Introduction to sterilization...Types of sterilization media High Heat • Dry heat • Moist steam Low Heat • Ethylene Oxide (ETO) • Formaldehyde • Hydrogen peroxide vapour

company profile and product range

General Introduction

Introduction to sterilization


Course content and objectives

This course is composed of different modules which may be presented in their

entirety or separately with users gaining an understanding of:

1. How sterilization is just 1 step in instrument reprocessing

2. What sterilization is

3. Why steam is the most widely used sterilant

4. Critical factors that affect sterilization efficacy

5. How steam sterilizers work

6. Tests and cycles on an autoclave

7. Monitoring sterility of goods

8. Avoiding common problems associated with sterilizers


DIN Sterilization containers

In addition to standard containers in pictures:

• Longer containers for endoscopy (low temp sterilization mostly)

• Non standard sizes from some orthopaedic implant companies

• Mini containers for microsurgery 300 x 132 x 25mm

Pictures courtesy of KLS martin

Linen only


Baskets in standard containers

Pictures courtesy of KLS Martin


Part 1.

Sterilization - just 1 step in reprocessing


Sterilization - just 1 step in instrument reprocessing

Every chain is only

as strong as its

weakest link


Sterilization and ISO 17664: 2004

ISO 17664:2004 specifies the information to be provided by the medical device

manufacturer on the processing of medical devices claimed to be resterilizable, and

medical devices intended to be sterilized by the processor…so that the medical device

can be processed safely and will continue to meet its performance specification.

• Requirements are specified for processing that consists of all or some of the following

activities:

• a) preparation at the point of use;

• b) preparation, cleaning, disinfection;

• c) drying;

• d) inspection, maintenance and testing;

• e) packaging;

• f) sterilization;

• g) storage.

Before sterilizing any medical device, CSSD staff need to ensure that they follow correct protocols for reprocessing device

and selecting appropriate equipment, sterilant

media and cycle


Part 2.

What is sterilization ?


Infection control levels

• Cleaning – removal dirt and other soils

without killing microorganisms or spores

• Disinfection Destruction of pathogenic

microorganisms, but not bacterial spores.

• Sterilization – process capable of destroying

all microbial life including bacterial spores.


Sterilization and probability

Sterilization definition

An act of destroying all forms of life on and in an object including bacteria,

viruses, spores, and fungi. A substance is sterile, from a microbiological point

of view, when it is free of all living microorganisms

ANSI/AAMI ST46 Note: In a sterilization process, the nature of microbial death

is described by an exponential function. Therefore, the presence of

microorganisms on any individual item can be expressed in terms of probability.

While this probability can be reduced to a very low number, it can never be

reduced to zero.


Geobacillus stearothermophilus spores are most commonly used to test sterilization cycles

effectiveness as they are:

• Resistant to steam sterilization

• Readily commercially available and cost effective

• Not a danger to human health

• A common methodology is to quote a D value which is the time taken to reduce the spore

population by 90% or by 1 log. A 6 log reduction of a million spores is calculated as follows

assuming 1,000,000 spore initial contamination:

• 1,000,000 spores x 10% = 100,000 spores

• 1,00,000 spores x 10% = 10,000 spores

• 10,000 spores x 10% = 1,000 spores

• 1,000 spores x 10% = 100 spores

• 100 spores x 10%= 10 spores

• 10 spores x 10%= 1 spore

Measuring sterilization effectiveness

6 log reduction from 1,000,000 to 1 spore


106 105 104 103 102 101 100 10-1 10-2 10-3 10-4 10-5 10-6

0 1 2 3 Mins.

No

. o

f M

icro

-org

an

ism

s

Assumed Bioburden of 106 Micro-organisms

SAL 10-6

Minimum of 1 Min.

