SDAPharma Symonds Davies Associates AUTOCLAVE CHART CHECKING & TESTS
AUTOCLAVE CHART CHECKING All charts are usually subject to routine checks and reviews against critical parameters, but tendency to focus on the defined limits for the sterilization phase only for temperature, pressure and absence of alarms. However it is essential to check the complete autoclave cycle profile to determine whether it is typical of the Master Process profile.
AUTOCLAVE CHART CHECKING Check time, values and number of negative pulses Atypical traces may indicate leakage, vacuum pump issues
AUTOCLAVE CHART CHECKING Check time, values and number of positive pulses Atypical traces could indicate leakage, issues with steam supply, control sensors, valves etc.
AUTOCLAVE CHART CHECKING Check for extended heating times Could indicate failure to remove air, vacuum issues, leakage, presence of NCGs in steam
AUTOCLAVE CHART CHECKING Check for sterilization temperature, pressure and time. Failure to maintain specified conditions could indicate issues with steam supply, control sensors etc.
AUTOCLAVE CHART CHECKING Check vacuum drying phase for atypical values in temperature, time and depth of vacuum Atypical trace could indicate vacuum pump problems, leakage etc.
SCHEDULE OF PERIODIC TESTS FOR POROUS LOADS HTM2010, EN285 Daily/Weekly: Bowie-Dick test for steam penetration, Vacuum leak test, Air detector function test, Automatic Control Test Quarterly: Verification of calibration probes, Thermometric test for a small load. Six Monthly: Thermometric tests for full loads, Steam non-condensable gas test, Steam superheat test, Steam Dryness test The schedule is more extensive than those listed above. The daily and weekly tests are extremely valuable together with standard chart checking to detect faults and issues which may otherwise go undetected until full thermometric testing.
BOWIE DICK STEAM PENETRATION TEST To steam sterilize items, steam must come into direct contact with every surface of each item to destroy any microbes that may be present. Getting steam to penetrate though packaging, pouches, tubing etc can be difficult as any air present can become trapped within the load and act as an insulating barrier. The Bowie-Dick test consists of a test pack which has a chemical indicator sheet located in the centre. Following a Bowie-Dick sterilization cycle, colour changes on the sheet indicate whether satisfactory air and other non-condensable gases have been removed and steam has penetrated through the test pack. The classic test consisted of freshly laundered towels, but many commercially prepared kits are now available e.g. Steris, 3M etc. The tests may provide important information regarding the ongoing performance of the sterilizer.
BOWIE DICK STEAM PENETRATION TEST Unused sheet
BOWIE DICK STEAM PENETRATION TEST PASS: Cycle Satisfactory Uniform colour change from yellow to blue/purple. Consistently achieving this result demonstrates satisfactory ongoing performance. Note it is important to store and handle sheets correctly to avoid false results.
BOWIE DICK STEAM PENETRATION TEST FAIL: Possible Cause Inadequate air removal 1. Faulty vacuum pump incapable of drawing a deep enough vacuum. 2. The water temperature to the vacuum pump is too high preventing a good vacuum in the chamber. 3. A faulty pressure switch/sensor giving an incorrect reading.
BOWIE DICK STEAM PENETRATION TEST FAIL: Possible Cause Leak 1. A leak in the chamber door seal owing to wear or damage. 2. A leak in the sensor ports attached to the chamber. 3. A high pressure leak from a pneumatic valve into the steam supply to the chamber. 4. A venturi leak through pipe-work where steam is passing at high velocity.
STEAM QUALITY TESTS EN285 These should be undertaken on a six monthly basis or whenever there is an interruption in the steam supply to assure steam quality. To be most effective, the Steam supplied to autoclaves must be dry saturated (composed of water vapour in a state of equilibrium between condensation and evaporation). The release of latent heat as the steam condenses to moisture on the item to be sterilized causes the coagulation of cellular proteins causing the destruction of micro-organisms. Routine Bowie-Dick testing may indicate issues which would otherwise not be detected until the periodic thermometric and biological testing and calibration checks are performed.
