A small room with an area of not less than $3text{m}^2$, whose entrance and exit doors shall not be opened simultaneously, which is supplied with clean air and reaches the same cleanliness class as the area to be entered (but not exceeding Class 1 000). More effective than an airlock.

【Reference】 Air showers are commonly used in industrial cleanrooms, pharmaceutical plants and other places where dust particle contamination is controlled; based on testing and actual use, their effectiveness is not ideal. They are generally not applicable to biological cleanrooms where the control of microorganisms is the primary concern.