Methylene Chloride Facts No. 3
Suggested Engineering Controls for Furniture Refinishers

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 furniture refinishing facilities using products that contain MC will need to implement 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.

Ventilation Systems

Local exhaust ventilation (LEV) is often the best way to reduce MC exposures to acceptable levels. LEV units capture vapors at the source and remove them from the work area. A typical LEV unit has a metal hood, fan, ductwork, and a make-up air system. Note: A make-up air system is required to ensure the proper operation of the LEV.

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

  • Increase the exhaust capacity of the ventilation system.
  • Install a remote electrical switch to turn on the LEV, rather than a switch on the unit. This way, workers can turn on the LEV without going near the MC.

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.

General (or dilution) ventilation uses fans or open windows to move clean air through the work area. This does not confine MC vapors to one area, so it usually does not protect workers as well as LEV. General ventilation can sometimes reduce MC to acceptable levels in areas used only for minimal manual stripping operations.

  • Store MC in closed containers near general dilution ventilation.
  • Turn on general ventilation at least an hour before work begins or leave it on overnight.

Engineering Control Options for Tanks

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

  • Install a wall-mounted LEV next to all tanks.
  • Install an exhaust hood over the tank and/or slot hoods on each side.
  • Put a perforated plate about 9 inches from the bottom of each spraying tank with a down draft ventilation system to pull air through the plate. The plate raises the furniture being worked on so that the operator does not have to bend over the tank. The plate also reduces the amount of MC that evaporates from the tank.
  • Put a turntable inside the spraying tank so that furniture in the tank can be rotated. This way the workers can stay in one spot when applying stripping solution. Having the worker in one spot makes it easier to provide fresh air to the worker.
  • When transferring stripping solution from a container to a tank, use a vapor return line to create a 'closed loop' and contain MC vapors.
  • Use long-handled brushes for scrubbing to keep workers as far out of the tank as possible.

Engineering Control Options for the Rinse Area

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

  • Install a wall-mounted LEV in the rinse area.
  • To make the LEV more effective, isolate the rinse area, by using a curtain or by putting it in a separate room.
  • Install a sneeze shield in the rinse area. This can help to contain the operation and reduce splashing.

Other Engineering Tips

  • Keep dip tanks and spraying tanks in an isolated area (separate from other work areas).
  • Use a belt heater to keep stripping solution at the appropriate temperature (often around 70F). At this temperature, wax in the solution will form a vapor barrier that prevents the solution from evaporating too quickly. If the temperature is too high or too low, the wax will not form a vapor barrier.
  • Do not use aluminum in any equipment used to handle, store, or process MC. MC corrodes aluminum. If aluminum parts fail, spills will occur.
  • Add a four-inch layer of water on top of the MC in the dip tank to form a vapor barrier.
  • Use closed or covered MC containers that can connect to the spraying table. This way, MC vapors from the containers flow directly into the trough, where the exhaust system can remove them.

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 furniture stripping solutions that do not contain MC is another way to reduce MC exposure.

  • n-Methyl-pyrrolidone (NMP) can remove clear and pigmented nitrocellulose lacquers, conventional varnish, and all types of water-borne coatings as well as MC.
  • Methanol, acetone, and toluene can remove many finishes and paints. These substitutes are extremely flammable, so be sure to take appropriate precautions.

Also, using diluted stripping solutions (i.e., 50 percent MC mixture) in conjunction with other controls such as LEV is a good way to reduce employee exposure. Keep in mind that substitute stripping solutions 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 for 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.