CNKS...

• PDF

OSHA has a lot of linked material relative to isocyanates. They have a lot of regulations applicable to body shops that is interesting but not really reasonable to implement for most DIY operations. NIOSH is one of the key agencies who develop and recommend permissible exposure levels although I don't believe they have any actual regulatory authority. HDI is one of the several isocyanate compounds used in paint hardeners and activators. From what I have seen and read about others, HDI is pretty much typical of them all. They seem to be treated as a family of hazardous compounds. NIOSH has published this on HDI. They recommend supplied air even when exposures are less than the generally accepted one (0.005 ppm). More from NIOSH here. They clearly recommend supplied air even inside a well operating professional booth. Similarly on HDI, the New Jersey Department of Public Health has this to say.

Still more from NIOSH here with the following excerpted text:

Whenever there is potential for exposure
to diisocyanates, even concentrations
below the NIOSH REL, NIOSH recommends
that employees be supplied with
supplied-air respiratory protection.
(Negative pressure air-purifying respirators
are not recommended since
diisocyanates have poor odor warning
properties.) Also, there should be a
respiratory protection program.

The California Department of Health Services has this to say. The Saskatchewan Department of Labor has this to say. PPG's official position is here. DuPont's is similar and explicit in their applicable MSDS.

I personally think the evidence for supplied air when using iso-containing materials is overwhelming despite some pro painter's insistence to the contrary. I also think that it may be even more important for the DIY than for the pro painter who works in a booth. There are more unknowns and variables with a DIY, even when he works outside. Pro painter's opinions are important and I respect them. However, I will always give more weight to the independent agencies who have the actual responsibility for recommending safe work practices for all. I'll certainly agree that the paint manufacturer's are generally conservative in their recommendations. They have every reason to be. What gets me is the whole thing is so easy to correct. No DIY has to use hardeners when painting his tractor. It's entirely optional. There are alternative paints that do not require them. Inferior you say? Sure they are. But they were perfectly satisfactory before isos were ever developed and can be put to good use today. Indeed, they are as good, sometimes better than the original OEM paint that was used on most vintage tractors. If someone wants to get better performance from paint, they can evaluate the health risks for themselves as well as the cost of the excellent protection provided by supplied air. Arguments over iso exposure levels are academic anyway. It's simply too easy just to go with supplied air and have little further concern about the whole matter. I learned that the hard way for myself a long time ago. Best money I ever spent. But to each his own.

Understand. Everyone here is trying to help others. Agreed this is not a PPG or DuPont promo site. However the issues about isocyanates are applicable to all other manufacturers also. I refer to both PPG and DuPont only because I have used some of their products and am familiar with them. Other manufacturers such as MS, SW, BASF, Valspar, etc. make equally good products but I am unable to discuss them in detail because I have never used them. I can read and understand their tech sheets but I have no personal experience with actually using their products. I do agree with CNKS though that as far as basic paint chemistry goes, one can make some observations without having used the product. Alkyds are alkyds and urethanes are urethanes no matter who makes them. And in general, the price increases as the performance does. If alkyds presented similar performance to urethanes, the auto OEMs would still be using them since they are cheaper. Yes, I agree that it is up to the person on the other end to evaluate the safety issues involved with any procedure or product. Many DIYs however may not be that familiar with automotive paints and the additives to be used. That's not their fault. They may have never heard of isocyanates, MSDS, tech sheets, 2K products etc simply because they are not familiar with automotive paints. From that perspective it makes sense to me that when recommendations are made to obvious novices, that they also be reminded about the safety issues involved with hardeners. They don't have to take my recommendations or anyone elses. They are free to do as they please. But at least they will be made aware of a potential problem. To blindly recommend adding hardener to a paint to "make it better" to an obvious novice is doing them no service at all without also advising about the special health-safety protection that is normally recommended. Some professionals have always used a cartridge mask and swear by them, even for isos. Different people are effected differently. Some may have no reactions at all. Others, like myself, may have severe reactions the first time out. It only took me two cars without supplied air to get off my rear end and spend the money for it. Perhaps that's just me being unlucky but I like to be able to breathe freely after using that stuff. A couple of nights with abnormal shortness of breath and coughing can focus the mind a lot. The better paint performance is not worth it if one has to endure that. Perhaps that's why I am a stickler for recommending supplied air to novices. I know first hand what is possible and how to easily avoid it. Others will be more fortunate and can get by with cartridges indefinitely. In any event - peace!

Hardener does increase gloss, but it does not prevent fading. There are toxic chemicals all around us. People should protect themselves whenever they can. Isocyanates are one of the worst, and can be deadly -- but you can protect yourself from them. Chemicals that may be dangerous that we encounter in everyday life, you can't protect yourself from unless you live in a bubble.

As you have noticed, I am somewhat of a blunt person -- I will continue to attempt to explain the differences between paints -- I don't need 30 years of experience to do that, I have observed it first hand on the vehicles I have bought, beginning with a 1954 Plymouth, ending with a 2005 GMC pickup. The difference is remarkable. You will note that I have never actually told people HOW to paint -- just what to use.