Check oil in engine • Check air pressure in tires • Check fluid level in radiator • Check air filter • Check fluid level in windshield

washer tank • Check headlights and taillights • Check exhaust system for leaks • Check fluid levels in brake system • Check gasoline level in tank

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Example of process safety checklist

EQUIPMENT DESIGN 1. Design correct for maximum operating pressure? 2. Corrosion allowance considered? 3. Special isolation for hazardous equipment? 4. Guards for belts, pulleys and gears? 5. Dikes for any storage tanks? 6. Construction materials compatible with process

chemicals? 7. Emergency standby equipment needed? 8. Relief valves or rupture disks required? 9. Emergency valves readily accessible? 10. Special explosion proof electrical fixtures required?

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Advantages of safety checklist

• Is quick and simple to perform and is easily understood.

• Makes use of existing experience and knowledge of previous systems.

• Helps check compliance with standard practice and design intention.

• Ensures that known hazards are fully explored.

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Limitations of safety checklist

• Highly dependent upon the quality of the prepared checklist.

• May not be comprehensive and is likely to miss some potential problems. ▪ The structure of checklist analysis relies exclusively on

the knowledge built into the checklists to identify potential problems.

▪ The analysis is likely to overlook potential new hazards.

• Traditionally only provides qualitative information. ▪ Most checklist reviews produce only qualitative results,

with no quantitative estimates of risk-related characteristics.

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What if Analysis

• What-if analysis is a brainstorming approach (beginning with what if question) that uses broad, loosely structured questioning to • postulate potential upsets that may result in accidents

or system performance problems and • ensure that appropriate safeguards against those

problems are in place. • A systematic, but loosely structured, assessment

relying on a team of experts brainstorming to generate a comprehensive review and to ensure that appropriate safeguards are in place

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What if Analysis

• Typically performed by one or more teams with diverse backgrounds and experience that participate in group review meetings of documentation and field inspections

• Applicable to any activity or system • Used as a high-level or detailed risk assessment

technique • Generates qualitative descriptions of potential

problems, in the form of questions and responses, as well as lists of recommendations for preventing problems

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What if Analysis

• The quality of the evaluation depends on the quality of the documentation, the training of the review team leader, and the experience of the review teams

• Generally applicable for almost every type of risk assessment application, especially those dominated by relatively simple failure scenarios

• Occasionally used alone, but most often used to supplement other, more structured techniques (especially checklist analysis)

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Examples of what if analysis

• Equipment failures: ▪ What if ……. the valve leaks?

▪ What if ……. the alarm malfunction?

▪ What if ……. the pressure regulator fails? • Human errors: ▪ What if ……. operator fails to re-start pump?

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Limitations of what if analysis

• Likely to miss some potential problems. • The loose structure of what-if analysis relies exclusively on the

knowledge of the participants to identify potential problems. • If the team fails to ask important questions, the analysis is likely

to overlook potentially important weaknesses. • Difficult to audit for thoroughness.

• Reviewing a what-if analysis to detect oversights is difficult because there is no formal structure against which to audit.

• Reviews tend to become "mini-what-ifs," trying to stumble upon oversights by the original team.

• Traditionally provides only qualitative information. • Most what-if reviews produce only qualitative results; they give

no quantitative estimates of risk-related characteristics. • This simplistic approach offers great value for minimal

investment, but it can answer more complicated risk-related questions only if some degree of quantification is added.

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Failure Modes and Effects Analysis (FMEA)

• FMEA is a qualitative reasoning approach best suited for reviews of mechanical and electrical hardware systems.

• The FMEA technique (1) considers how the failure modes of each system component can result in system performance problems and

(2) ensures that appropriate safeguards against such problems are in place.

• A quantitative version of FMEA is known as failure modes, effects, and criticality analysis (FMECA).

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Failure Modes and Effects Analysis (FMEA)

• A systematic, highly structured assessment relying on evaluation of component failure modes and team experience to generate a comprehensive review and ensure that appropriate safeguards against system performance problems are in place

• Used as a system-level and component-level risk assessment technique

• Applicable to any well-defined system

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Failure Modes and Effects Analysis (FMEA)

• Sometimes performed by an individual working with system experts through interviews and field inspections, but also can be performed by an interdisciplinary team with diverse backgrounds and experience

• A technique that generates qualitative descriptions of potential performance problems (failure modes, causes, effects, and safeguards) as well as lists of recommendations for reducing risks

• A technique that can provide quantitative failure frequency or consequence estimates

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Failure Modes and Effects Analysis (FMEA)

• Used primarily for reviews of mechanical and electrical systems, such as fire suppression systems and vessel steering and propulsion systems

• Used frequently as the basis for defining and optimizing planned equipment maintenance because the method systematically focuses directly and individually on equipment failure modes

• Effective for collecting the information needed to troubleshoot system problems

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Example of FMEA on a heat exchanger

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Limitations of FMEA

• Examination of human error is limited. • A traditional FMEA uses potential equipment failures

as the basis for the analysis. All of the questions focus on how equipment functional failures can occur.

