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.
About 23,717 facilities that perform cold degreasing and other cold cleaning operations
use 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 or OSHA's Chemical Sampling Information which is
accessible through
OSHA's web site.
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.
Compliance Schedule
Employers with less 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.
Employers with more than 20 employees have until:
- 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.
Additional Resources
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.
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