Question
Describe the principle and applications of autoclave. Add a note on sterilization controls used
Answer
Principle: an autoclave achieves sterilization by moist heat under pressure — raising pressure above atmospheric raises the boiling point of water correspondingly, so steam under pressure (15 lbs/sq inch) reaches 121°C; held for 15–20 minutes, this combination of high temperature, moisture, and pressure kills all microorganisms, including the most heat-resistant bacterial spores, by denaturing and coagulating their proteins. Air (a poor heat conductor) must be fully evacuated from the chamber for the set temperature to be reliably achieved throughout the load.
Construction/working: a double-walled chamber in which steam is generated (internally or supplied externally) and admitted, displacing air via a discharge valve or vacuum pump; a pressure gauge, safety valve, and thermometer monitor conditions; a timer controls the holding period, after which steam is released and the chamber allowed to cool before opening.
Applications: sterilization of surgical instruments, dressings, culture media, glassware, rubber goods (gloves, tubing), and laboratory/hospital biomedical waste. Not suitable for heat/moisture-sensitive materials (some plastics, sharp cutting-edge instruments, oils/powders steam cannot penetrate).
Sterilization controls:
- Physical controls — autoclave gauges/charts recording temperature, pressure, and time achieved.
- Chemical indicators — autoclave tape (colour change) and the Bowie-Dick test (confirms effective air removal and steam penetration).
- Biological indicators — spore strips of Geobacillus stearothermophilus, processed alongside the load; absence of growth confirms true sterilizing conditions were achieved throughout the load, the most definitive control.