Safety Time

Reduction of spore survivors

Likelihood of 1 spore surviving

Log reduction example


Spaulding 1957 Classification

(traditional view)

Why are Spores difficult to kill ? Vegetative Bacteria can sporolate when threatened by a lack of water or nutrient. During sporulation they form a resistant shell that is difficult to penetrate by sterilization media. They can survive in this dormant state for long periods without water or nutrients Anthrax spores can survive over 50 years in nature under dry conditions


1. It is important to remove infectious microorganisms and organic matter that

can cover and protect these microorganisms

2. Removal of infectious microorganisms is needed to ensure that during

sterilization, the sterilizing agent can comes into contact with the entire

surface area of every medical device being reprocessed for the specified

time and temperature

Organic matter such as blood

Surface

Infectious Microorganisms

“If it's not clean...it can't be sterile” - (Spaulding)


Not always visible to the naked eye

• Handling by staff in the clean room during

inspection and packing, significantly

increased protein deposition on

instruments. Whilst this does not cause an

immediate problem, subsequent

sterilization binds proteins that assist in

gradual soiling build up overtime (summary

from Howlin 2009)

Damage and scarring of instruments

creates a surface with greater

resistance to decontamination with

subsequent build up of soiling over

time likely to lead to ineffective

sterilization (summary from Howlin 2009)

blade tip

Magnified box instrument joint

Note: Steelco offers a range of stereo viewers to aid inspection


Prions a new science

Prions Discovered in 1982 by Stanley

Prusiner, prions are unique in their ability to

reproduce on their own and become infectious.

They are different to other molecular

structures as they do not contain any

genetic DNA or RNA material and appear to

be misfolded proteins They are associated

with degenerative brain diseases where the

brain assumes a spongy characteristic

Diseases responsible for Creutzfeldt- Jakob

Disease (CJD) but also possibly Alzheimer,

and Parkinson’s disease in humans

Transmission Readily transmissible through:

brain, spinal cord , eye and pituitary gland

matter on contaminated instruments even

from a single prion

(University of Utah)

bottom picture shows

typical spongy

characteristic of CJD

infected brain tissue


Sterilization has been found to provide a 3 log 10 reduction for prions with

following technologies:

• Steam autoclave at 134°C for 18 minutes

• Steam autoclave at 121°C for 30 minutes

• Hydrogen peroxide gas plasma

• Radio frequency gas plasma

• Vaporised hydrogen peroxide 1.5-2 mg/L

(Summary from Mutala and Weber )

As it has been found that seemingly denatured proteins can be reactivated and that

sterilization only achieves a 3 log reduction, it is vital that pre-cleaning and cleaning

/disinfection of any suspected prion infected instruments is undertaken with a detergent

with approved prionicidal claim. Where possible single use instruments should be used

and disposed of

How do you kill something that

does not appear alive and differs

from normal molecular biology?

1. Inactivation through denaturation

2. Ensuring removal from surface

Dealing with prions


Keep instruments moist

Effective manual leaning (when recommended)

Effective automated cleaning

Effective sterilization

Need for effective processes at

each stage to achieve acceptable

overall log reduction

Cumulative log reduction

Important not to add

contamination during

packing in clean area

Need for appropriate sterile

barrier packaging


Part 3.

Why steam is the most widely used sterilant


Types of sterilization media

High Heat

• Dry heat

• Moist steam

Low Heat

• Ethylene Oxide (ETO)

• Formaldehyde

• Hydrogen peroxide vapour (VHP)

• Gas plasma

Steam - moist heat is used to reprocess 80 -90% of instruments in a CSSD as it is: • Proven technology • Readily available • Environmentally safe • Cost effective

However high temperatures required are not suitable for thermo sensitive instruments or endoscopes


Requirements for effective steam sterilization

1. Temperature

2. Time

3. Correct moisture level / saturation

4. Air removal

5. Direct steam contact

6. Drying

7. Appropriate sterile barrier

9. Correct loading of goods


Part 4.

Critical factors that affect sterilization efficacy


Laws of physics

• The amount of energy stored in steam is much

higher than the amount of energy stored in dry

air. (That is why you can put your hand in a hot oven

without touching sides but not in boiling water )

• Energy needed to heat water from 0°C to 100°C =

419Kj/kg or 180btu/lb

• It takes approximately 5 x more energy to create

100°C steam from 100°C boiling water at

atmospheric pressure

• Direct contact between surface of the object to

be sterilized and direct steam is required.