STEAM QUALITY TESTS EN285 Test for Non-Condensable Gas This includes air and other gases which will not condense to liquid state and release latent heat under sterilization conditions. During sterilization the flow of steam is always towards a component. As any gases are liberated at the point of condensation, NCGs will be forced by the flow of steam towards the product. If the product is hollow or porous, the air will be forced towards the centre of the product. Air is approximately 12,000 times more resistant to heat transfer than copper. Whether present as a film or pocket, it may prevent direct steam contact or insulate the component. Such conditions are identical to inadequate air removal. A sample is taken from the steam supply to the autoclave and condensed. The level of NCG is determined by comparing the amount of water displaced in a burette against the steam condensed. The maximum permitted level is 3.5% gas/condensate.
BOWIE DICK TEST STEAM QUALITY FAIL: Possible Cause Non Condensable Gas (NCG) in the steam supply 1. Boiler Feed Water Treatment NCGs are gasses found in steam which do not condense when the steam turns to water. Source is usually at the point of generation or in the distribution system 2. Issues with the Still feed water 3. Leak
STEAM QUALITY TESTS EN285 Superheat Test: Excessive amounts of superheat could mean that there is no moisture available to effectively sterilize, leading to dry heat conditions. i.e. steam will not condense and provide moisture until the steam temperature has reduced to the saturation temperature. It therefore acts as hot air or dry heat. The test requires the fitting of an expansion tube onto the pitot tube used in the Dryness Test. A temperature sensor measures the superheat if any as the steam expands to atmospheric pressure. Degrees of superheat measures in free steam at atmospheric pressure shall not exceed 25.
BOWIE DICK TEST STEAM QUALITY FAIL: Possible Cause Superheated Steam 1. Steam supply pressure is too high. 2. Chamber jacket is being operated at a temperature higher than the chamber during sterilization. 3. Badly engineered steam supply pipe-work resulting in high steam velocities.
STEAM QUALITY TESTS EN285 Dryness Test Excess condensate in the steam can cause can cause an initially dry load to be taken out wet. This can make the load much more vulnerable to recontamination. In addition water can act as an insulator and prevent good heat transfer. The dryness value is determined on a sample of steam which passes through a pitot tube located in the steam supply and into cold water in a flask. The initial and final mass and temperature of the water in the flask is used to derive the value. The value should not be less than 0.90 or 0.95 when sterilizing metal loads
BOWIE DICK TEST STEAM QUALITY FAIL: Possible Cause Poor Quality Wet Steam 1. Inadequate baffling in boilers 2. Undersized boiler for application 3. Poorly lagged steam pipe-work 4. No condensate trap near sterilizer 5. Cold chamber jacket due to fault 6. Jacket operating at reduced temperature 7. Test has been carried out in a cold chamber
VACUUM LEAK TEST (AKA AIR LEAKAGE TEST) To ensure high standards of performqnce for porous load autoclaves, leakage into the chamber while it is under vacuum, must be controlled. Leakage before and during sterilization will affect sterilization efficacy. Leakage following sterilization may contaminate the load. To assess and monitor leakage EN285 recommends a minimum vacuum of 70mbar absolute is created within the chamber. When the desired vacuum value is attained, the main control values to the chamber are closed and the vacuum pump stops. After a 5 minute stabilization period, the decay in the chamber vacuum is monitored for the following ten minute period. The maximum permitted decay is 1.3mbar per minute over 10 minutes.
AIR DETECTOR TEST The Air Detector is a device located within the region of the chamber drain for demonstrating that air in the chamber environment and throughout the load under worst case conditions has been reduced to an acceptable level on each and every cycle. It measures the presence of the last remaining air in the load. There are two types: Temperature Sensing and Pressure Sensing. The devices are set up and calibrated during qualification and are very sensitive to air within the load. They are far superior to the drain probe in detecting the presence of air (from leaks, steam supply or the load itself). A review of log books may reveal periodic, infrequent failures.
RECOMMENDED SCHEDULE OF PERIODIC TESTS FOR POROUS LOAD AUTOCLAVES TEST Air Detector Test Air Detector Function Test Leak Rate Test Bowie Dick Test Pack Equilibration Time Vent filter Integrity Test Thermometric Test Thermometric and BI Test FREQUENCY Every Cycle Monthly Daily Weekly 6 months 12 months 6 months 12 months
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