Methylene Chloride Facts No. 11
Suggested Work Practices 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 health disease (e.g., chest pains, angina) worse.

Some workers at facilities that perform open-top and/or conveyorized vapor degreasing operations are at risk of being exposed to high levels of MC. In many of these facilities, improving work practices and housekeeping procedures can greatly reduce exposure to MC. The following suggested practices may help you reduce your workplace exposures.

Minimize MC Vapor Losses from Degreasing Tanks

  • Keep degreasing tanks covered when not in use.
  • Start water flow to the tank's cooling coils before applying heat to the MC solution. Likewise, turn-off the heat before the cooling coils during shutdown.
  • Continuously monitor and control the amount of heat supplied to the MC solution. Too much heat will result in excessive vapor concentrations.
  • When spraying parts, keep the nozzle as low as possible in the tank. This will help keep MC vapors in the degreaser and out of the work area.
  • Maintain the correct pressure when spraying parts with MC to avoid splattering.
  • Do not overload the racks. Overloading causes a big drop in the vapor capacity of the vapor zone which forces MC vapors out of the degreaser.
  • Do not arrange parts in the rack so that liquids or vapors can be easily trapped in and between parts.
  • Never clean absorbent materials in the degreaser (EPA's maximum achievable control technology (MACT) standard does not allow it).
  • Make sure the cleaning cycle is long enough for the parts to reach vapor temperature. If parts do not reach vapor temperature, they will still be covered with MC when unloaded from the tank. Do not remove wet parts that are covered with MC from the degreasing tank.
  • Do not raise or lower the rack at a rate faster than 11 feet per minute, or the maximum rate recommended by the manufacturer, whichever is slower. Quick rack movement increases MC drag out which is a major source of MC exposure.
  • Carefully remove parts after degreasing to prevent them from swinging back and forth (rocking). Rocking increases drag out.
  • If tilting the rack is necessary to drain MC from parts, do it as low as possible in the vapor zone and always below the condensing coils.

Avoid Breathing MC Vapors

  • Turn on any ventilation systems at least an hour before work begins or leave it on overnight.
  • Avoid breathing air directly above the degreasing tank. Do not lean over the tank when working. Use long-handled tools for additional spraying.
  • Only stand near the degreasing tank when you have to load and unload the racks (even if the tank is covered).
  • Do not work or stand between the degreasing tank or other sources of MC 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 time-weighted average permissible exposure limit 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.

Keep MC Vapors Contained

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

Minimize the Chance of Spills and Leaks

  • Develop and follow procedures for containing MC spills or leaks.
  • Frequently inspect the degreasing tank, piping equipment, and MC containers for cracks, loose parts, and 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 such as tanks and maintenance pits. This is of particular concern since degreasing tanks must be cleaned regularly.

  • Do not enter the degreasing tank or any other 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 supplied-air respirator when cleaning the degreasing tank.
  • Use a long-handled tool to pick up items that you drop into a tank, confined space, or low-lying area.

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.

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 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.