Steam quality

The quality of steam has a direct impact on it’s ability to inactivate by denaturing proteins

Saturated steam is the maximum of

moisture that steam can hold without liquid condensate being present. Water content needs to be 2-5%. Once all the water is vaporized, any subsequent addition of heat raises the steam’s temperature. Steam heated beyond the saturated steam level is called superheated steam. It has a poor heat transfer capacity, even though it is hotter than saturated steam and contains more energy

Heat transfer capacity of steam

Saturated steam and pressure


Time and temperature

Sterilization time using saturated steam

0.13 mins

at 140°C

0.9 mins

at 132°C

12 mins

at 121°C

80 hours

at 100°C

321 hours

at 80°C

643 hours

at 63°C

Saturated steam contains the maximum amount of water without

liquid condensate


Part 5.

How steam sterilizers work


93/42/EEC and its revised versions – European Directive for Medical Devices

97/23/EC – Pressure Equipment Directive

EN 285 – Steam sterilizers – Large sterilizers

EN ISO 14971 – Medical devices – Application of risk management to medical devices

EN ISO 17665-1 – Sterilization of healthcare products - Moist heat - Part 1: Requirements for the

development, validation and routine control of a sterilization process for medical devices.

IEC EN 61010-1 – Safety requirements for electrical equipment for measurement, control and laboratory

use – General requirements

IEC EN 61010-2-040 – Safety requirements for electrical equipment for measurement, control and

laboratory use – Part 2-040: Particular requirements for sterilizers and washer disinfectors used to treat

medical materials

IEC EN 60601-1-6 – Medical electrical equipment Part 1: General requirements for basic safety and

essential performance – Collateral standard: Usability.

IEC EN 61326-1 –Electrical equipment for measurement, control and laboratory use - EMC

requirements - Part 1: General requirements

Local market requirements Local regulations on pressure vessels, safety and cycles

Regulations to be followed by autoclave manufacturers


A steam is a pressure chamber used to sterilize equipment and supplies by exposing them to closely

controlled high pressure saturated steam at high temperatures for a predetermined time.

Autoclave – Key components

A sterilizer consists of a

- Steam generator to generate steam for the

jacket and chamber

- Chamber or otherwise called pressure vessel

where sterilization occurs

- Separate jacket that contains steam and

surrounds the chamber which it heats.

- Vacuum pump to generate vacuum in the

chamber

- Control system and user interface

- Electrical control panel

- Piping systems

- Options such as water saving packages


1. Autoclave connected to an external clean steam supply: type “V”

2. Autoclave with integrated electrically heated steam generator: type “E” Steam is produced by the integrated electrically heated steam generator

3. Autoclave connected to an external industrial steam supply: type “I” Steam used is produced by the integrated steam generator heated by the industrial

(indirect) steam

4. Autoclave with an integrated steam generator with mixed heating (both electrical

and connected to an external industrial steam supply: type “E/I”

The steam used is produced either by the steam generator electrically heated or heated

by the industrial steam

5. Autoclave combining both integrated steam generators and external steam

sources: type “E/V”, “I/V

Steam generation options


Standard connections

Electrical, water and steam connections are located on top of Steelco sterilizers.

Electrical supply:

Standard is: 3 x 400V 50 Hz 3 Phase + earth – no neutral. Other voltages on request

Water:

• City water is used for drain cooling system and the vacuum pump.

• Separate water inlets for the steam generator and the vacuum pump -> for “E”, “E/V”, “I”, “E/I”

models.

