Indicators in Dry Heat Sterilization

Physical indicator: In this process, a temperature record chart is made of each sterilization cycle with dry heat sterilization. This chart forms the batch documentation and is compared against master temperature records. The temperature should be taken as the coolest part of the loaded sterilizer, further thermocouple is used for heat distribution and penetration within the sterilizer.

Chemical indicator: It is based on the ability of heat to alter the chemical or physical characteristics of a variety of chemical substances. Chemical indicators generally undergo melting or color change. This change should take place only when the satisfactory condition for sterilization prevails.

Biological indicator: The biological indicators are the standardized bacterial spore preparations which are usually in the form of suspension in water or culture medium or of spore dried on paper or plastic carriers, they are placed in a sterilizer (Table). Example: Clostridium species is generally used for dry heat sterilization indicators.

Table: Indicators in dry heat sterilization

Indicators	Sterilization Method	Principle	Device	Parameter monitored
Physical	Dry heat	Temperature recording charts	Temperature recording charts	Temperature
Chemical	Dry heat	Temperature-sensitive colored solution	Browne’s tube	Temperature, Time
		Temperature sensitive chemical	A temperature-sensitive white wax concealing a black marked	Temperature
Biological	Dry heat	Temperature sensitive microbes	Bacillus subtilis	D-value