When using a 3M 2091 Particulate Filter in the field, it is important to change it frequently enough to ensure that you are still getting the necessary protection. I receive many questions asking about the lifetime of these filters. Here is one of the more recent questions: I know it depends on usage and environment, but are the 2091 particulate filters designed to be used and then stored until needed again or are they meant to be used once and then thrown out? If I use this filter for one hour in a basement while working, is the lifespan complete or can I use it for say 20 more hours worth of work? This customer is right: type of usage and the environment that the filter is used in both effect filter life. In general terms, the filter may be used and reused until it is so loaded with particles that breathing resistance is increased to the point of being hard to breathe. However, in the case of toxic dusts, such as lead and asbestos>, you may want to modify that advice. The filter traps particles pretty well, but subsequent handling could dislodge or transfer these particles onto other surfaces or into the air. The filter may still be good, but it may be wise to dispose of in this case as to prevent the spread of toxic dust. As an alternative, the 3M 7093 P100 Hepa filter is enclosed in a plastic case. This keeps the actual filer material out of reach, and should offer better resistance to particle transfer. As always, when working in an environment that requires filter use, know the type of protection you need and take the necessary steps to ensure and maintain that protection. If you are unsure, just ask us!