Compressed air:

Required for pneumatic valves

Drains

Either heat resistant drains to 134º C or cooling option needed to reduce temperature to under 60º C for heat sensitive drains”

Required utilities


Parameters AAMI ST79 EN 285

Evaporation residue ≤ 15 mg/L ≤ 10 mg/L

Silica ≤ 2 mg/L ≤ 1 mg/L

Iron ≤ 0.2 mg/L ≤ 0.2 mg/L

Cadmium ≤ 0.005 mg/L ≤ 0.005 mg/L

Lead ≤ 0.05 mg/L ≤ 0.05 mg/L

Other heavy metals ≤ 0.1 mg/L ≤ 0.1 mg/L

Chloride ≤ 3 mg/L ≤ 2 mg/L

Phosphate ≤ 0.5 mg/L ≤ 0.5 mg/L

Conductivity (at 25°C) ≤ 50 µS/cm ≤ 5 µS/cm

pH 6.5 to 8 5 to 7.5

Appearance Clean, colorless, no sediment Clean, colorless, no sediment

Hardness ≤ 0.1 mmol/L ≤ 0.02 mmol/L

Recommended water quality in USA and Europe


Compatibility with 3 different protective packaging systems

Wrapped instruments

Heat sealing sealed packaging

Container systems

Whichever system is used, sterilization conditions need to be achieved inside the

protective packaging material, with goods being sterile and dry at the end of the

process with the integrity of the protective packaging not compromised


1. 2.

3. 4.

5.

7. 6.

8.

9.

1. START Door closes, seals and

jacket heats chamber

2. AIR PURGING Steam enters

chamber, and air is forced down

and out through drain

3. CONDITIONING Pulsed

positive and negative pressure

with continued load heating and

air evacuation

4. HEAT AND PRESSURE BUILD UP to selected cycle (usually 134ᴼ C or 121ᴼ C temperature)

5. STERILIZATION EXPOSURE at selected cycle (usually 134ᴼ C or 121ᴼ C temperature)

6. EXHAUST Vacuum created in chamber with steam exhausted through drain

7. DRYING under vacuum in chamber for predetermined length of time

8. RETURN TO ATMOSPHERIC PRESSURE

9. LOAD RELEASE Door is opened and goods are released

Temperature

Pressure

Typical cycle on Steelco sterilizer


Standard sterilizer cycle 1 / 4

Legend








• Vacuum pulse air removal

LOAD

AIR

AIR

AIR

AIR

AIR


Steam surrounds load

LOAD


Attraction of steam on load due to condensation

LOAD

STEAM

STEAM

STEAM

STEAM

CONDENSATE


Vacuum pulse removing air, steam and condensate

LOAD

AIR, STEAM & WATER

AIR,

STEAM

& WATER

AIR STEAM & WATER

AIR, STEAM

& WATER


Successful penetration of steam to centre of mass

SATURATED STEAM

SATURATED STEAM

SATURATED STEAM LOAD

SATURATED STEAM

OK


STEAM

STEAM

STEAM

STEAM

LOAD

Insufficient air removal, air leaks or poor steam quality

AIR/GAS POCKET



Wet steam

Wet steam at saturation temperature

contains more than 5% water. Wet steam lowers

the heat transfer efficiency of steam, resulting in

ineffective sterilization with wet packs that can

have associated microbial growth

Wet steam, condensate and subsequent wet

packs is a most common issue for CSSD staff.

It’s possible causes and good practices to avoid

issues are reviewed later in this presentation


Non condensable gases

Gases that cannot be condensed such as air left in chamber

Sources of non condensable gases

1. Inadequate air removal from the sterilization chamber

2. Leaks in door seals, valves or screw fittings,

3. NCGs is the feed water used to generate steam due to: Steris example

• Dissolved air in the water when it is heated.

• Hydrogen carbonate salts (limescale) dissolved in the feed water producing carbon dioxide

(CO2)

Dangers created

1. Insufficient energy delivered to sterilize load as less latent heat energy than steam.

2. Gas pockets insulate surfaces or block lumens preventing steam condensate sterilizing them

Detection

Usually detected by air leak detector in sterilizer and good quality Bowie Dick tests

Non condensable gases (NGS)


Part 6.

