Volatile Chemicals and Class II Type A2 Recirculated BSCs: How Much is Safe?
Volatile chemicals, while typically used in a fume hood, may sometimes be used in conjunction with biological experiments which often require the use of a biosafety cabinet (BSC). While a 100% exhausted Class II Type B2 cabinet is most often mentioned as the safest option, this is not always possible or may not always be necessary. International safety standards have recommended “minute” amounts of volatiles can safely be used in an internally exhausted Class II Type A2 BSC, but what constitutes “minute” can be left up for interpretation (NSF/ANSI Standard 49, 2014). We have derived a series of equations to calculate the internal concentration, maximum amount allowed safely and the time required for the evacuation of any volatile chemical, shown both by calculation and experimentation. Since each chemical has its own safety limits, it is imperative to perform this calculation for each specific volatile in question. These same principles may be applied to many situations, such as the use of alcohols in BSCs, anesthetics for animal work, or air exchanges within a clean room. While no universal volume of any volatile chemical should be deemed safe to work with in a Type A2 BSC, here we present a tool to find the safe working concentration of each specific chemical that can be used to aid in the most accurate risk assessment.