Written By: Robert E. Sheriff, MS, CIH, CSP, President
April 27, 2017
The health effects of exposure to isocyanates include asthma, skin rashes/dermatitis, irritation of mucous membranes (eyes, nose and throat) and chemical bronchitis. The most common commercial isocyanates are the diisocyanates—toluene diisocyanate (TDI), methylene bisphenyl diisocyanate (MDI) and hexamethylene diisocyanate (HDI).
These isocyanates are generally used to make rigid and durable surface coatings as a substitute for oil/solvent based paints and coatings. They also have application in insulation foams, wire coatings, adhesives and rubber-like compounds.
The greatest danger related to isocyanate exposure is an acute asthmatic attack. Equally important is that when an individual becomes sensitized to an isocyanate, they cannot tolerate levels even far lower than what caused the initial reaction. Often sensitized individuals cannot work around the isocyanates at all—even minute amounts like walking into a paint store or getting into a newly painted car.
Because of the potential for isocyanate sensitization, the best control is prevention of any exposure—certainly not above the following limits:
OSHA Ceiling Limits (No Exposure Above This Level)
MDI – 0.02 ppm
TDI – 0.02 ppm
NIOSH Recommended Limit for Isocyanates
HDI – 0.005 ppm REL (Recommended Exposure Limit) – 8 hours
MDI – 0.005 ppm REL – 8 hours
TDI – Lowest Feasible Concentration
ACGIH Recommended Limits
TDI – 0.001 ppm – 8 hours
0.005 ppm – STEL (15 minutes)
MDI – 0.005 ppm – 8 hours
HDI – 0.005 ppm – 8 hours
As mentioned above, the best approach is prevention of any detectable worker exposure—especially TDI which is considered the most toxic of the commonly available diisocyanates used in industry.
We recommend monitoring of workers very soon after the introduction of an isocyanate in the workplace and at regular intervals thereafter, (OSHA usually recommends every 3 years), and when there is any change in the process.
This information should be communicated to employees as part of the OSHA required annual Hazard Communication Training (29CFR1910.1200).
Employees can also wear respiratory protection on a voluntary basis—as long as the EMPLOYER makes sure that it is the proper respirator (Voluntary Use of Respiratory Protection is outlined in Appendix D of the Respiratory Protection Standard 29CFR1910.134).
Monitoring of potential isocyanates exposure to workers should be performed by an Industrial Hygienist and samples analyzed by an AIHA Certified Laboratory.
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