Dry steam? Wet steam? Not in the autoclave

Humidity below 3% produces what is called dry or superheated steam. This steam increases sterilization time because it reduces energy transferability. The superheated steam reduces the humidity to approximately 0%, converting the autoclave into a dry heat oven. Energy transfer is reduced, taking three minutes in the autoclave at 134°C, two hours at 160°C, and thirty minutes at 180°C!

However, humidity greater than 3% produces saturated or wet steam, which requires higher sterilization pressures and temperatures. Moist steam also extends the drying time at the end of the sterilization process. When the load is packed and not intended for immediate use, drying of the load is required at the end of the process.

Autoclave standards and directives allow some flexibility in steam moisture levels, as it is almost impossible to supply optimal steam at a consistent flow rate. Even if conditions are close to optimal, many variables can affect steam when transferred to the autoclave. Chief among them are: weather conditions and temperature; pipe quality, length and structure; drainage stations; and supply of high-quality steam traps.