Aliphatic isocyanates are commonly used to formulate polyurethanes (PU) for a variety of coating applications. Every user of aliphatic isocyanates must be familiar with the potential hazards and have the knowledge needed to safely handle and use these products. The potential to experience health effects depends on the exposure level (e.g., airborne concentration in the breathing zone, volume of liquid/spray mist in contact with unprotected skin), duration of exposure, and other factors, including individual susceptibility. Polyurethane coating systems can be used safely in the work environment with appropriate engineering controls, work practice controls, good housekeeping/hygiene practices, and personal protective equipment (PPE).

In two-component (2K) solvent-borne PU coatings, aliphatic polyisocyanates based on hexamethylene diisocyanate (HDI) are the most common. HDI polyisocyanates typically have the CAS# 28182-81-2, while 1,6-hexamethylene diisocyanate monomer has the CAS #822-06-0. HDI polyisocyanates usually contain small amounts of residual HDI monomer, below one percent.

The potential health hazards associated with isocyanates are:

• skin and eye irritation

• respiratory tract irritation

• allergic skin reaction

• allergic respiratory reaction, asthma-like symptoms or breathing difficulties

Respiratory system health effects may occur when isocyanate vapors or mists exist at airborne concentrations above the exposure limits or guidelines. The health effects associated with the skin may occur with repeated unprotected contact with an isocyanate-containing liquid or spray mist. These health effects can be controlled with proper engineering controls (i.e., local exhaust ventilation), use of personal protective equipment (PPE), and good work practices (i.e., proper housekeeping, wash facilities, preventing consumption of food/drinks in the work area). Consult the Safety Data Sheet (SDS) from the coating supplier for more details on the health effects described above and symptoms that may be associated with them. Read on for a few tips to help control potential hazards during PU spray coating applications during spray application.

Engineering Controls

Hazard control of vapor and spray mist is ideally accomplished through engineering controls. There are several engineering controls available to reduce exposure including local exhaust ventilation (LEV), isolation principles, and general ventilation. The most effective engineering control approach is a properly designed and ventilated enclosure. Effective local exhaust ventilation (LEV) should be provided to minimize exposure to airborne spray mist and vapors. Guidance on properly designed and operated LEV systems is available from the following resource: Industrial Ventilation: A Manual of Recommended Practice for Design, published by the American Conference of Governmental Industrial Hygienists (ACGIH).

PPE

Because isocyanates are sensitizing agents, spray applying polyurethane systems requires the user to be fully protected from contact with the uncured material (i.e., from spray mist or spray drift).

Recommendations on PPE are as follows:

• Eye protection

• Gloves: nitrile rubber, butyl rubber, or neoprene

• Coveralls: a full-body disposable type coverall or protective suit with head covering

• Safety shoes

• Respirator: either a tight-fitting full facepiece air-purifying respirator (APR) equipped with combination organic vapor cartridges and particulate pre-filters (OV/P95) or a supplied-air respirator (SAR), such as a loose-fitting hood/helmet operated in a continuous flow mode

Note: For automated spray applications, the selection of a respirator for an employee depends upon the airborne concentration of the isocyanate or the exposure level in the breathing zone of the employee. Exposure is dependent upon ventilation controls established by the employer and the duration of time the employee overseeing the automated spray application spends in the immediate spray area. In some situations, workers not involved in performing manual spray applications but who may need to enter a spray area for any reason for short periods of time may need to wear a half facepiece air-purifying respirator equipped with combination OV/P95 cartridges. All respiratory protection must be used in accordance with the OSHA Respirator Standard, 29 CFR 1910.134. You should always consult the coating supplier’s safety data sheet to ensure proper PPE for all components in the product.

Data from OSHA Isocyanate NEP

OSHA develops National Emphasis Programs (NEPs) to focus outreach efforts and enforcement on specific hazards in a particular industry for a three year period. According to OSHA, the isocyanate NEP was developed to focus resources on the reduction of worker dermal and respiratory exposure to isocyanates.

The data that OSHA has shared with industry on the NEP has shown that the top four industries that exceeded the occupational exposure limit for HDI polyisocyanate include:

• General Automotive (47.2%)

• Aircraft Manufacturing (20.7%)

• Construction Machinery Manufacturing (15.1%)

• Painting and Wall Covering Manufacturing (9.4%)

The most common OSHA standards cited under the NEP include:

• Respiratory Protection

• Hazard Communication

• Personal Protective Equipment

These industries commonly use HDI polyisocyantes in spray painting applications. Because spray applications may generate aerosols, it is common to find high levels of HDI polyisocyanates in these scenarios. Because of this, the use of the engineering controls and PPE is critically important to reduce the exposure hazards from airborne HDI polyisocyanates.

Summary

Polyurethane coatings have been used safely in demanding high-performance applications for many decades (automotive, construction, aviation, military, etc.). The applicator must be aware of potential health hazards of isocyanate containing coatings and must employ the necessary controls in order to ensure a safe work environment.

About the Authors:

Ahren Olson has been the marketing manager for Corrosion Protection with Covestro LLC in Pittsburgh, Pa for 12 years. He has held both technical and marketing positions in the areas of automotive, construction, and protective coatings.

Scott Ecoff has been an industrial hygienist with Covestro for five years and is a member of the Product Safety and Regulatory Affairs group. A significant responsibility of this group is product stewardship.

Lisa Marie Nespoli has been a product safety and stewardship manager in the Product Safety and Regulatory Affairs group at Covestro for seven years. Lisa Marie provides guidance and expertise on product health, safety, and stewardship to Covestro’s businesses and leadership teams, and she is responsible for developing and implementing product stewardship processes. For more information, please visit www.productsafetyfirst.covestro.com