In standard steam sterilization, which option correctly describes the use of temperature, pressure, and time?

• A. Dry heat sterilization at 160°C for 2 hours
• B. Radiation sterilization with gamma rays
• C. Ethylene oxide gas sterilization
• D. Steam under pressure sterilizes biological materials; typical parameters are 121°C at 15 psi for 15–20 minutes

Answer: (D)

Steam sterilization relies on moist heat delivered under pressure. The saturated steam transfers heat rapidly and, because it remains in contact with all surfaces, it denatures microbial proteins effectively, including spores. The pressure raises the boiling point of water, so higher temperatures can be achieved than with simple boiling, which speeds up and deepens sterilization. A standard and widely used cycle uses about 121°C at 15 psi for roughly 15–20 minutes; this combination provides enough heat, moisture, and time for effective sterilization of many common loads, though exact times can vary with load size and contents. Other methods listed—dry heat uses dry air at high temperatures without moisture, radiation uses ionizing gamma rays, and Ethylene oxide gas uses reactive gas—do not describe standard steam sterilization.