Sterilization Techniques in the Real World

1
Sterilization Techniques in the Real World
ISPE WESTERN ANNUAL CONFERENCE Presented By
Scott Pitzer Application Project Manager STERIS
Life Sciences 8 April 2008
2
Overview

• Principles of Steam Sterilization Review
• Sterilizer Cycles and Applications
• Common Problems and Misconceptions of Steam
  Sterilization

3
Principles of Steam Sterilization

• Steam is the ideal sterilant for items that can
  withstand moisture and high temperatures because
  it is
• nontoxic
• readily available
• fairly easy to control
• latent heat
• ISO 17665
• ISO 11138-BI, 11140-CI
• HTM 2010
• EN 554, 285
• PDA Technical Report No. 1

4
Principles of Steam Sterilization

• Steam is Water in the Vapor State
• Steam Heats by Condensing and Giving Up Energy
• Heating water from ambient (15ºC) to boiling
  (100ºC) requires 85 kcal/kg
• To convert liquid to vapor at 100ºC requires 539
  kcal/kg or 6.3 x more energy
• By-product is Condensation
• Remains on product
• Rolls off
• Three factors are critical to assure successful
  steam sterilization
• Time
• Temperature
• Moisture

5
Principles of Steam Sterilization

• TIME
• All organisms do not die at the same time.

6
Principles of Steam Sterilization

• Temperature
• Increasing temperature dramatically reduces the
  time needed to achieve sterilization.

( .13 Minutes )
( 0.9 Minutes )
12 Minutes
80 Hours
321 Hours
643 Hours
(Time to Achieve Equivalent Microbial Lethality
at Different Exposure TemperaturesPopulation
106, D value 2 minutes Geobacillus
Stearothermophilus)

7
Principles of Steam Sterilization

• Moisture
• Steam needs to be saturated for most effective
  moisture penetration.
• Steam denatures or coagulates proteins.
• Dry heat is an oxidation process with different
  kinetics - it requires much higher temperatures
  and longer exposure times
• Geobacillus stearothermophilus spores -killed in
  12-15 minutes at 121C (250 F) when saturated
  steam is used
• More than 6 hours are required to dry heat at
  121C.

8
The Steam Sterilization Cycle
9
The Steam Sterilization Cycle

• The Steam Sterilization Cycle
• A steam sterilization cycle consists of three
  primary phases
• Heating (pre-conditioning) phase
• Sterilization (exposure) phase
• Cool-down (post conditioning) phase

10
The Steam Sterilization Cycle

• Heating (pre-conditioning) phase -
• Steam enters the sterilizer chamber and air is
  removed by either
• gravity displacement
• mechanically (prevacuum)

11
The Steam Sterilization Cycle

• Sterilization (exposure) phase -
• Load is exposed to steam at a set temperature
  for a set time.
• (Usually measured and controlled by a
  temperature sensor in the drain line or product)
  

12
The Steam Sterilization Cycle

• Cool-down (post-conditioning) phase -
• Sterilizer chamber is exhausted to atmospheric
  pressure followed by circulating air through the
  chamber or by drawing vacuum. Jacket heat may
  or may not be maintained during the drying
  phase.

13
The Steam Sterilization Cycle
Post-Conditioning
Pre-Conditioning
VACUUM DRYING
Temperature Pressure Rated pressure
PULSED AIR REMOVAL
Pre-Cycle
FINN-AQUA LEAK RATE TEST
Exposure
EXPOSURE
PULSED DRYING
Temperature
Pressure
Rated pressure
Temperature Pressure Rated pressure
Temperature Pressure
FORCED AIR REMOVAL
Pressure
FAST AND SLOW EXHAUST
Temperature in slow exhaust Pressure in slow
exhaust Pressure in fast exhaust
Temperature
Pressure
14
Common Steam Sterilizer Cycles

• Gravity
• Pre-Vacuum Cycle
• Decontamination Cycle
• Air-over Pressure Cooling (jacket, direct spray)
• Low Temperature (Isothermal) Cycle
• Steam-Air Mixture
• Hot Water Sterilization
• Cycles have air-overpressure during cooling
  phase.
• Cycle have air-overpressure during
  sterilization and cooling phases

15
Basic Gravity Cycle
16
Basic Gravity Cycle
Basic Gravity Cycle

• Applications
• Empty glassware
• Instruments
• Open pans, vats, carboys

17
Basic Liquid Cycle(Modified gravity cycle)

• Generally used to process
• Media/Liquids in open containers
• Water
• TSB
• TSA
• Filled bottles / tubes with loose caps
• Generally at 121oC

