Methylene Chloride Facts No. 6
Suggested Engineering Controls for Flexible Polyurethane Foam Manufacturers

Occupational Safety and Health Administration

On January 10, 1997, the Occupational Safety and Health Administration (OSHA) issued a standard that lowered the limit on worker exposures to methylene chloride (MC). This new standard greatly reduces the chance of developing health problems from working in facilities that use MC.

Worker exposures to MC occur mainly through breathing its vapors. MC can also pass through workers' skin if it gets on their body or clothes. Occasionally, workers can swallow small amounts of MC if they don't wash their face and hands before eating, or if they eat in contaminated work areas. Short-term exposure to high levels of MC can cause dizziness, headaches, a lack of coordination, and irritation of the skin, eyes, mucous membranes, and respiratory system. Long-term exposure causes cancer in laboratory animals. Studies in workers suggest an association between MC exposures and certain types of cancer. OSHA considers MC to be a potential occupational carcinogen. Exposure to MC may also make the symptoms of heart disease (e.g., chest pains, angina) worse.

Many facilities that manufacture flexible polyurethane foam (p-foam) use MC as a blowing agent to make soft foam. Most of these facilities will need to use engineering controls to reduce worker exposures to MC to acceptable levels. The following describes some engineering controls that you may find helpful in reducing worker exposures to MC in your facility.

Monitoring

Employers must monitor worker exposures to MC to determine whether engineering controls are necessary. Where engineering controls are already in place, employers must monitor worker exposures to determine the effectiveness of the controls and whether or not improvements or additional control methods are needed.  For additional information on monitoring for MC, see OSHA Methylene Chloride Facts No. 01.

Tunnel Controls

Worker exposures to MC are highest near the tunnel where p-foam is made. MC vapors come from the front end of the tunnel where the raw materials are poured and mixed, from the bottom end of the tunnel where the foam is cut, and from leaks and openings in the tunnel. Most tunnels have local exhaust ventilation (LEV) units.

Note: Check with the appropriate local, county, or state environmental office to make sure you have the required permits if you will be exhausting MC directly outside.

If monitoring results indicate that worker exposures to MC are above established limits when working near the tunnel, and new or improved controls are necessary, consider using one or more of the following control options:

  • Install an LEV unit in the tunnel. Note: A make-up air system is required to ensure the proper operation of the LEV.
  • Increase the exhaust capacity of the tunnel's ventilation system.
  • Decrease the distance between the p-foam and the exhaust system. This will allow the LEV to remove more MC. You can lower the tunnel's ceiling or change the location of the exhaust inlets (e.g., use a slot exhaust at the inner perimeter of the tunnel).
  • Use a tunnel with two open ends that allow make-up air to exhaust MC vapors.
  • Use disposable tunnel liners so that workers do not need to use MC to clean tunnel walls.
  • Do not use aluminum in any equipment used to handle, store, or process MC. MC corrodes aluminum. If aluminum parts fail, spills will occur.
  • If MC is used to flush the mixing head and delivery hoses, do this in a closed loop to the MC container so the solvent can be collected and reused rather than being allowed to evaporate into the workplace. Mixing head parts can also be soaked in MC in closed containers. If this is not feasible, leave the tunnel fan on and conduct cleaning operations in the tunnel.

Saw Operator Controls

The saw operator is often exposed to high levels of MC, so additional controls may be necessary to protect these workers. If monitoring results indicate that saw operator exposures to MC are above established limits, and new or improved controls are necessary, consider using one or more of the following control options:

  • Mount a slot exhaust system on the guide tracks of the saw. Use a flexible hose to connect this system to the exhaust conduit. This will allow the exhaust system to move with the saw as the saw cuts the foam.
  • Provide the saw operator with a fresh air island. The fresh air island brings fresh air in from above the worker, blows it past the worker's breathing area, and exhausts it through the floor. The air velocity of the fresh air island must be greater than velocity of the air inside the tunnel for this strategy to work.

Cooling Area Control Options

As the foam cools, it releases MC. Most MC is released during the first few hours of cooling. If monitoring results indicate that worker exposures to MC are above established limits when working in or near the cooling area, and new or improved controls are necessary, consider using one or more of the following control options:

  • Allow p-foam to cool outside in canopies or open structures if possible to obtain natural ventilation.
  • Install a general ventilation system. Place the exhaust fans near the cooling p-foam. [General ventilation does not confine MC vapors to one area, so it usually does not protect workers as well as LEV.]
  • Turn on general ventilation at least an hour before work begins or leave it on overnight.
  • Provide a ventilated, conditioned-air cab for the forklift and/or crane operator. A cab provides continuous protection for these workers when they are in the tunnel area and the cooling and storage area.

Additional Monitoring

Always remember to monitor worker exposures again after you install new engineering controls to determine whether the controls are working properly and reducing exposures to acceptable levels.

Substitutes

Using blowing agents other than MC is another way to reduce MC exposure.

  • Acetone produces high quality soft foams and can be used instead of MC. Acetone is extremely flammable, so be sure to take appropriate precautions.
  • Some facilities use variable pressure when blowing foam (i.e., the foam is blown in a vacuum). This eliminates the need to use auxiliary blowing agents such as MC.

Keep in mind that substitutes may also present health and safety hazards to workers. Always select substitutes that reduce hazards, and always refer to the substitute's material safety data sheet to find out about any control measures and protective equipment you must use to protect workers.

Respirators

If engineering controls and work practices do not reduce MC exposures to an acceptable level, you must give workers supplied-air respirators. Respirators are the least preferred method of controlling employee exposures. Supplied-air respirators must have a clean air supply through the use of compressed air tanks containing air meeting at least the requirements for Grade D breathing air, or a breathing air type compressor with the air intake located in an area with a clean air supply.

CAUTION: Filter cartridge respirators cannot be used because MC can pass through available cartridges leaving respirator wearers unprotected.

Additional Resources

Visit the On-Site Consultation Program page for information on how to request a free, confidential visit from a consultant to help identify ways to improve safety and health at your workplace.