Page 91 - The Veterinary Laboratory and Field Manual 3rd Edition

60 Willy Schauwers

• Minimum and maximum temperature lim-
its are defined for each laboratory device (2) (1)
with temperature control. See ‘FORM-SOP-
LABORATORY-EQUIP-05–05 Temperature
limits Minimum and Maximum’.
• Each temperature control device being used
in the laboratory is checked on a 6 monthly (3)
basis against a certified thermometer (these
are usually kept at the quality control
department). See ‘FORM-SOP-LABORATORY-
EQUIP-05–04-Thermometer control’ and
‘FORM-SOP-LABORATORY-EQUIP-05–
06-Compare temperature with certified
thermometer’. The ‘correction temperature’
is mentioned on each daily temperature
registration form.
• An annual plan for periodic controls (includ-
ing temperature control) is available in
‘FORM-SOP-LABORATORY-EQUIP-06–04-
Quality assurance annual plan’.
Figure 2.21 Autoclaves can be used to sterilize
equipment for simple surgical procedures as well as
autoclaves
laboratory ware, laboratory waste and some instru-
ments. Photo: Willy Schauwers, Provincial Institute
Autoclaves use pressurized steam to ensure
high temperatures for sterilization. Simple for Hygiene, Antwerp, Belgium.
models are metal (aluminium or stainless steel)
containers in which water can be boiled. They When water boils at sea-level atmospheric
have: pressure (sea-level pressure is 1013.25 mbar,
760.00 mm Hg), the temperature of the boiling
• a high-pressure vessel with lid and gasket water is 100°C. When the pressure is increased
• a pressure gauge (1) on the lid to record the inside the autoclave, water will boil at a higher
pressure inside the vessel temperature. The pressure used for sterilization
• a ‘blow off’ valve (2) to release steam after is usually 15 psi (1.1 bar = 100 kPa = 15 lb/in
2
the desired pressure is reached = 15 psi) and at this pressure water will boil at
• a safety valve (3) (Figure 2.21). 121°C. When this pressure and temperature is
applied for 15–20 min most of all known living
Autoclaves range from small, simple domestic organisms are destroyed.
pressure cookers heated on a stove, to extremely Sterilization of articles inside the autoclave
large computerized models. The form of heat- takes place when steam comes into contact with
ing used can be a simple flame (for example, the surface. This moist heat has better penetra-
gas), electric element or steam supplied from tion than dry heat in an oven and is therefore
an external source through a jacket around the a more efficient sterilizer, particularly for bulky
autoclave chamber. items.

Vet Lab.indb 60 26/03/2019 10:25