18
Types of Gravity Cycles

• Open Drain, Pressurize with Steam
• Forced Air
• Open Drain and control steam flow to maintain 0
  PSIG
• Timed, 0-99 minutes

19
Basic Gravity CyclePre-conditioning and Exposure

• Two Methods of Controlling the Cycle
• Control by Temperature Probe in Drain
• Timed
• Control using Probe in Product
• Fo

20
Basic Gravity CyclePre-conditioning and Exposure

• May use Fo load probe in liquid loads if it is
  available in the sterilizer
• Advantages
• produces desired lethality
• minimal effect on product
• optimizes the exposure period
• Can use time at temperature if probes are not
  available (overkill method)

21
What is F0
Fo as a Function of TemperatureLethality Curve
F0 Value
1.545
123 ?C
122 ?C
1.227
121.1 ?C
1.00
.50
118.1 ?C
.245
115 ?C
110 ?C
.008
Reference Temperature 121.1?C Z - Value 10
?C
22
Gravity CyclePost - Conditioning

• Liquid Cycles are returned to atmospheric
  pressure slowly to
• Prevent boil-over
• Prevent liquid loss
• Rate of slow exhaust depends on
• Volume of liquid per flask / tube
• Total load capacity
• If there is a jacket cooling process built into
  the sterilizer

23
Prevac or Pulsing Vac Cycles
24
Prevac or Pulsing Vac Cycles

• Generally used to process dry goods
• Articles in open trays
• Porous goods such as textiles
• Open, unfilled glassware/plastic bottles
• Rubber stoppers
• Filter cartridges
• Disc filters

25
Prevac Cycle Loads

• Metal articles
• Porous goods (textiles)
• Glassware (open)
• Glassware in pouches
• Plastics (open)
• Plastics in pouches
• Rubber stoppers
• Filter cartridges
• Disk filters

26
Prevac CyclePre-conditioning

• Number and depth of vacuums during
  pre-conditioning can be user selectable
• Based on degree of difficulty to penetrate
  product with steam
• Tygon tubing may take several pulses/vacs to
  penetrate to center of tube
• Long lengths may require deeper vacuum
• Large metal items may require several pulses to
  heat

27
Prevac Cycles Product Constraints

• Ability of the product to withstand
• Vacuums
• Pressure / vacuum rates
• Peel pouches may burst
• Covers may be blown off of covered pipe ends
• May need to control rates if available on
  sterilizer

28
Prevac Cycle

• Exposure Phase
• Timed
• Based on drain line temperatures
• Generally at 121oC but could be at 132oC
• Overkill method employed

29
Post-conditioning phaseSingle deep vacuum, hold

• Used to dry the load
• Basic cycle draws a single deep vacuum and holds
• Hold time varies
• May be 20-45 minutes or longer
• Time depends on
• Material that comprises load
• Packaging
• Level of dryness required

Prevac Cycle
30
Post-conditioningPulsing Vac Cycle

• Pulls vacuum with alternating pressurization with
  air
• Used for peel pouched items, items with low
  specific heat (rubber goods)
• May be unheated or optional heated (HPPD)

31
Steam Sterilizer Cycles
Post-Conditioning
VACUUM DRYING
Pre-Conditioning
Temperature Pressure Rated pressure
PULSED AIR REMOVAL
Pre-Cycle
Exposure
Wrapped Goods
LEAK RATE TEST
EXPOSURE
PULSED DRYING
Temperature
Pressure
Rated pressure
Temperature Pressure Rated pressure
Wrapped Goods Tubing
Temperature Pressure
FORCED AIR REMOVAL
Pressure
Porous Goods (Stoppers)
Time/Temp Fo
FAST AND SLOW EXHAUST
Temperature in slow exhaust Pressure in slow
exhaust Pressure in fast exhaust
Temperature
Pressure
Vented liquids
Metal, Vented Liquids
Gravity and Pre-vacuum
32
Decontamination Cycle
33
Effluent Decontamination Cycle

• Sterilizes effluents from the unit, prior to
  discharge
• Used with dry or liquid loads
• Recommend a Bioseal on pass through sterilizers

34
STANDARD STEAM FLOW
Effluent Decontamination Cycle
DECONTAMINATION CYCLE (EFFLUENT DECONTAMINATION
CYCLE)
35
Air-Over Pressure Cooling
36
Typical Products to be Sterilized with Air-Over
Pressure Cooling
Steam Sterilization with over-pressurized air
duringthe cooling phase

