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Isocyanates in the Workplace

INTRODUCTION

Isocyanates are widely used and found in many industries and occupations, including painting, construction, ship building, upholstery manufacturing and fire fighting. Isocyanates have been used in the United States since the 1950s, and are produced by reacting a primary aliphatic or aromatic amine dissolved in a solvent such as xylene or monochlorobenzene with phosgene dissolved in the same solution. They contain two OASH-NCO cyanato groups attached to an organic radical, and react exothermically with compounds containing active hydrogen atoms to form a polymeric mass (polyurethane). This polyurethane is then used in the production of rigid or flexible foams, surface coatings, paints, electrical wire insulation, adhesives, rubbers and fibers.

The two most common forms of isocyanates are Toluene Diisocyanate (TDI) and Methylene Diphenyl Diisocyanate (MDI). TDI is a liquid at room temperature, and can cause asthma-like conditions when inhaled as an aerosol (such as spray paint). TDI is popular for producing many paints and coatings, along with flexible foam which is used in the making of cushions for automobiles, furniture and mattresses.

MDI is used in the manufacturing of rigid foams, and must be heated before causing asthma-like conditions when inhaled as an aerosol. This makes MDI somewhat less hazardous than TDI, so it has been replacing TDI in certain applications. MDI is commonly used in the production of adhesives, automobile bumpers, shoe soles, coated fabrics and spandex fibers. It can also be found in paints.

Some less common forms of isocyanates include:

Hexamethylene Diisocyanate-HDI
Napthylene Diisocyanate-NDI
Polymethylene Bisphenylisocyanate-PAPI

EXPOSURE LEVELS

The OSHA Permissible Exposure Limit, (PEL) for both TDI and MDI is .02 parts per million of air as a ceiling limit. The ceiling is the highest concentration to which an employee can be exposed. The American Conference of Governmental Industrial Hygienists (ACGIH) recognizes .005 ppm as their Threshold Limit Value (TLV) as an 8-hour TWA and .02 as a Short-Term Exposure Limit (STEL) for both TDI and MDI. Most of the data available on the effects of exposure to isocyanates is for TDI. Because of this, MDI exposure levels are based on TDI's exposure test data.

AIR MONITORING

OSHA test method 42 (for TDI & HDI) and method 47 (for MDI) spell out procedures for personal monitoring of isocyanates. Samples are to be collected by drawing a known volume of air through glass fiber filters with a recommended air volume and sampling rate of 15L at 1 to 2 L per minute.

Conducting continuous monitoring of isocyanates can also be done. Many companies offer single-point monitors that can continuously monitor isocyanates for up to one month. They operate by a electro-optical sensing system, which uses a cassette-like tape. A stain occurs on the tape, and is then read in proportion to the concentration of the isocyanate.

Different cassette tapes are available. Standard play tapes are replaced every two weeks, while extended play tapes last for a month. Datalogging monitors with alarms are also available. These types of monitors are ideal in spray booth operations.

EFFECTS OF OVEREXPOSURE

Exposure to isocyanates can lead to chemical bronchitis and pneumonitis. Symptoms often include coughing, tightness of the chest, shortness of breath, nausea, vomiting, eye and skin irritations, gastric pain, and even possible loss of consciousness.

Continuous overexposure to isocyanates can lead to pulmonary sensitization or "isocyanate asthma." When this occurs, symptoms improve with removal of irritant. However, acute asthma attacks occur on renewed exposure, even when the encounter is very brief or at low levels of isocyanates, and can cause death.

Skin contact can cause inflammation and necrosis which may lead to dermatitis. Wash hands with soap and water immediately upon contact.

PERSONAL PROTECTIVE EQUIPMENT

Proper respiratory protection against isocyanates requires the use of a full-face, continuous flow supplied-air respirator or a self-contained breathing apparatus (SCBA).

Use of a Butyl rubber or SilverShield®/4H glove will give adequate hand protection from isocyanates.

For help selecting the right protective clothing to use with isocyanates, contact our Safety TECHline™ Technical Support at 1-800-356-2501 or e-mail them at techsvc@labsafety.com.

Commonly Asked Questions

Sources for More Information

Willson Technical Services Brief, June 27, 1996.

American Conference of Governmental Industrial Hygienists "TLV's and BEI's," 2007.

American Journal of Industrial Medicine 13:331-349 (1988) "Isocyanates and Respiratory Disease Current Status"

Clinical Allergy. 1984, Volume 14, p.329-339.

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