• Focus is on single-event initiators of problems. • A traditional FMEA tries to predict the potential

effects of specific equipment failures. • These equipment failures are generally analyzed one

by one, which means that important combinations of equipment failures may be overlooked.

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Limitations of FMEA• Examination of external influences is limited.

• A typical FMEA addresses potential external influences (environmental conditions, system contamination, external impacts, etc.) only to the extent that these events produce equipment failures of interest.

• External influences that directly affect vessel safety, port safety, and crew safety are often overlooked in an FMEA if they do not cause equipment failures.

• Results are dependent on the mode of operation. • The effects of certain equipment failure modes often vary widely,

depending on the mode of system operation. • A single FMEA generally accounts for possible effects of equipment

failures only during one mode of operation or a few closely related modes of operation.

• More than one FMEA may, therefore, be necessary for a system that has multiple modes of operation.

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Fault Tree Analysis (FTA)

• Originated in the aerospace industry. • Used extensively in the nuclear power industry. • Becoming more popular in the chemical process

industries. • Provides a traceable, logical, quantitative

representation of causes, consequences and event combinations.

• Top-down approach • Starts with a well-defined event (top event) and

works backwards to identify the causes of the top event.

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Logical Functions in FTA

1. Top Event and Intermediate Events

▪ The rectangle is used to represent the TOP event and any intermediate fault events in a fault tree.

▪ The TOP event is the accident that is being analyzed. Intermediate events are system states or occurrences that somehow contribute to the accident.

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Logical Functions in FTA

2. Basic Event

▪ The circle is used to represent basic events in a fault tree.

▪ It is the lowest level of resolution in the fault tree.

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Logical Functions in FTA

3. Undeveloped Event

▪ The diamond is used to represent events that cannot be developed further in the fault tree due to the lack of suitable information.

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Logical Functions in FTA

4. AND gate

▪ Used when the resulting output event requires the simultaneous occurrence of all input events.

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Logical Functions in FTA

5. OR gate

▪ Used when the resulting output event requires the occurrence of any individual input event.

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Example of FTA – Flat Tire

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Example of FTA – Hot Water Heater Explodes

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Minimal Cut Sets• The minimal cut sets are the various sets of events

that could lead to the top event. • Some of the minimal cut sets have a higher

probability than others. • For instance, a set involving just two events is

more likely than a set involving three. • The higher probability sets are examined carefully

to determine whether additional safety systems are required.

• AND gate increase the number of events in the cut sets, whereas OR gates lead to more sets.

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Quantitative FTA• Quantitative FTA determines the probability of the

tope event. • Probability versus Reliability • Reliability = 1 – Probability • Probabilities are multiplied across an AND gate. • Reliabilities are multiplied across and OR gate.

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Example of Quantitative FTA

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Event Tree Analysis (ETA)

• A bottom-up approach • ETA begin with an initiating event and work toward

a final result. • Provide information on how a failure can occur and

the probability of occurrence. • Explore how safeguards and external influences,

called lines of assurance, affect the path of accident chains.

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Example of ETA

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ExampleCompany A produce liquefied petroleum gas (LPG) from a mixture of hydrocarbon gases. LPG is highly used as a fuel in heating appliances and vehicles. LPG tanks are installed with pressure controllers and high pressure alarms. The relief valves on top of the tanks are designed to vent of excess gas in order to prevent the tanks from rupturing. The high pressure alarms will alert the operators to take necessary action to bring the plant back to normal conditions or to shut down the plant. One of the possible incident scenario is that accidental spilt of hydrocarbons may ignite and the resulting fire may heat and LPG tank thus increasing its temperature and pressure.

Construct and event tree analysis and identify four possible outcomes that may arise from the accidental spillage of hydrocarbons.