• Liquid loss is prevented for
• Vented containers
• Media or liquid in open containers
• Bottles
• Support pressure maintains container integrity
  for
• Non-vented glass containers
• Ampoules
• Capped vials
• Capped bottles

2.1.5
37
Jacket Cooling

• Steam exhausted from jacket jacket filled with
  water
• Chamber pressurized with AIR
• Used with liquid loads
• Sealed glass or open containers
• Effective way to reduce heat in chamber
• Allows product to be cooled more rapidly

Air-Over Pressure Cooling
38
Post-Conditioning Phases

• Indirect (or forced) jacket cooling(Process C)
• Vented or non-vented containers
• Forced jacket cooling by circulation fan(s)
• (Process CF)
• Over pressurization of chamber with sterile
  compressed air
• Jacket is cooled with domestic water
• Cooling time and final load temperatureare user
  configurable
• Typical phase time 20-40 min. (CF10-20 min.)
• Indirect (or forced) jacket cooling followed
  byvacuum drying
• For drying of the product
• For testing of ampoules
• Vacuum drying followed by jacket cooling
• Cools the chamber for safe unloading
• Typical phase time 10 minutes

INDIRECT OR FORCED JACKET COOLING
Temperature Pressure
INDIRECT OR FORCED JACKET COOLING WITH VACUUM
DRYING
Temperature Pressure
39
Spray Cooling

• Water sprayed over load to cool
• Most effective way of rapidly cooling
• Product will be wet!

40
Air Over-Pressure Cycles(Terminal Sterilization)

• Steam-Air Mixture
• Over-pressurized Water Spray Process

41
Typical Products to be Sterilized with Air
Over-Pressurization Cycles

• Over-pressurized processes are recommended for
• Glass containers
• Stoppered (uncapped) vials and bottles
• Filled syringes
• Plastic containers
• Ampoules
• Capped or uncapped vials and bottles
• Filled syringes
• IV bags
• Blister packs

• Support pressure throughout thecycle is required
  to
• Maintain the shape of plastic containers
• Minimize the syringe piston movement
• Maintain the stopper placement when uncapped
• Maintain the blister pack seal

42
Steam-Air Mixture
43
Air

• Air is generally a deterrent to sterilization
• Occasionally used to assist in controlling
  pressures
• Sealed items with flexible sides
• Plastic vials/ syringes
• Items that can expand and burst
• IV bags

44
Cycle Definitions

• Process AC
• Steam/air mixture cycle (SAM)
• Fan assembly to mix steam and air
• Overpressure maintain throughout cycle
• Pressure and temperature controlled
• Forced air cooling of product
• Plastic and glass products
• Fast cooling (app. 30 - 60 min.)
• Dry products at the end

Pressure Temperature
45
Pre-Conditioning Phase

• Steam-air mixture heating up
• Primarily for plastic containers
• Chamber pressure controlled over the saturated
  steam pressure using sterile compressed air
• Steam and air is circulated and uniformly mixed
  by the fan(s)
• Increased support pressure maintains the package
  integrity
• Pressure curve is configurable based on product
  temperature
• Heating-up rate is user configurable

STEAM AIR MIXTURE HEATING
46
Post-Conditioning Phase

• Steam-air mixture cooling
• Provides the most efficient cooling phase where
  dry product is required
• Pressure curve configurable based on product
  temperature
• Cool down rate is user configurable

STEAM AIR MIXTURE COOLING
47
Steam Air Mixture Cycle
Steam
Filtered compressed air
Pressure balance
Cooling water
48
Over-Pressurized Water Spray(Hot Water
Sterilization)
49
Over-pressurized Water Spray Process

• RP Process
• Water air mixture cycle
• Recirculating water spray system to heat and cool
  the products
• Pressure and temperature controlled
• Water spray cooling
• Plastic and glass products
• Rapid cooling (app. 15 - 30 min.)
• Wet products at the end

Pressure Temperature
Saturated steam pressure
50
Pre-Conditioning Phase

• Overpressurized water spray heating-up
• Primarily used for high through put of plastic
  and glass containers
• Chamber pressure controlled over the saturated
  steam pressure using sterile compressed air
• Overpressurized water is circulated through a
  spray header and nozzles for uniform product
  contact
• Pressure curve configurable based on product
  temperature
• Heating-up rate is user configurable

OVERPRESSURIZEDWATER SPRAY Heating
51
Post-Conditioning Phase

• Overpressurized water spray cooling
• Provides the most efficient coolingphase where
  the product can remainwet at completion
• Pressure curve configurable based on product
  temperature
• Cooling down rate is user configurable

