Hi guys,

I would like to dispel some incorrect information about isocyanantes, their mode of operation in out bodies and how the selection of PPE comes about. To give you some background, this area is my carrer - I'm a Certified Industrial Hygienist and got my masters in Environmental Sciences (Industrial Hygiene). Disclaimer: This in no way means that I'm NOT full of _ _ _ _ on other areas of jet modeling. Anyways - this I do know. About 2 years ago, I did a bunch of research (and a paper) into the medical/toxicological study literature on Iso's and Cyanoacrylates. As luck would have it, Bayer Chemicals and 3M was doing a high-level technical class on iso hazards at a professional development seminar I went to. I participated in that as well. Here's what I found out and know:

Isocyanates are not technically !QUOT!cumulative!QUOT! like lead poisoning, but are in a class of hazards called !QUOT!sensitizers!QUOT!. They do not collect in your body, but rather your body develops an allergic reaction to them over repeated exposures. There's no specific number of exposures that leads to a person becoming sensitized. Once sensitized, you will have a systemic allergic reaction (not the typical runny nose/sneezing). The reaction is just as was described earlier - bronchoconstriction, etc. can't breathe. As far as is known from studies thus far, once sensitized, you're always sensitized. there appears to be no other long term affect known yet (always subject to change). Most adverse reactions described in the literature do not involve death - but there have been a very few. A person's tendency to react is varies due to age, health and most markedly due to race for some reason.

Not all Iso's are created equal. TDI is the worst actor and the paint companies have by and large have moved away from it. The poly-isocyanates demonstrate the least sensitivity potential from those I've reviewed. Skin sensitivity has only been demonstrated in animals with direct painting of TDI on the skin and never demonstrated in humans. Could it happen? Who knows, but I'm not going to test it. Some of the other health effects on the paint cans are not due to the iso's, but rather the solvents and carrier chemicals which have a detrimental effect on liver, kidneys and nervous system.

PPE:
3M did a study in which they took their respirator cartridges and forced air w/typical iso concentrations through them and had sensors on the other side to see when breakthrough would occur. Bottom line was that a chemical (specifically an Organic Vapor) cartridge alone showed very quick break through but an OV cartridge with a HEPA pre-filter gave very good protection on the order of hours. Here's the rub: you can not smell iso's at the ppm level that they are considered to be potentially hazardous so you have no warning properties. NIOSH respirator decision logic then dictates you use supplied air with such chemicals if the cartridge has no end-of-service life indicator. Paint companies will not go against the NIOSH recommendations. David was right on the money about your cartridges to - you open a chemical cartridge and it's got at best a week's life span under perfectly low chemical exposure and super low humidity (say Arizona?). In the Gulf Coast, where I live, the life span is measured in hours with little to no chemical exposure. 3M is very confident that a HEPA pre-filtered, fresh OV cartridge provides protection, but they can not recommend it due to the technical limitations and so they don't.

Gloves - As a chemical safety geek, I'm proud of you guys; Nitrile gloves ARE the way to go for almost all of your painting needs. Latex is porous and absorbent of solvents. You can buy the nitrile gloves researchers use in laboratories that are as thin as latex exam gloves and they'll do just fine as long as you're not dunking your hand in the paint. Just make sure they are the type that have SOME chemical resistance.

What about residue after painting? After mixing, Iso's polymerize fairly rapidly and loose activity. They basically turn into plastic. Humidity also causes iso's to polymerize without mixing. The tests 3M/Bayer and others have done showed no free isocyanates basically within a few hours after painting. This, they think may also be one of the reasons why we don't see more very bad reactions to the stuff, kind of limiting the exposure.

Chuck Carlisle, CIH, CSP, CHMM