Manual of basic techniques for a health laboratory - libdoc.who.int

86 Manual of basic techniques for a health laboratorySterilization by steamUsing an autoclaveClinical samples and other contaminated waste materials are placed in a specialautoclave bag or into a metal or plastic bucket for autoclaving. Use the autoclavesterilizing indicators to control the sterilizing cycle.PrincipleWater is heated in a closed container. This produces saturated steam under pressure,with a temperature of over 100°C. Most types of microorganism, includingall bacteria (but not all viruses) are killed when apparatus is heated for 20 minutesat 120°C in this steam under pressure.Components of an autoclave (Fig. 3.63)1. BoilerA large deep cylinder in which the items to be sterilized are placed.2. BasketA big wire basket that holds the materials to be sterilized.3. Basket supportA support in the bottom of the autoclave that holds the basket abovethe water level.4. Drainage tapA tap fitted at the base of the boiler to drain off excess water.5. LidThe lid covers and seals the boiler and is fitted with a rubber washer.6. Lid clampsThese clamps, together with the rubber washer, seal the lid and preventsteam from escaping.7. Air outlet valveA valve at the top of the boiler or on the lid that is used to let air outwhen the water is first heated.8. Safety valveA valve at the top of the boiler or on the lid that lets steam escape ifthe pressure becomes too high and so prevents an explosion.9. Temperature gauge or pressure gaugeAll gauges indicate the temperature in degrees Celsius (°C); somealso have a second set of figures indicating the pressure.Fig. 3.63 Components of an autoclave1: boiler; 2: basket; 3: basketsupport; 4: drainage tap; 5: lid;6: lid clamps; 7: air outlet valve;8: safety valve; 9: temperaturegauge or pressure gauge.Heating systemThe heating system may be built into the autoclave in the form of:— electric elements— gas burners— a paraffin oil stove.