OVERPRESSURIZEDWATER SPRAY COOLING
52
Over-Pressurized Water Spray Process
Filteredcompressed air
Pressure balance
Coolingwater
Steam
Process water
53
Temperature/Pressure Relationship
CurveOver-pressurized Cycles
Processes AC and RP
120C
100C
30 psig
2 bar
80C
ProductTemperature
ChamberPressure
20 psig
60C
40 C 0 bar (0 psig) 60 C
1.4 bar (20 psig) 80 C 2.1 bar
(30 psig)
1 bar
10 psig
40C
Product Temperature
Chamber Pressure
54
Over-Pressurization Cycles
Application Comparison
Steam-Air Mixture Cycle (Process AC)
Over-Pressurized Water Spray Cycle (Process RP)

• Excellent temperature distribution with small
  containers
• Excellent chamber pressure control
• Dry product at the end of the cycle
• Efficient cooling time
• Typical cycle time 60-90 minutes
• No need for final cooling water analysis (FDA/GMP)

• Excellent temperature distribution with medium
  and large containers
• Good chamber pressure control
• No pure steam required
• Wet product at the end of the cycle
• Extremely efficient cooling time
• Typical cycle time 40-60 minutes
• Process water sterilized duringthe process
• Final cooling water analysis needed (FDA/GMP)

55
QUESTIONS?
56
Common Problems and Misconceptions About Steam
Sterilization
57
Misconception

• Assumption Everything Can Be Sterilized
• Facts
• Closed valves on containers do not permit steam
  penetration. Open all valves
• O-rings and seals retard steam penetration. May
  need to remove o-rings or extend processing times
• Upright, empty containers are difficult to remove
  air from with a gravity cycle

58
Test Tubes in Rigid Container

• Fact Solid bottom containers retard steam
  penetration
• Bottom set of tubes in container
• Top set of tubes above container

59
Effects of Rigid Bottom Container
Temperature F
Time (Minutes)
60
Misconception

• Assumption Exposure Time for a Liquid Cycle
  Means That the Product is at Temperature for that
  Period
• Fact Exposure time must account for product
  come-up and desired time at temperature

61
Come-up Rates for Two Different Flask Sizes
62
Common Problems
Steam Quality (HTM 2010) gt Dryness Value gt
Non-condensable gases gt Superheated Steam
63
Common Problems

• Steam Quality Issues
• Dryness Value
• The amount of moisture present in steam is
  measured by the dryness fraction, which is
  directly proportional to the amount of latent
  heat present.
• The dryness fraction describes how dry steam is
  with a value of 1 representing steam that is 100
  dry and free of entrained moisture.
• Steam with a dryness fraction of 0.99 consists of
  99 steam and 1 water.
• Steam that has a dryness fraction of 0.99 we will
  find that it possesses 99 of the full quotient
  of latent heat.  
• Similarly, steam with a dryness fraction of 0.95
  consists of 95 steam and 5 water.

64
Common Problems

• Steam Quality Issues
• Wet Steam
• Wet steam is undesirable as it has less energy
  than dry steam
• Wet steam can cause wet loads
• If metal components are present in the load, wet
  pack problems could be experienced with dryness
  values below 0.95

STERILIZER CHAMBER
PACK
STERILIZER DRAIN
65
Common Problems
Steam Quality Issues Dryness Value The packaging
used for sterile products prevents
re-contamination when dry, but its bacterial
retentive properties will be adversely affected
by moisture. Wet loads can be considered to be
non-sterile.  
Common Problems
66
Common Problems

• Steam Quality Issues
• Causes of Wet Steam
•  
• Wet steam may be caused by excessive pressure
  drops on the boiler due to high demands.
• As the pressure drops, the size of steam bubbles
  increase in turn increasing the volume of water
  in the boiler and causing it to be closer to the
  steam outlet.
• The increased size of the steam bubbles results
  in a more aggressive boiling action, which causes
  more/larger droplets of water to leave the water
  surface and enter the steam space and thus be
  carried over into the steam.
• Steam at a low pressure occupies more space than
  steam at a high pressure and a further affect of
  a pressure reduction is to increase the velocity
  of the steam leaving the boiler.
•  

67
Common Problems

• Steam Quality Issues
• Causes of Wet Steam
• This can reach such a velocity that it will take
  some of the boiler water with the steam.
• Certain contaminants in the boiler water can
  cause a froth to form on the water surface, again
  allowing moisture to enter the steam supply.
• Once in the distribution system, the quality of
  steam is likely to deteriorate as the result of
  heat losses causing further condensation.

