When working with dangerous chemicals, it is extremely important to have the right safety equipment. Many chemical products are available that have hidden problems. Here is a question I recently got from a customer working with dangerous vapors: What Paint Respirator should I use when spraying Urethane Paint? The information sheet I received about it says to use a NIOSH-approved activated Charcoal cartridge respirator. I would like to use a half mask if possible. You ask a very difficult question, and one without a good answer. As you note, manufacturers of urethane coatings would like you to believe that wearing a mask with organic vapor cartridges and a prefilter will keep you safe from the solvents and isocyanates these paints contain. Obtaining a Material Safety Data Sheet (MSDS) can alert you to the presence of this and other hazards in the coatings you would like to spray. Let’s talk for a minute about isocyanates. They are colorless, tasteless, odorless sensitizing vapors. To be a sensitizer means that, while your first reaction to it may be mild, each subsequent exposure will yield a more serious reaction. Common symptoms are asthma attacks, which may become severe, with some sensitized reactions even known to cause death. Since they are odorless, colorless and tasteless, you will not know that you have been exposed to isocyanates until you react to them. Hence the problem with using cartridge type respirators. If you don’t know when you are beginning to be exposed, how do you know when to change your cartridges? In an industrial setting, air monitoring is required by OSHA to establish the level of solvents in the air as a means to develop a timetable for changing your cartridges. Smaller companies don't do this, let alone hobbyists. My concern with just using a half mask and filters is that you will be exposed to the isocyanates. The only true answer is to use an airline respirator to isolate you from the environment. For more information about airline respirators, read our archived blog post about them here, or check out their page on our website here. A less effective strategy is to employ good ventilation and change cartridges aggressively, maybe as often as every couple of hours of exposure. If you would like to get a little further into it, 3M has a tech support line that can walk you through what I have just said. 3M can be reached at 800-243-4630. As always, don’t hesitate to contact us and ask about your specific situation.