COMDTINST 6260.30A
4. DISCUSSION. Isocyanate-containing coatings such as polyurethane, polyurea or
polyurethane/polyurea hybrid coatings provide a weather resistant, colorfast topcoat
for protecting surfaces from abrasion and corrosion. These coatings are described as
one-part or two-part systems. The one-part polyurethane coating is further classified
as either moisture-cured or heat-cured. These coatings present no health hazard once
cured; however, they do present a health hazard during preparation, application and
curing stage due to the release of isocyanate vapors and mists. Two-part systems
present the greatest potential for exposure to isocyanate vapors and mists.
The isocyanates found in these coatings include Toluene Diisocyanate (TDI),
Hexamethylene Diisocyanate (HDI), and Diphenylmethane Diisocyanate or
Methylene bisphenyl isocyanate (MDI).
5. DEFINITIONS. For the purposes of this Instruction, the following terms are defined.
a. Heat-Cured Polyurethane System. Either a one-part or two-part system where
heat must be used to release a chemical agent (called blocking agent) from
polyisocyanate. In the absence of the blocking agent, polyisocyanate then reacts
with a polyol.
b. Moisture-Cured Polyurethane. One-part polyurethane in which curing process
occurs by the reaction of polyisocyanate with moisture present in the atmosphere.
This reaction results in the production of amine compound, which further reacts
with the remaining isocyanate to form urea.
c. One-Part System. A system where the isocyanates are pre-polymerized, so that
very little of free isocyanate remains.
d. Polyurea. The product of a reaction between a polyisocyanate and amine
terminated resin compounds.
e. Polyurethane. The product from the reaction between polyisocyanate and a
polyol.
f. Polyurethane/Polyurea Hybrid. The result of a chemical reaction between
polyisocyanate and a mixture of polyol and amine terminated resins.
g. Two-Part System. The two-part systems contain un-reacted polyisocyanate and a
polyol or polyamide resin in separate containers, which are mixed together
immediately preceding application.
6. EXPOSURE AND HEALTH EFFECTS.
a. Health Effects. Isocyanate vapors cause irritation of the skin, eyes, and
respiratory tract. In addition, persons exposed to isocyanates may become
sensitized (allergic to isocyanates). It may also cause persons who have skin
exposure to become sensitized and develop allergic dermatitis. Once sensitized,
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