Tests and cycles on an autoclave


Autoclaves should be factory programmed with the following safety tests Heating Undertaken in combination with a vacuum test to ensure that correct heating temperature is reached in appropriate time

Vacuum test Used to verify the vacuum integrity of the sterilizer chamber and the effective removal of residual air in the load. The cycle is performed with an empty chamber. Excessive time to create a vacuum is likely to indicate a leaking valve or door gasket

Safety tests 1 / 3


Bowie-Dick Test:

Mandatory daily machine release test to

verify the effectiveness of saturated

steam penetration and air removal.

Cycle parameters are preprogrammed

and undertaken in an empty chamber

with a class II Bowie Dick pack that is

checking mechanical effectiveness of

sterilizer

Safety tests 2 /3


Helix Test: Optional load release test

used to verify the steam penetration and

air removal when processing hollow

instruments.

Some markets incorrectly assume that this

replaces a Bowie Dick test. This is not the

case as standards call for air to be able to

be absorbed from all sides of the test

device. In a helix test steam is drawn in

through a narrow tube opening

Safety tests 3 /3


Type of sterilizer Item Exposure time at

250ºF (121ºC)

Exposure time at

270ºF (132ºC) Drying time

Gravity displacement Wrapped instruments 30 min 15 min 15-30 min

Textile packs 30 min 25 min 15 min

Wrapped utensils 30 min 15 min 15-30 min

Dynamic-air-removal (e.g.,

pre-vacuum)

Wrapped instruments 4 min 20-30 min

Textile packs 4 min 5-20 min

Wrapped utensils 4 min 20 min

Sterilization exposure times and temperatures

Sterilization exposure times and temperatures vary according to:

• Type of sterilizer

• Goods to be sterilized

• National guidelines and practices

132 -134°C is commonly used for standard wrapped instruments in many countries, however

the length of time the sterilization plateau varies between different countries from 3.5, 4, 5, 5.3,

7, 8 and 18 minutes for prion cycles. Steelco sterilizers are programmed with the most

commonly used cycle programs, however programs can be set for different international

market requirements

Example of cycle quoted in USA


Cycle is specifically for thermosensitive items such as plastic and rubber items

Standard 121°C cycle

Sterilization temp: 121°C

Sterilization time: 20 minutes

Drying time: 10 minutes





Cycle is specifically for instruments

Instrument 134°C cycle – EN285 small load





Porous loads, and textile cycle

Cycle is specifically for porous loads, and textiles


Other special cycles available on request

• Optical instruments

• Prion 134°C cycle with 18 min sterilization plateau or according to local requirements

• Silicone implants

• To be agreed with customer after verification of suitability

Other optional cycles available on request


Part 7.

Monitoring sterility of goods


Indicator classes

Class 1: Process indicators

Class 2: Indicators for use in specific tests - (Eg Bowie Dick)

Class 3: Single parameter indicators

Class 4: Multi-parameter indicators

Class 5: Integrating indicators

Class 6: Emulating indicators


106 105 104 103 102 101 100 10-1 10-2 10-3 10-4 10-5 10-6

0 1 2 3 Mins.

No

. o

f M

icro

-org

an

ism

s

Assumed Bioburden of 106 Micro-organisms Reduction of spore survivors

Log reduction example 134°C cycle 1 / 3

Numbers of spores

surviving after 1

minute of exposure


106 105 104 103 102 101 100 10-1 10-2 10-3 10-4 10-5 10-6

0 1 2 3 Mins.

No

. o

f M

icro

-org

an

ism

s

Assumed Bioburden of 106 Micro-organisms

SAL 10-6



Likelihood of 1 spore surviving after 2 minutes is 1 in a million i.e 10-6

Log reduction example 134°C cycle 2 / 3


Minimum of 1

Min. Safety Time

106 105 104 103 102 101 100 10-1 10-2 10-3 10-4 10-5 10-6

0 1 2 3 Mins.

