Sound level meter
6.51 An integrating-averaging sound level meter is required for the sound pressure test. It should comply with Type 2 of BS EN 60804. Ten microphones are required for a single sterilizer.
Air flow metering device
6.52 A metering device (such as a needle valve) is required to admit air into the sterilizer chamber for the air detector tests, and vacuum and pressure leak tests. The device should be capable of controlling the flow of air into an evacuated chamber. It should be adjustable and have a range which
includes a flow of 0-5 ml min-1 per litre volume of the sterilizer chamber. The error in repeatability between 10% and 90% of the setting range should not exceed ± 5%. The device is connected to the chamber by a valved port provided by the sterilizer manufacturer.
Balance
6.53 A laboratory balance is required for steam dryness tests, load dryness tests and coolant quality tests. It should be capable of measuring the mass of loads up to 2 kg to an accuracy of 0.1 g (dryness tests), and up to 100 g to an accuracy of 0.1 mg (coolant quality test).
Gas monitoring instrument
6.54 A gas monitoring instrument, such as an infrared spectrophotometer, is required for tests on LTSF and EO sterilizers.
6.57 The scale ranges should include the appropriate short-term exposure limits specified in Table 1, and extend to at least ten times the exposure limit. The two functions may be combined in one instrument.
Aerosol generator
6.58 An aerosol generator is required for tests on dry-heat sterilizers.
6.59 The device should be capable of generating a polydisperse aerosol with particles having the size distribution shown in Table 7.
Table 7: Particle size distribution for aerosol generator Particle size [µm] Fraction by mass[%] <0.5 >20 <0.7 >50 <1.0 >75 Source: BS 5295: Part 1 Photometer
6.60 A photometer is required for tests on dry-heat sterilizers.
6.61 The device should be suitable for estimation or comparison of mass
concentration of airborne particles as defined in Table 7. It should have an accuracy of better than ±5% over the range of a five-expandable, six-decade resolution (that is, 0.01% to 100% of the test cloud) as specified in Appendix C of BS 5295: Part 1.
6.62 The photometer should have a minimum threshold sensitivity of 0.0001µg l-I and should be capable of measuring aerosol concentration in the range 80- 120µg I-1
6.63 The sample flow rate should be 0.40 ± 0.05Is-1 and sampling should be via a suitable probe device.
7. Testing methods
Introduction
7.1 This chapter discusses general principles and methods that are used in the thermometric and microbiological tests described in this SHTM.
Terminology
7.2 For the purposes of this SHTM the following definitions have been adopted.
Cycle variables
7.3 The cycle variables are the physical properties, such as time, temperature, pressure, humidity and sterilant gas concentration, that influence the efficacy of the sterilization process. Most of the tests described in this SHTM require the values of cycle variables to be determined experimentally and then compared with standard values.
7.4 An indicated value is that shown by a dial or other visual display fitted permanently to the sterilizer.
7.5 A recorded value is that shown on the output of a recording instrument fitted permanently to the sterilizer.
7.6 A measured value is that shown on a test instrument, such as a
thermometric recorder or a test pressure gauge, attached to the sterilizer for test purposes.
7.7 A noted value is that written down by the operator, usually as the result of observing an indicated, recorded or measured value.
Sterilization conditions
7.8 Most operating cycles have a stage in which the load is exposed to the sterilization (or disinfection) conditions for a specified length of time. This period is known as the holding time.
7.9 The sterilization conditions are the ranges of the cycle variables which may prevail throughout the chamber and load during the holding time.
7.11 Together, the equilibration time and the holding time constitute the plateau period. While the plateau period can always be determined from the recorded chamber temperature, the equilibration and holding times cannot be distinguished unless the temperature in the part of the load that is slowest to reach the sterilization temperature is also being recorded or measured.
7.12 Certain LTSF sterilizers may achieve sterilization by exposing the load to a series of pulses of formaldehyde rather than a single holding time.
7.13 For EO sterilizers the plateau period is equivalent to the gas exposure time. The holding time cannot be determined by thermometry and is therefore of no practical interest.
7.14 For steam and dry-heat sterilizers, the sterilization conditions are specified by a sterilization temperature band, defined by a minimum acceptable temperature, known as the sterilization temperature, and a maximum allowable temperature. A sterilization temperature band can also be quoted for LTSF and EO sterilizers, but since these processes depend primarily upon chemical action such a band is not a complete specification of the sterilization conditions. Bands for the different types of sterilizer are listed in Table 8.
Table 8: Sterlization temperature bands
High-temperature steam Dry heat LTS LTSF Ethylene oxide Sterilization temperature (°C)a 115 121 126 134 160 170 180 71b 71 30-56 Maximum allowable temperature (°C) 118 124 129 137c 170 180 190 80 80 d Minimum holding time (min) 30 15 10 3 120 60 30 10 180e f
Notes:
a. The temperature setting on the automatic controller will not generally be the sterilization temperature, but a higher temperature within the sterilization temperature band.
b. Disinfection temperature. c. British Standards permit 138°C.
d. For EO, the maximum allowable temperature will normally be 4°C above the sterilization temperature.
e. For LTSF, the sterilization conditions may specify either a continuous holding time or the number of pulses for formaldehyde required to achieve sterilization.
f. For EO, the “gas exposure time” is determined for each sterilizer by microbiological methods during commissioning but is typically 2-7 hours depending upon sterilization temperature and gas concentration.