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I agree with CNKS. My guess is that his thoughts are reasonable for the brush painting, especially if it is done outside with plenty of natural ventilation. The label on a PPG OMNI hardener can says "Use with adequate ventilation. Where vapors or overspray are present, use a positive-pressure air-supplied respirator for the entire time of spraying and until all vapors and mists are gone." The MSDS for the same material indicates similarly. It's pretty clear that the fumes are a problem along with the atomized spray mists. I've read that paint mixing (with isos) can be done with a cartridge respirator because of the lower exposure levels. See link. I do all my own painting, including the mixing, outside where natural ventilation is plentiful. I only do work for myself or friends so I can schedule the work around the weather. I use an air-supplied respirator when actually spraying and remove myself from the immediate area afterwards. The only brush work that I do is with very small quantities in a paper cup for touching up bolt heads, nuts, etc with an artist's brush. I don't use a respirator at all for that but then again, it is also done outside and the quantity is very limited. I doubt that you will find a definitive answer for brush painting significant areas. It wouldn't be done at all in the automotive industry where these materials are primarily used. The experience in that area would therefore be essentially nil. My own thoughts would be to use a cartridge respirator (fresh cartridges) and do it outside if at all possible to minimize your exposure. Or use lots of mechanical ventilation, together with the respirator, if done inside. That would provide at least some protection. You are unlikely to find a chemical cartridge from ANY manufacturer that is recommended specifically for isocyanates. The variables in usage of that type of respirator are just too many to assure a high degree of safety, considering the particular hazards of those materials. I am assuming that you do not have a beard that would preclude a proper cartridge respirator fit. Not an expert in this matter...just giving an opinion. Rod
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