No

. o

f M

icro

-org

an

ism

s

Assumed Bioburden of 10C Micro-organisms

SAL 10-6



Log reduction example

Note: Standard sterilization exposure time on 134oC cycle is 5 minutes on a Steelco sterilizer


A simple visual colour change indication which

only proves that an item has been subject to a

sterilization process

Does not prove if parameters necessary for

sterilization have been achieved

Predominantly used outside of packaging or in

pouches or tabs on containers to show whether

the goods have been in a sterilizer or not

Class 1 indicator


Class 3 indicators (not commonly used – not offered by Steelco)

Prove that one or more parameters of the sterilization

process such as temperature or time were present

Class 4 indicators (commonly used – low cost)

Prove that 2 or more of the parameters of, temperature,

steam and time were present. Calibrated at 3.5mins

Tolerances are: Time +0%, to - 25%

Temperature +0, to -2C

Class 3 and 4 indicators


Class 5 - Integrating Indicators

( not commonly used – not offered by Steelco)

• A Chemical indicator that copies the results of a

biological indicator

• Must react to all critical parameters of process, i.e

time temperature and presence of steam

• Follow the death curve of a given spore

population, e.g. G. Stearothermophilius

Tolerances are:

1. time +0%, - 15%

2. temperature +0°C, -1°C

Class 5 indicators are available but not recommended by

Steelco as they are calibrated to change colour when a

biological indicator changes. Class 6 indicators are

calibrated to change colour at the end of the sterilization

plateau according to the time used by the customer.

Class 6 calibrated to change colour

at end of sterilization

plateau

Class 5 calibrated to change colour at

approximately 1 minute from start of sterilization plateau


Class 6: Emulating indicators

• A Class 6 indicator proves that all parameters of time temperature and

presence of steam were present as per values stated on the indicator e.g. 3.5, 4,

5, 5.3, 7, 8, 12 or 18 mins @ 134°

• Sterilizer Cycle emulatied

• For steam the tolerances are;

Time +0%, - 6%

Temperature +0, -1C


Comparison between Class 4 and 6 indicators

Class 6 indicator

1. Cycle specific calibration

2. 3.5, 4,5, 5, 5.3, 7, 12 and 18 @134C

3. Greater accuracy

Example on 3.5 minute indicator

• 3.5 mins = 210 seconds

• 6% tolerance on 3.5 mins = 12. 6 seconds

• Calibration between 197.4 and 210 seconds

Class 4 indicator

1. Generic calibration of 3.5 minute@ 134 C

2. Cheaper to buy

3. Available as twin strip that can be cut in half

for cost saving

Example on 3.5 minute indicator

• 3.5 mins = 210 seconds

• 25% tolerance on 3.5 mins = 52. 5 seconds

• Calibration between 157.5 and 210 seconds


Biological indicators

• Usually contain 105 or 6 Geobacillus

stearothermophilus

• Some systems have 1-3 hour prediction using

enzymatic correlation whilst other have a 3-5

hour initial positive detection for failed cycle

alert based on microbiology

• Full incubation times used to be 24 hours but

now down to 10-12

• Mostly used in the USA where a requirement

especially when sterilizing orthopaedic sets

• Also available together with a chemical

indicator in a pack

biological

indicator for use with incubator


Part 8.

Avoiding common problems associated with sterilizers


Overview of issues

Steam sterilization is a mature 150 year old technology with standards

relating to performance closely regulated. Sterilizers from reputable

manufacturers are generally hard wearing and reliable with most issues

related to:

• Utilities being outside of specifications

• Incorrect loading

• Inappropriate cycle used for load

• Repairing in the event of a breakdown rather than observing

manufacturer’s service interval recommendations

• Lack of staff training

19th Century sterilizer


Utilities outside of specification

Manufacturers provide detailed utility and water

quality information for their equipment

Problems can arise when

• Use of water or steam outside of specification

• Different water sources are used during the

year ( snow melt water v Summer bore hole)

• Old piping releasing sediment

• Heavy simultaneous use of same utilities by

equipment in hospital

Many problems can be eliminated through

• Regular sampling of water quality

• Optimized pipe runs and regular cleaning of

steam traps

• Ensuring system free from impurities from

utilities or from packaging / goods


Effects of contaminated water

1. Rust from piping

2. Biofilm in level sensor

3. Limescale deposits in sterilizer piping

1

3 2

3


Deposits can be from water or load (detergent, lubricant , rust, etc..) and: • Create hotspots in sterilizers • Act as a insulator reducing heat

transfer. Longer cycles and higher bills

• Decreases drying effectiveness • Contaminate load

Limesacale usually removed with acid/ descaler by dissolving carbonates that hold deposits

Deposits in sterilizer chamber


What are wet packs, how do they occur, and are they important ?