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Initiating Event

Fire from the accidental

spillage of H/C

Level of Assurance

HP alarm alerts operator

Operator notice HP

Relief Valve operate

Operator s/d reactor

Outcome

Yes

No

Cont. operation

S/down

Tank rupture (explosion)

S/down

Cont. operation

Vapor release

S/down

Explosion

Yes

Yes

Yes

No

Yes

Yes

Yes

Yes

No

No

No

No

No

No

Explosion

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HAZOP

• This technique uses a systematic process to (1) identify possible deviations from normal operations and (2) ensure that appropriate safeguards are in place to help prevent accidents.

• a systematic process carried out by a team and involve brain-storming.

• Before a HAZOP is carried out, detailed information on the process must be available. This include, process flow diagram (PFD), piping & instrumentation diagram (P&ID), equipment specifications, materials of construction, mass & energy balances.

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HAZOP

• This technique uses special guidewords such as: • NO

• MORE

• HIGHER

• LESS

• The guidewords are combined with process parameters (e.g. speed, flow, pressure etc.) to systematically consider all credible deviations from normal conditions. For example: • MORE FLOW

• HIGHER TEMPERATURE

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HAZOP

NORMAL OPERATION (e.g. normal feed flow rate into a reactor

Deviation 1

Deviation 2

Deviation 3

Deviation 4

Potential Accident

Potential Accident

Potential Accident

Potential Accident

Guideword + Process Parameter = Deviation“LESS” + “FLOW” = “ LESS FLOW”

“MORE” + “FLOW” = “ MORE FLOW”

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Step 1 in HAZOP: Choose a study node

• A node is a specific location in the process in which the deviations of the process/design intention are evaluated. ▪ Example might be: separator, heat exchanger, scrubber,

pump, compressor, pipeline, etc. • Design/process intent is how a study node is

expected or required to behave. ▪ For example: A reactor is designed to operate between

300 to 360 °C, OR

▪ Cooling water is expected to continuously flow inside a cooling coil

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Step 1 in HAZOP: Choose a study node

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Step 2 in HAZOP: Pick a Process Parameter

• Example: • Flow

• Level • Temperature

• Pressure

• Concentrations

• pH

• Agitation

• State (solid, liquid, or gas) • Volume

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Step 3 in HAZOP: Apply a guideword

Guidewords Meaning

NO, NOT, NONE The complete negation of the intention

MORE, HIGHER, GREATER

Quantitative increase (temperature, flow rate, heating, reaction).

LESS, LOWER Quantitative decrease (temperature, flow rate, heating reaction)

AS WELL AS Intentions are achieved along with some additional activity, such as contamination.

Guidewords Meaning

PART OF Only some of the design intentions are achieved.

REVERSE The logical opposite of

OTHER THAN Complete substitution

SOONER THAN Too early or in the wrong order

LATER THAN Too late or in the wrong order

WHERE ELSE In additional locations

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Step 3 in HAZOP: Apply a guide word

• Some combinations of guide words and process parameters are meaningless. • For example: NO TEMPERATURE; PART OF PRESSURE;

REVERSE PRESSURE • The guide words AS WELL AS, PART OF, and OTHER

THAN can sometimes be conceptually difficult to apply.

• The guide words SOONER THAN, LATER THAN, and WHERE ELSE applicable to batch processing.

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Step 4 in HAZOP: Determine possible causes

• Some Possible Causes of NO FLOW: • No reactant in the intermediate storage

• Pump breaks down • Line blockage

• Line fracture

• Isolation valve closed in error

• Some Possible Causes of LESS FLOW: • Partial blockage

• Defective pump

• Density or viscosity changes

• Leaking

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Step 4 in HAZOP: Determine possible causes

• Some Possible Causes of HIGH FLOW: • Increased pumping capacity • Increased suction pressure • Control faults • Running multiple pumps

• Some Possible Causes of REVERSE FLOW: • Defective one way (check) valve • Incorrect pressure differential • Pump reversed

• Two way flow

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Step 4 in HAZOP: Determine possible causes

• Some Possible Causes of HIGH LEVEL: • Outlet isolated or blocked • Faulty level measurement • Inflow or outflow control failure • Pressure surge

• Some Possible Causes of LOW LEVEL: • Inlet flow stops

• Leak

• Control failure

• Faulty level measurement

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Step 4 in HAZOP: Determine possible causes

• Some Possible Causes of HIGH PRESSURE: • Relief valve isolated • Boiling • Incorrect vent set pressure for vents • Surge problem

• Possible Causes of LOW PRESSURE: • Generation of vacuum conditions

• Undetected leakage

• Gas dissolving in liquid

• Restricted pump/compressor line

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Step 4 in HAZOP: Determine possible causes

• Some Possible Causes of HIGH TEMPERATURE: • Fouled or failed heat exchanger tubes • Cooling water failure • Internal fire • Faulty instrumentation and control

• Possible Causes of LOW TEMPERATURE: • Fouled or failed heat exchanger tubes

• Loss of heating

• Faulty instrumentation and control

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Step 5 in HAZOP: Evaluate the consequences of the deviation

• CONSEQUENCES may both comprise process hazards and operability (e.g. shut down) problems.

