Skip to main content

5. Safe Handling of MDI Products

MDI and products containing MDI are reactive and potentially hazardous chemicals. MDI should only be handled by knowledgeable and well-trained personnel who thoroughly understand the hazards associated with the transportation, storage, and use of the chemical. Eating, drinking, and the use of tobacco products should not be allowed where MDI is handled or stored. Contaminated clothing must be washed before reuse or discarded if severely contaminated. Never reuse contaminated footwear or leather gloves.

Employee Training and Education

The investment in employee education and training on proper storage and handling procedures for MDI is extremely important. Hazardous situations may be created by poorly trained personnel, even in well-designed
operations. All personnel that may come into contact with MDI products should be included in a hazard
communication training program. Employee training and education programs must include the regulations of all applicable agencies. Local regulations and requirements can be obtained from the local authorities. Additional information is available at: https://polyurethane.americanchemistry.com/Products-Resources-and-Document-Library/ 

Operating procedures, including all safety rules should be reviewed by all personnel regularly. Safety procedures and rules should be posted in work areas accessible to all individuals. Safety equipment should be available and maintained in good working order.

Engineering Considerations

Building design considerations can reduce the potential hazards associated with the storage and handling of MDI. Careful consideration should be given to the design of the building’s ventilation system. MDI aerosols or vapors must be monitored and controlled below applicable regulatory limits. If possible, MDI should be processed within closed systems. There are some applications where this is impractical, however, such as laminate board and composite wood production, spray systems, or laboratory areas. Special consideration should be given to ventilation design and respiratory protection in these applications.

The guidelines established by the Occupational Safety and Health Administration (OSHA), American Conference of Governmental Industrial Hygienists (ACGIH), National Institute for Occupational Safety and Health (NIOSH), and others represent current thinking and are believed to be conservative and protective of occupational workers. Regulations involving hazardous chemicals are continually evolving and thus exposure guidelines are reviewed regularly and modified whenever new information dictates change. It is important that all companies handling MDI products are aware of the current legislative requirements in each jurisdiction.

Additional Precautions

Care should be taken to prevent contact of water with MDI. Water reacts readily with MDI and is the most common contaminant of diisocyanates. The hazard associated with this reaction is the formation of CO2 and the resultant increase of pressure in closed containers. Even small quantities of water can cause significant problems and the following safety recommendations must be observed:

  • Store MDI in a dry environment using dry air or nitrogen pad (dry air or nitrogen should have a dew point below -40°F (-40°C)).
  • Plug and cap all lines leading to and from storage tanks. 
  • Fittings and line connections should be maintained and stored in a dry environment.
  • Do not tightly close any container of MDI that has been, or is suspected of having been, contaminated with water.

Contamination by basic compounds such as caustic soda, amines, or other similar materials must be avoided. The reaction of MDI with these materials may cause the generation of heat and CO2. The liberation of CO2 in tightly closed or restricted vessels or transfer lines may result in violent rupture.

Personal Protective Equipment

Personal protective equipment (PPE) is not an adequate substitute for safe working conditions. However, in many instances including emergency situations, it may be the only means of protecting the worker. Only individuals wearing this equipment are protected. Unprotected personnel should be removed from any work area where there is the potential for exposure to MDI.

Eye Protection

Chemical safety goggles are required for all persons handling MDI, especially where there is the possibility of splashing, spraying, or MDI-coated dust. Cup-type or rubber-framed goggles equipped with the approved impact resistant glass or plastic lens are recommended.

Respiratory Protection

MDI vapor concentrations exceeding PELs may occur. Such occasions include (but are not limited to) the following:

  • Spray operations
  • Opening of tank car hatches, truck man-way covers, or drums that have been heated
  • Connecting or disconnecting of hoses and pipes
  • Equipment operation or repair
  • The breaking or failure of MDI piping or equipment
  • Any spill or leak of MDI that is heated

Personnel must not enter an area where MDI vapor concentrations or aerosols may exceed the recommended exposure limits without appropriate PPE. Personnel who may be exposed to spills and anyone involved in generating MDI aerosols, as in spraying operations, or in the high temperature processing of MDI products, must be provided with adequate respiratory protection.

Respirators must be approved by applicable authorities and a written respiratory protection program with medical surveillance must be implemented. In the United States, an air-purifying respirator (APR) can be used provided that (1) the respirator is equipped with an end-of-service life indicator (ESLI) certified by NIOSH for the contaminant (there is no ESLI for MDI), or (2) if there is no ESLI appropriate for conditions in the workplace, the employer implements a change schedule for canisters or cartridges that is based on objective data that will ensure that canisters and cartridges are changed before the end of their service life. Therefore, an employer must select a cartridge or canister recommended by the manufacturer and must then implement an appropriate change-out schedule. The data relied upon and the information forming the basis of the determination must be included in the employer’s written respiratory program.

If APRs cannot provide appropriate protection, respiratory equipment must be an air-supplied (SAR) or self-contained breathing apparatus (SCBA) with full-face piece operating in pressure-demand or other positive pressure mode.

Respiratory protection equipment must be carefully maintained, inspected, and cleaned regularly. Equipment should be easily accessible, and personnel should be thoroughly trained on the proper selection, maintenance, and use of equipment.

Head, Skin, Hand, and Foot Protection

Head protection should be worn to protect from falling objects, overhead leaks, and splashes. A long sleeved, impervious protective suit should be worn whenever there is possibility of exposure to MDI. Impervious gloves should be worn whenever the possibility of spills or splashes exists.

See the Center for the Polyurethanes Industry (CPI) website (http://www.polyurethane.org) for recommendations on glove permeation data.

Personnel handling MDI drums and cans should wear protective safety shoes with built-in steel toecaps. Rubber overshoes may be worn with ordinary work boots. Never wear uncovered leather shoes. Leather will absorb MDI, making decontamination of leather products such as gloves or shoes difficult.

Surfaces should be thoroughly washed with soap and water after mild contamination.

Fire Hazards

Due to its high flash point (392ºF or 200ºC), liquid MDI does not constitute a severe fire hazard. However, it is important that the proper fire-fighting equipment be available in case it should be needed.

Water spray is effective for extinguishing fires covering large areas. Automatic sprinkler systems may be helpful in certain applications. When water is used to extinguish MDI fires, it should be applied in large amounts. Small amounts may only react with the hot MDI and worsen the fire situation. CO2, protein foam, or dry chemical extinguishers are also effective.

Do not inhale gases or fumes from burning MDI, as they can contain carbon monoxide, nitrogen oxides, MDI, and small amounts of hydrogen cyanide.

Fire fighters should wear self-contained breathing apparatus. Appropriate personal protective equipment (PPE) should be worn including turnout coat, boots, gloves, and helmet.

Back to top