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General Introduction
Introduction to sterilization
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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
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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
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Baskets in standard containers
Pictures courtesy of KLS Martin
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Part 1.
Sterilization - just 1 step in reprocessing
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Sterilization - just 1 step in instrument reprocessing
Every chain is only
as strong as its
weakest link
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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
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Part 2.
What is sterilization ?
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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.
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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.
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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
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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
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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
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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)
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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
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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
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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
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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
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Part 3.
Why steam is the most widely used sterilant
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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
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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
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Part 4.
Critical factors that affect sterilization efficacy
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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.
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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
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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
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Part 5.
How steam sterilizers work
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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
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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
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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
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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
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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
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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
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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
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Standard sterilizer cycle 1 / 4
Legend
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Standard sterilizer cycle 2 / 4
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Standard sterilizer cycle 3 / 4
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Standard sterilizer cycle 4 / 4
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• Vacuum pulse air removal
LOAD
AIR
AIR
AIR
AIR
AIR
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Steam surrounds load
LOAD
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Attraction of steam on load due to condensation
LOAD
STEAM
STEAM
STEAM
STEAM
CONDENSATE
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Vacuum pulse removing air, steam and condensate
LOAD
AIR, STEAM & WATER
AIR,
STEAM
& WATER
AIR STEAM & WATER
AIR, STEAM
& WATER
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Successful penetration of steam to centre of mass
SATURATED STEAM
SATURATED STEAM
SATURATED STEAM LOAD
SATURATED STEAM
OK
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STEAM
STEAM
STEAM
STEAM
LOAD
Insufficient air removal, air leaks or poor steam quality
AIR/GAS POCKET
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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
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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)
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Part 6.
Tests and cycles on an autoclave
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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
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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
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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
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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
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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
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Sterilization temp: 134°C
Sterilization time: 5 minutes
Drying time: 10 minutes
Cycle is specifically for instruments
Instrument 134°C cycle – EN285 small load
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Sterilization temp: 134°C
Sterilization time: 5 minutes
Drying time: 10 minutes
Porous loads, and textile cycle
Cycle is specifically for porous loads, and textiles
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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
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Part 7.
Monitoring sterility of goods
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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
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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
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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
Reduction of spore survivors
Likelihood of 1 spore surviving
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
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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
Reduction of spore survivors
Likelihood of 1 spore surviving
Log reduction example
Note: Standard sterilization exposure time on 134oC cycle is 5 minutes on a Steelco sterilizer
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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
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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
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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
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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
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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
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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
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Part 8.
Avoiding common problems associated with sterilizers
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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
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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
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Effects of contaminated water
1. Rust from piping
2. Biofilm in level sensor
3. Limescale deposits in sterilizer piping
1
3 2
3
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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
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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 ?
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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.
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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
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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
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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.
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