General Introduction Introduction to sterilization

Transcription

1 General Introduction Introduction to sterilization

2 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

3 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 Linen only Pictures courtesy of KLS martin

4 Baskets in standard containers Pictures courtesy of KLS Martin

5 Part 1. Sterilization - just 1 step in reprocessing

6 Sterilization - just 1 step in instrument reprocessing Every chain is only as strong as its weakest link

7 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; 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 g) storage.

8 Part 2. What is sterilization?

9 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.

10 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.

11 Measuring sterilization effectiveness 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 6 log reduction from 1,000,000 to 1 spore

12 No. of Micro-organisms Log reduction example Assumed Bioburden of 10 6 Micro-organisms Mins. SAL 10-6 Reduction of spore survivors Likelihood of 1 spore surviving Minimum of 1 Min. Safety Time

13 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

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

15 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) blade tip 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) Note: Steelco offers a range of stereo viewers to aid inspection Magnified box instrument joint

16 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

17 Dealing with prions 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 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 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 mg/l (Summary from Mutala and Weber )

18 Cumulative log reduction Keep instruments moist Need for effective processes at each stage to achieve acceptable overall log reduction Effective manual leaning (when recommended) Effective automated cleaning Important not to add contamination during packing in clean area Need for appropriate sterile barrier packaging Effective sterilization

19 Part 3. Why steam is the most widely used sterilant

20 Types of sterilization media Low Heat High Heat Ethylene Oxide (ETO) Formaldehyde Hydrogen peroxide vapour (VHP) Gas plasma Dry heat Moist steam 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

21 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

22 Part 4. Critical factors that affect sterilization efficacy

23 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.

24 Steam quality The quality of steam has a direct impact on it s ability to inactivate by denaturing proteins Saturated steam and pressure 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

25 Time and temperature Sterilization time using saturated steam 643 hours at 63 C Saturated steam contains the maximum amount of water without liquid condensate 321 hours at 80 C 80 hours at 100 C 12 mins at 121 C 0.13 mins at 140 C 0.9 mins at 132 C

26 Part 5. How steam sterilizers work

27 Regulations to be followed by autoclave manufacturers 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 Medical devices Application of risk management to medical devices EN ISO 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 Safety requirements for electrical equipment for measurement, control and laboratory use General requirements IEC EN 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 Medical electrical equipment Part 1: General requirements for basic safety and essential performance Collateral standard: Usability. IEC EN 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

28 Autoclave Key components 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. 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

29 Steam generation options 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

30 Required utilities 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

31 Recommended water quality in USA and Europe 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 mg/l 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

32 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

33 Typical cycle on Steelco sterilizer 1. START Door closes, seals and jacket heats chamber 2. AIR PURGING Steam enters chamber, and air is forced down and out through drain Temperature Pressure CONDITIONING Pulsed positive and negative pressure with continued load heating and air evacuation 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

34 Standard sterilizer cycle 1 / 4 Legend

35 Standard sterilizer cycle 2 / 4

36 Standard sterilizer cycle 3 / 4

37 Standard sterilizer cycle 4 / 4

38 Vacuum pulse air removal AIR LOAD AIR AIR AIR AIR

39 Steam surrounds load LOAD

40 Attraction of steam on load due to condensation STEAM STEAM LOAD CONDENSATE STEAM STEAM

41 Vacuum pulse removing air, steam and condensate AIR, STEAM & WATER AIR, STEAM & WATER AIR, STEAM & WATER LOAD AIR STEAM & WATER

42 Successful penetration of steam to centre of mass SATURATED STEAM OK LOAD SATURATED STEAM SATURATED STEAM SATURATED STEAM

43 Insufficient air removal, air leaks or poor steam quality AIR/GAS POCKET STEAM LOAD STEAM STEAM STEAM

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45 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

46 Non condensable gases (NGS) 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

47 Part 6. Tests and cycles on an autoclave

48 Safety tests 1 / 3 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

49 Safety tests 2 /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

50 Safety tests 3 /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

51 Sterilization exposure times and temperatures Sterilization exposure times and temperatures vary according to: Type of sterilizer Goods to be sterilized National guidelines and practices 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 Type of sterilizer Item Exposure time at 250ºF (121ºC) Exposure time at 270ºF (132ºC) Drying time Gravity displacement Wrapped instruments 30 min 15 min min Dynamic-air-removal (e.g., pre-vacuum) Textile packs 30 min 25 min 15 min Wrapped utensils 30 min 15 min min Wrapped instruments 4 min min Textile packs 4 min 5-20 min Wrapped utensils 4 min 20 min

52 Standard 121 C cycle Cycle is specifically for thermosensitive items such as plastic and rubber items Sterilization temp: 121 C Sterilization time: 20 minutes Drying time: 10 minutes

53 Instrument 134 C cycle EN285 small load Cycle is specifically for instruments Sterilization temp: 134 C Sterilization time: 5 minutes Drying time: 10 minutes

54 Porous loads, and textile cycle Cycle is specifically for porous loads, and textiles Sterilization temp: 134 C Sterilization time: 5 minutes Drying time: 10 minutes

55 Other optional cycles available on request 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

56 Part 7. Monitoring sterility of goods

57 Indicator classes Class 1: Class 2: Class 3: Class 4: Class 5: Class 6: Process indicators Indicators for use in specific tests - (Eg Bowie Dick) Single parameter indicators Multi-parameter indicators Integrating indicators Emulating indicators

58 No. of Micro-organisms Log reduction example 134 C cycle 1 / Assumed Bioburden of 10 6 Micro-organisms Numbers of spores surviving after 1 minute of exposure Mins. Reduction of spore survivors

59 No. of Micro-organisms Log reduction example 134 C cycle 2 / Assumed Bioburden of 10 6 Micro-organisms Mins. 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

60 No. of Micro-organisms Log reduction example Assumed Bioburden of 10 C Micro-organisms Mins. Note: Standard sterilization exposure time on 134 oc cycle is 5 minutes on a Steelco sterilizer SAL 10-6 Minimum of 1 Min. Safety Time Reduction of spore survivors Likelihood of 1 spore surviving

61 Class 1 indicator 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

62 Class 3 and 4 indicators 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

63 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 calibrated to change colour at approximately 1 minute from start of sterilization plateau Class 6 calibrated to change colour at end of sterilization plateau 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.

64 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 Sterilizer Cycle emulatied For steam the tolerances are; Time +0%, - 6% Temperature +0, -1C

65 Comparison between Class 4 and 6 indicators Class 6 indicator Class 4 indicator 1. Cycle specific calibration , 4,5, 5, 5.3, 7, 12 and 3. Greater accuracy 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 6% tolerance on 3.5 mins = seconds Calibration between and 210 seconds Example on 3.5 minute indicator 3.5 mins = 210 seconds 25% tolerance on 3.5 mins = seconds Calibration between and 210 seconds

66 Biological indicators Usually contain 10 5 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 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

67 Part 8. Avoiding common problems associated with sterilizers

68 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

69 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

70 Effects of contaminated water 1. Rust from piping 2. Biofilm in level sensor 3. Limescale deposits in sterilizer piping

71 Deposits in sterilizer chamber 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

72 What are wet packs? 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

73 Wet or unsterile goods due to incorrect pouch or wrapped items loading 1. Air needs to be removed OK 2. Saturated steam at correct temperature needs to penetrate packaging material and be in contact with all surfaces during sterilization plateau 3. Steam must be removed with surfaces and packaging dry after process. X

74 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

75 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

76 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.

77 END