Methylene Chloride Facts No. 10
Suggested Engineering Controls for Vapor Degreasing 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.

Certain workers at facilities that perform open-top and/or conveyorized vapor degreasing operations are at risk of being exposed to high levels of 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:

  • Install LEV systems where MC is stored or used to remove MC vapors before they reach a worker (for example, install a lip exhaust system at the degreasing tank).
  • Increase the exhaust capacity of the LEV system.
  • 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.

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.

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:

  • When transferring MC cleaning solution from a container to the tank, use a vapor return line to create a 'closed loop' and contain MC vapors.
  • Install a cover on the degreasing tank. Covers should slide or roll 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 limit the amount of MC pulled out.
  • Design covers so that they can be opened from a distance away from the tank, either by mechanical or powered means.
  • Install an automatic hoist system to load and unload the degreasing tank.
  • Install a canopy system that moves with the rack during loading and unloading operations and covers the top of the tank. Make the canopy out of clear material or with viewing ports to allow operators to monitor the degreasing process. If possible, attach glove ports to enable the operators to spray parts without exposure to MC. Parts should be sprayed below the Vapor level. The canopy will also prevent workers from leaning over the tank.
  • Provide means for spraying below vapor level so that workers do not have to lean over the tank and breathe MC vapors.
  • Install a freeboard on the degreaser, or extend the existing freeboard, to ensure a proper freeboard ratio, to reduce the amount of MC vapors that enter the work area.
  • Install a freeboard chiller system to provide a cool, dry layer of air above the vapor zone. The air layer will help contain MC vapors.
  • Install and maintain adequate water separators on all degreasers. Water can form a boiling mixture with MC vapors causing MC to enter the work area. Water separators eliminate water that gets into the degreaser system.
  • Ensure that the degreaser's liquid and vapor level indicators are working properly at all times.
  • Use tanks with small openings so that cleaning does not require workers to enter the degreaser. This will prevent unnecessary worker exposure to confined space hazards.
  • Ensure that the degreaser's drain line starts from recessed portions of each compartment bottom to facilitate complete drainage of MC.
  • Keep the degreasing tank in an isolated area (separate from other work areas) and away from open windows or doors, heating or cooling equipment, or any device that may cause uncontrolled air movement to minimize disturbance of the vapor level. If the degreaser must be placed in such an area, install baffles on the windward side to divert drafts, enclose the degreaser, or where possible, redirect fans and vents that cause disruptive air currents.

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.
  • Use racks and baskets made from light-weight, open-mesh, nonporous material. Ensure that the baskets or racks are small enough to allow clearance from the walls of the degreaser to avoid MC vapor being pulled out during loading and unloading. When possible, use conveyorized degreasing equipment to minimize worker exposure to MC.

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

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. In cases where aqueous cleaning is not effective, some non-chlorinated solvents such as isopropyl alcohol and mineral sprits may work.

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 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.