I bought these while using polyurethane on a floor in the middle of winter with the charcoal filters when I couldn't get much ventilation . Never even got a wiff of toxic fumes. My only warning would be that because you don't smell the fumes can keep you unaware of the lack of oxygen in the room. So be careful and don't work long in a closed space. In fact tell your customer that you will come back in spring when you can open windows. Comfortable to wear and easy to use.