Tukz, since you mentioned the backseat of a car, I assume that you are allowing staff to take thiers home. My staff have to leave the fanny pack here, and get one when they go on duty. All masks in the on duty fanny packs are brand new, never been used. I keep a separate supply of fanny packs and masks for training use.
If I am doing a skill test on a guard while on duty, I carry a training mask with me to hand them when they get out of the water after the rescue. So yes, the masks do get exposed to chlorinated water during occasional on duty skill testing or simple rescues. I continue to rotate out the new masks to training masks, and any newly ordered masks go to the on duty fanny packs.
Haven't had a large problem with defective Easy Seal masks, but since we just ordered some new ones we will check them over good!