• More CONSEQUENCES may results from one CAUSE. • In turn, one CONSEQUENCE can have several CAUSES.

Consequence of LESS LEVEL in V-40

▪ V-40 empty leading to pump P-8 running dry

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Final Step in HAZOP

• Recommend action • What?

• By whom

• By when? • It is at this stage that consequences and associated

safeguards are considered. • Action falls into two groups:

• Actions that remove the cause

• Actions that mitigate or eliminate the consequences. • RECORD ALL THE INFORMATION !!!!

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Sample of HAZOP Worksheet

HAZOP - Floatation systemA floatation system is commonly applied to remove oil or impurities in a water management process line-up. In an offshore produced water process floatation technology is often installed after the de-oiling hydrocyclone and bulk separation module to reduce the OIW content from approximately 1000 ppm to 50 ppm. The technology utilizes field gas in an injection port to generate micro-bubbles which will then transport oil/emulsion to the liquid surface. A skimming procedure will need to be carried out to remove the rejects into a sludge stream for subsequent onshore disposal.

production deck

1000 ppm

50 ppm

HC gas

sludge removal/oil retrieval

HAZOP - Floatation systemPerform a HAZOP to identify five (5) deviations from a design intent described above. For each of the deviations, propose the possible causes, consequences and actions required (if any). As an additional requirement, you are asked to construct a fault tree diagram for the top event for fire or explosion in the CFU.

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Item Study node Process Parameters

Deviations (guide words)

Possible causes Possible consequences Action required

1A

1B

CFU

CFU

Flowrate (1)

Flowrate (2)

Pressure

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Limitations of HAZOP

• Requires a well-defined system or activity • To apply the HAZOP guidewords effectively and to

address the potential accidents that can result from the guide word deviations, the analysis team must have access to detailed design and operational information.

• Tedious to apply and time consuming. • Focuses on one-event causes of deviations

• The HAZOP process focuses on identifying single failures that can result in accidents of interest.

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Risk Assessment

• Risk can be assessed either qualitatively or quantitatively.

• Risk is considered proportional to the expected losses which can be caused by an event and to the probability of this event. The harsher the loss and the more likely the event, the greater the overall risk.

Risk = (Probability of Accident) x (losses per accident)

The probability is normally assessed by the frequency of the past similar events.

Risk = Likelihood x Severity

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Risk Assessment

• Probability of a failure occurrence = 1/10,000

• Consequence of the failure = RM5 million

• Risk = RM5 million x 10-4

= RM50,000.00

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We cannot eliminate risk entirely. Every industrial process has a certain amount of

risk associated with it.

We have to decide if the risks are “acceptable”.

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What is ALARP?• Many regulatory authorities require that risks should be

within acceptable limits and As Low As Reasonably Practicable (ALARP).

• To demonstrate that risks are ALARP, one must show that enough has been done to reduce risks.

• In cases where the risks are well-defined, it is sufficient to show that recognized “good practices” have been implemented.

• In more complex situations, i.e., where the technology is new, to demonstrate risks are ALARP, one should show that all reasonably practicable risk reduction measures have been implemented.

ALARP• Benchmarking tool

• Associates cost of doing business

• Identifies future investments

• Positions organizations on a global scale

Ris

ks

Tech

ALARP

PIlot

Today

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Why Risk Assessment is Important?

• Risk assessment helps to: • create awareness of hazards and risks, • identify who may be at risk (employees, cleaners,

visitors, contractors, the public, etc), • determine if existing control measures are adequate or

if more should be done, • prevent injuries or illnesses • prioritize hazards and control measures.

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How Risk Assessment is Conducted?

• Assessments should be done by a competent team of individuals who have a good working knowledge of the workplace.

• In general, to do an assessment, you should: ▪ identify hazards

▪ evaluate the likelihood of an injury or illness occurring, and its severity,

▪ consider normal operational situations as well as non-standard events such as shutdowns, power outages, emergencies, etc.,

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How Risk Assessment is Conducted?

• When doing an assessment, you must take into account: • the methods and procedures used in the processing,

use, handling or storage of the substance, etc.. • the actual and the potential exposure of workers

• the measures and procedures necessary to control such exposure by means of engineering controls, work practices, and hygiene practices and facilities.

