Items that can be sterilized with dry heat:
(1) metal, including surgical instruments
(2) heat stable glass (Pyrex brand, others)
(3) ceramics
(4) certain fabrics, including surgical dressings or drapes
Items that may melt at high temperature or become unusable should not undergo dry heat sterilization. Sharp instruments or needles may become dull if heated > 160°C.
Items need to be decontaminated and cleaned prior to heating. Complex instruments do not need to be taken apart or opened since the heat will reach all areas.
Containment of items so they can be handled once sterilized:
(1) wrapped in 2 layers of an impermeable material (foil or muslin)
(2) in a metal container with a closed lid
|
Temperature in °C
|
Equivalent in °F
|
Duration Once at Temperature
|
|
140
|
284
|
3 hours
|
|
150
|
302
|
2.5 hours
|
|
160
|
320
|
2 hours
|
|
170
|
338
|
1 hour
|
This is linear over the range of 140-160°C, but then the negative slope becomes steeper allowing for shorter heating intervals. If a duration of 1.5 hours would be used at 170°C, then it would be linear over the entire range:
duration at temperature in hours =
= (-0.05 * (temperature in °C)) + 10
One cause for failure is that a heavily wrapped item may not reach full temperature until later in the cycle. Normally this is not a problem considering the long heating periods. The best solution is to have a temperature probe wrapped to a similar extent and to time the heating cycle only when the probe reaches the target temperature.
The total cycle time is at least 2 times the time once at temperature, to allow for heating and cooling intervals. The oven door should not be opened once the baking period has started. If it is opened then the duration of heating needs to be lengthened to compensate for any drop in temperature.
