Methylene Chloride Facts No. 8
Suggested Engineering Controls for Cold Degreasing and Other Cold Cleaning Operations

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 perform cold degreasing and other cold cleaning operations use products that contain MC. Some 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.

Ventilation

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 LEV systems where MC is stored or used to remove MC vapors before they reach a worker (for example, at degreasing work stations and near cold cleaning operations ).
  • Install a remote electrical switch to turn on the LEV, rather than putting a switch on the unit. This way, workers can turn on the LEV without going near the MC.
  • Perform manual cold cleaning operations within a ventilated enclosure. This type of LEV generally has an even greater capture efficiency since the enclosure contains 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 does not protect workers as well as LEV. General ventilation can sometimes reduce MC to acceptable levels in areas used for manual cold cleaning.

  • 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 an LEV over the degreasing tank. The LEV should have a slotted hood (either one-sided or multiple-sided).
  • Install a cover on the degreasing tank. Covers should slide open. Covers that open upward on hinges can cause solvent vapors to be pulled out of the tank, which can expose workers to high levels of MC. Note: If covers must open upwards, they should be opened slowly to reduce as much as possible the amount of MC pulled out.
  • Ensure that the LEV system is running before covers are opened.
  • Design covers so that they can be opened from a distance away from the tank, either by mechanical or powered means.
  • Keep the tank covered except when loading and unloading parts.
  • Add a four-inch layer of water on top of the MC in dip tanks to form a vapor barrier.
  • Install an automatic hoist system to load and unload the degreasing tank.
  • Put a turntable inside the degreasing tank so that parts in the tank can be rotated. This way the workers can stay in one spot when applying cleaning solution. Having the worker in one spot makes it easier to provide fresh air to the worker.
  • Put a shelf about 9 inches from the bottom of each degreasing tank. The shelf raises the parts being worked on so that the operator does not have to bend over the tank to scrub them. The plate also reduces the amount of MC that evaporates from the tank.
  • When transferring cleaning solution from a container to the tank, use a vapor return line to create a 'closed loop' and contain MC vapors.
  • Provide long-handled tools for scrubbing so that workers do not have to lean over the tank and breathe MC vapors.

Other Engineering Tips

  • Do not use aluminum in any equipment used to handle, store, or process MC. MC corrodes aluminum. If aluminum parts fail, spills will occur.
  • Keep the degreasing tank in an isolated area (separate from other work areas).

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 cleaning solvents other than MC is another way to reduce MC exposure.

  • Aqueous cleaning can be used as a substitute for some degreasing operations. Aqueous cleaning uses detergents in hot water to remove oil and grease from metal parts.

Keep in mind that substitutes may also present health and safety hazards to workers. In addition, substitutes may require compliance with environmental requirements such as wastewater treatment. 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 or the environment.

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.