Which of the following is a sterilisation method that uses moist heat under pressure?

• A. Dry heat
• B. Moist heat (steam pressure)
• C. Gas radiation
• D. Ethylene oxide (chemical)

Answer: (B)

Moist heat under pressure is autoclaving. By using steam in a sealed chamber, pressure raises the steam temperature well above 100°C, typically to about 121°C, which rapidly denatures proteins and disrupts cellular structures. This combination—moist heat plus pressure—penetrates loads effectively and kills microorganisms, including spores, in a relatively short cycle. It’s the standard method for sterilizing instruments and many heat-stable items.

Dry heat sterilization, on the other hand, uses hot air without moisture and generally requires higher temperatures and much longer times because heat transfer is slower and steam’s penetrating power isn’t present. Ethylene oxide and other chemical or gas sterilants sterilize at lower temperatures but are chemical methods, not moist heat under pressure. They’re used for heat-sensitive items and involve different, longer cycles with handling considerations.