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Methylene Chloride Facts No. 10
Suggested Engineering Controls for Vapor Degreasing Operations
Occupational Safety and Health Administration (1998)
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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 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:
- 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.
- Providemeans 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.
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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