During gas sterilization, what humidity level is typically used?

• A. 10 percent
• B. 30 percent
• C. 50 percent
• D. 80 percent

Answer: (B)

During ethylene oxide gas sterilization, controlling humidity is essential because water helps the sterilant interact with microbial cells, improving penetration and the effectiveness of the kill. However, too much moisture can cause condensation, promote hydrolysis of the sterilant, or damage the load and equipment, while too little moisture reduces the sterilant’s activity and penetration.

A moderate relative humidity is used to strike the right balance. About 30% relative humidity provides enough water to facilitate the sterilization reactions without encouraging condensation or other issues. If humidity were significantly higher, condensation and potential equipment/material compatibility problems could arise; if much lower, the effectiveness of the process could be compromised, requiring longer cycles or higher sterilant exposure. Thus, 30% RH is viewed as a typical, practical target for gas sterilization in many protocols.