• By determining the level of risk associated with the hazard, the employer and the joint health and safety committee can decide whether a control program is required.

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How Do You Know If a Hazard is Serious?

• product information / manufacturer documentation, • health and safety material about the hazard such as

material safety data sheets (MSDSs), or other manufacturer information,

• past experiences (workers, etc), • legislated requirements and/or applicable standards, • industry codes of practice / best practices, • information from reputable organizations, • results of testing (atmospheric, air sampling of

workplace, biological, etc), • the expertise of occupational health and safety

professionals, • information about previous injuries, illnesses, "near

misses", accident reports, etc.

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What options exist to rank or prioritize risks?

• One option is to use a table similar to the following as established by the British Standards Organization:

Table 2Risk Assessment by the British Standards Organization

Likelihood of Harm Severity of Harm

Slightly Harm Moderately Harm Extremely Harm

Very unlikely Very low risk Very low risk High risk

Unlikely Very low risk Medium risk Very high risk

Likely Low risk High risk Very high risk

Very likely Low risk Very high risk Very high risk

Note: These categorizations and the resulting asymmetry of the matrix arise from the examples of harm and likelihood illustrated within the British Standard. Organizations should adjust the design and size of the matrix to suit their needs.

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Definitions for Likelihood of Harm?

• Very Likely - Typically experienced at least once every six months by an individual.

• Likely - Typically experienced once every five years by an individual.

• Unlikely - Typically experienced once during the working lifetime of an individual.

• Very unlikely - Less than 1% chance of being experienced by an individual during their working lifetime.

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Definitions for Severity of Harm?

• Slightly harmful (e.g., superficial injuries; minor cuts and bruises; eye irritation from dust; nuisance and irritation; ill-health leading to temporary discomfort)

• Moderately harmful (e.g., lacerations; burns; concussion; serious sprains; minor fractures; deafness; dermatitis; asthma; work-related upper limb disorders; ill-health)

• Extremely harmful (e.g., amputations; major fractures; poisonings; multiple injuries; fatal injuries; occupational cancer; other severely life shortening diseases; acute fatal diseases)

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Definition for Risk Level

• Very low - These risks are considered acceptable. No further action is necessary other than to ensure that the controls are maintained.

• Low - No additional controls are required unless they can be implemented at very low cost (in terms of time, money, and effort). Actions to further reduce these risks are assigned low priority. Arrangements should be made to ensure that the controls are maintained.

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Definition for Risk Level

• Medium – ▪ Consideration should be as to whether the risks can be

lowered, where applicable, to a tolerable level and preferably to an acceptable level, but the costs of additional risk reduction measures should be taken into account.

▪ The risk reduction measures should be implemented within a defined time period.

▪ Arrangements should be made to ensure that controls are maintained, particularly if the risk levels area associated with harmful consequences.

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Definition for Risk Level • High - Substantial efforts should be made to reduce

the risk ▪ Risk reduction measures should be implemented

urgently within a defined time period and it might be necessary to consider suspending or restricting the activity, or to apply interim risk control measures, until this has been completed. ▪ Considerable resources might have to be allocated to

additional control measures. ▪ Arrangements should be made to ensure that controls

are maintained, particularly if the risk levels are associated with extremely harmful consequences and very harmful consequences.

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Definition for Risk Level

• Very high - These risk are unacceptable. ▪ Substantial improvements in risk control measures are

necessary so that the risk is reduced to a tolerable or acceptable level.

▪ The work activity should be halted until risk controls are implemented that reduces the risk so that it is no longer very high. If it is not possible to reduce the risk, the work should remain prohibited.

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Another Option

• Using Hazard Risk Assessment Matrix that is derived from MIL-STD-882B.

• The hazard level consists of one number and one letter. • The number represents the severity of the event.

• 1: Death, system loss, or irreversible environmental damage; • 2: Severe injury, occupational illness, major system damage, or

reversible severe environmental damage; • 3: Injury requiring medical attention, illness, system damage,

or mitigatible environmental damage; • 4: Possible minor injury, minor system damage, or minimal

environmental damage.

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Another Option

• The letters represent: • A: Expected to occur frequently; • B: Will occur several times in the life of an item; • C: Likely to occur sometime in the life of an item; • D: Unlikely, but possible to occur in the life of an item; • E: So unlikely, it can be assumed occurrence may not

be experienced.

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Another Option

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HIRARC

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HIRARC

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HIRARC

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HIRARC