• Wet packs are any part of the load that is not dry after the end of the sterilization cycle

when the chamber door is opened

• Wet packs occur because condensate gets separated from the energy needed to

ensure evaporation

• Energy is needed from the environment to evaporate the condensate

• Packs or devices coming wet out of the sterilizer must be considered as non

sterile as it cannot be guaranteed that saturated steam has been in contact with the

entire surface of the goods according to the sterilization cycle

Avoided by:

• Correct piping, steam traps and functionality of sterilizer

• Uncompromised barrier system

• Correct loading of sterilizer chamber

• Utilities and in particular water and steam supply within specification 24/7

What are wet packs ?


Wet or unsterile goods due to incorrect pouch or wrapped items loading

OK X

1. Air needs to be

removed

2. Saturated steam at

correct temperature

needs to penetrate

packaging material and

be in contact with all

surfaces during sterili-

zation plateau

3. Steam must be

removed with surfaces

and packaging dry

after process.


Wet packs – loading problems

Wrapped items and pouches are densely packed in chamber:

Air may remain trapped in or between loads creating a barrier to saturated steam from being in contact and sterilizing surface.

Loads touching chamber surface

Physical barrier to steam penetration

Instrument containers may be damaged with blocked or closed valves / filters

Pouches items are stacked on each other

Use correct pouch racks and pouches that hold pouchs horizontally upright position allowing

the passage of condensate to sterilize and drying under vacuum after sterilization

Load density

The denser the mass the greater the attraction of condensate onto the cooler surface of the

load. Containers / wraps should not be over packed and kept within load limit. Densest /

heaviest items should be placed on bottom shelf to prevent condensate from pooling and

dripping on items below. As absorbed condensate dries faster than pooled water, some

hospital consider placing a suitable lint free sheet on loading cart shelf under heavy item

Plastic materials

Plastic material have low heat absorption and latent heat retention properties, cooling down

faster making plastic dental trays, etc… more susceptible to poor drying


Wet packs – Equipment problems

Water temperature of the vacuum pump feed:

• Water boils at 39°C at 1 PSI / 0.7 bar vacuum. If water inside the water ring vacuum pump is

not kept below boiling point, vacuum cannot be achieved. Mostly a problem in hot climates

when incoming water temperature is already high and heats up further due to mechanical

friction and heat energy released from the sterilizer

Variable centrally generated steam quality

• Pressure drop during peak demand such as when other departments use simultaneously

Poor system design and or maintenance

• Poor pipe runs, insufficient insulation, steam traps not maintained to service schedule needs

• Wet instruments from washer will remain wet in sterilizer

Chamber drain valve filter

• Needs to be regularly cleaned of any debris that could prevent correct evacuation of steam

from the chamber and lead to rain out


Wet packs - Additional possible solutions

Underlying root wet pack problem should be identified and resolved. A few additional points include: • Extending drying time

• Using tray liners that absorb condensate using instruments’ latent heat

• Changing preconditioning and post conditioning vacuum pulses ( number of pulses,

depth, peaks and holding time) to enable air evacuation (preconditioning) and enhanced drying (post conditioning)

• If incoming water temperature is too hot for vacuum pump, either draw shallower vacuum (lowering boiling point) for longer or consider installing a water chiller to cool feed water. A chiller has the added benefit of enabling the recirculation of the water needed for the vacuum pump rather than sending it to drain after it has been cooled down with tap water, with the additional benefit of approximately 90% water saving being achieved.


END

Documents

Introduction to sterilization...Types of sterilization media High Heat • Dry heat • Moist steam Low Heat • Ethylene Oxide (ETO) • Formaldehyde • Hydrogen peroxide vapour