68
Common Problems

• Steam Quality Issues
• Solving Wet Steam Issues
• To minimize deterioration of steam quality, the
  steam distribution system should be well
  insulated and have a well designed and installed
  condensate removal system (steam traps and
  separators).
• Piping should always have a slope towards steam
  traps.
• Sagging steam piping can allow pockets of water
  to accumulate
• Large water pockets can occlude the steam pipe,
  causing the increased steam velocity to carry
  them to the points of use in discrete slugs. 
•  

69
Common Problems

• Steam Quality Issues
• Non-condensable gases
• May cause failures with chemical indicators and
  air detectors.
• The effect of such gases being present in the
  steam supply to a sterilizer can be the same as
  inadequate air removal.
• The Bowie Dick Test may fail if approximately
  6.5 of non-condensable gases are present in the
  steam supply.
• Instead of components being heated by steam
  condensing on them, they are heated by a mixture
  of steam and other gases.
• The presence of moisture is essential to the
  sterilization process by allowing the walls of
  cells to coagulate. Non-condensable gases
  interfere with moisture.

70
Common Problems

• Steam Quality Issues
• Superheated Steam
• Superheated steam is steam at a temperature above
  its boiling point for its pressure.
• Superheated steam is a clear colorless gas that
  will not condense until its temperature drops to
  its boiling point.
• Until condensation occurs the moisture necessary
  for sterilization cannot be produced and the
  presence of moisture is essential to the
  sterilization process by allowing the walls of
  cells to coagulate.
• Superheated steam acts as hot air and requires
  sustained high temperatures and long hold times
  before sterilization can occur.
• Superheated steam can be produced
• as the result of excessive pressure drops.

71
Common Problems

• Steam Quality Issues
• Superheated Steam
• If we reduce steam from a high to a low
  pressure its energy level will remain the same.
• This high energy level will initially
  evaporate any moisture present in the steam.
• Any additional energy will then result in a
  temperature increase in the steam and the
  superheat phenomena will become evident.
• Because the superheat will reduce as heat is
  transferred to the load, this is generally a
  temporary phenomena at the start of the
  sterilizing period.
• Superheated steam has the greatest adverse
  impact where high temperature/short time
  sterilizing cycles are used.
• European sterilization cycles of 134C for 3
  minutes are commonly used in healthcare
  applications.

72
Common Problems

• Steam Quality Issues
• Superheated Steam
• Should the duration of the superheat last the
  full 3 minutes, sterilization would not occur.
• Should the same phenomena be present for 3
  minutes of a 30 minute sterilization period, the
  impact is restricted to the initial 10 of the
  holding period.
• Despite, the impact being duration dependent,
  good practice indicates that superheated steam
  should not be tolerated.
• HTM 2010 and EN 285 indicates that pressure drops
  should not exceed a ratio of 21.
• If the pressure drops occurs sufficiently far
  away from the sterilizer, any superheat generated
  will diminish as it loses energy to the pipe
  walls and any moisture present.

73
Misconception

• Assumption All biological Indicators of the same
  population (ie.106) are killed in the same time
  period
• Fact D-values of biological indicators may vary
  from 1.5 to 2.5 minutes. Choose indicators with
  the same D-value as those in which a load was
  validated.

74
Misconception

• Assumption The attainment of 121.10C is a
  significant requirement to sterilize.
• Fact The objective of steam sterilization is to
  deliver lethality. F0 accumulates at all spore
  killing temperatures although it is slower at
  lower temperatures.

75
Misconception

• Assumption A steady state temperature
  distribution range of /- 0.50C is necessary for
  all loads.
• Fact Desirable for terminal sterilization in
  final containers. Not required for sterilization
  of production equipment. Distributions of 10C to
  20C are acceptable

76
Misconception

• Assumption Fixed load patterns are required for
  proper sterilization
• Fact It is not as much the location of the
  items, but the material makeup, wrapping, mass,
  loading procedures and orientation of the load
  that define difficult-to-sterilize locations

77
Suggested Reading

• AAMI Standards Volume 1.2, Sterilization Part 2
  Sterilization Equipment
• AAMI Standards Volume 1.3 Sterilization, Part 3
  Industrial Process Control
• Moist Heat Sterilization- Myths and Realities,
  Agalloco et. al. PDA Journal of Pharmaceutical
  Technology Vol 52, No. 6 Nov-Dec 1998