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Methylene Chloride Facts No. 11
Suggested Work Practices for Vapor Degreasing Operations
Occupational Safety and Health Administration (1998)
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,
just 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
Avoid Breathing MC Vapors
- 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
- 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 Direct Skin Contact with MC
- Turn on any ventilation systems at least an hour before work begins or leave it on
- 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
- 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.
Keep MC Vapors Contained
- 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
- 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
- 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.
Take Extra Precautions in Low and Confined Spaces
- 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
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.
Take Personal Precautions
- 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
- 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.
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.
Employers with less than 20 employees have until:
Employers with more than 20 employees have until:
- February 4, 1998 to implement paragraph (d) (Initial Monitoring).
- April 10, 2000 to implement paragraph (f) (Engineering Controls).
- April 10, 1998 to implement all other provisions.
- September 7, 1997 to implement paragraph (d) (Initial Monitoring).
- April 10, 1998 to implement paragraph (f) (Engineering Controls).
- December 21, 1997 to implement all other provisions.
For more information concerning consultation assistance, contact the
nearest OSHA office (look under state listings for the Department of Labor),
refer to the listings on
OSHA's web site,
or contact OSHA's Office of Information at (202) 219-8151.