how long does 1 filter last?

If ever used in an oily environment, change after 40 hours of use or 30 days, whichever comes first. If oil-based particulates are never filtered, change when breathing becomes difficult, dirty, or hygiene.

Unfortunately there are too many variables to have a set amount of time. We use the 3-D's which is when the mask is damaged, dirty, or difficult to breathe through you will want to replace the filter. Thanks for asking!