Methylene Chloride Facts No. 5
Suggested Engineering Controls and Work Practices for Construction Sites

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 construction companies use products that contain MC. Exposure often happens when workers are stripping paint or other coatings, applying foam, painting with epoxy paint, cleaning equipment with solvents, and spraying adhesives. Workers are more likely to be exposed to high levels of MC when working in small, enclosed spaces that are not well ventilated. The following describes some engineering controls and work practices that you may find helpful in reducing worker exposures to MC at your site.

Monitoring

Employers must monitor worker exposures to MC to determine whether engineering controls or work practices 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. Note: Initial monitoring is not necessary if employees are exposed to MC for fewer than 30 days per year, and the employer uses direct-reading instruments giving immediate results and providing sufficient information to determine the necessary control measures to reduce exposures to acceptable levels.

For additional information on monitoring for MC, see OSHA Methylene Chloride Facts No. 01.

Ventilation Systems

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:

  • Where possible, use MC products outdoors.
  • Use a portable local exhaust ventilation (LEV) unit when working with MC indoors or in areas with limited ventilation for long periods of time.
  • Be sure to use a replacement air system, or else the LEV will not work properly.
  • Turn on portable LEV units several minutes before you enter the work area.
  • Run the LEV at a high enough airflow to reduce exposures below the 8-hour time-weighted average (TWA) permissible exposure limit (PEL), and 15-minute short-term exposure limit (STEL).

After you install a new ventilation system, you must monitor worker exposures again to determine whether the system is effective. 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 where exposures are not very high.

  • Turn on general ventilation at least an hour before work begins or leave it on overnight.

Keep MC Vapors Contained

  • Store and transport MC products only in approved safety containers.
  • Properly label all MC product containers to indicate their contents, hazards, and proper use, storage, and disposal. Read these labels and follow the directions.
  • Keep MC product containers closed tightly when not in use.
  • Avoid unnecessary transfer or movement of MC products.

Avoid Breathing MC Vapors

  • Avoid breathing the air directly above areas covered with MC. Do not lean over an area covered with MC.
  • Do not work or stand between MC-covered areas and the exhaust system.
  • Do not rely on the odor of MC to warn you of over-exposure. People cannot smell MC until vapor concentrations are above 300 ppm, which is 12 times higher than the 8-hour TWA PEL of 25 ppm. Also, your sense of smell can quickly get used to the odor of MC so that you stop noticing it.
  • If you become dizzy, light-headed, or have other symptoms of MC exposure, go immediately to an area with fresh air.

Avoid Direct Skin Contact with MC

  • Wear two pairs of gloves when using stripping solution. The inner glove should be made of polyethylene (PE)/ethylene vinyl alcohol (EVOH), PE, or laminate to prevent MC penetration. The outer glove should be made of nitrile or neoprene to protect against puncture or rips. [Note: Because MC can readily penetrate nitrile and neoprene, wearing just the outer glove will not protect your skin from MC exposure.]
    • Wear shoulder length gloves, or the longest gloves possible.
    • Before use, inspect gloves for pin-holes, cracks, thin spots, softening, swelling, and stiff or sticky surfaces.
    • Change gloves frequently, before breakthrough occurs.
    • Rotate several pairs of gloves throughout the day.
    • Let gloves dry in a warm, well-ventilated area at least overnight before reuse.
  • Wear rubber aprons and boots or shoe covers to prevent MC from getting on your clothes, which results in prolonged skin contact with MC.
  • Wear a face shield or goggles to protect your face and eyes.
  • Use the washing facilities in your work area to wash off any MC from your hands and face.
  • Use lots of soap or mild detergent and water to clean grease, oil, dirt, or anything else off your skin. Do not use MC or other organic solvents to clean your skin.

Minimize the Chance of Spills and Leaks

  • Develop and follow procedures for containing MC spills or leaks.
  • Frequently inspect MC product containers for cracks or other possible sources of leaks.
  • Clean up all spills and leaks as quickly as possible.
  • Place rags, waste, paper towels, or absorbent used to clean spills in a closed container (preferably a non-aluminum, all-metal safety container) immediately after use.
  • Make sure that leaks are repaired and spills cleaned up by employees who are trained in proper cleanup methods. These employees should wear appropriate personal protective equipment (PPE).

Take Extra Precautions in Low and Confined Spaces

MC vapors are heavier than air, so they tend to move to low, unventilated spaces.

  • Do not enter or lean into a low-lying confined area until it has been completely aired out and tested. Wear proper PPE and follow the appropriate confined space entry procedures outlined in OSHA's Permit Required Confined Spaces standard (29 CFR 1910.146).
  • Use a long-handled tool to pick up items that you drop in areas where MC is being used.

Take Personal Precautions

  • After working with MC, always wash your face and hands before eating.
  • Never eat in the work area or your food and drink could become contaminated with MC.
  • Avoid drinking alcohol before or after being exposed to MC. Alcohol can lower the amount of MC needed to cause health problems.
  • Be alert when working with MC. Avoid situations that might result in overexposure.
  • If your clothes become soaked with MC, remove them and take a shower. Do not put your clothes back on until they are thoroughly clean and dry.

Substitutes

Using products that do not contain MC is a good way to reduce worker exposure to MC. Many adhesives, solvents, foams, and paints no longer use MC as a propellant and are widely available (check labels). In addition, a number of paint strippers that do not contain MC are currently available.

  • n-Methyl-pyrrolidone (NMP) can remove clear and pigmented nitrocellulose lacquers, conventional varnish, and all types of water-based 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.

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, workers must wear supplied-air respirators. Respirators are the least preferred method of controlling employee exposure. 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.