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Methylene Chloride Facts No. 6
Suggested Engineering Controls for
Flexible Polyurethane Foam Manufacturers
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.
Many facilities that manufacture flexible polyurethane foam (p-foam) use MC as a
blowing agent to make soft foam. Most 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. The revised standard published on
September 22, 1998 (FR
63; 50712-50732) contains additional STEL monitoring requirements for those specific
industries taking advantage of the extended compliance dates. 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.
Tunnel Controls
Worker exposures to MC are highest near the tunnel where p-foam is made. MC vapors come
from the front end of the tunnel where the raw materials are poured and mixed, from the
bottom end of the tunnel where the foam is cut, and from leaks and openings in the tunnel.
Most tunnels have local exhaust ventilation (LEV) units.
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.
If monitoring results indicate that worker exposures to MC are above established limits
when working near the tunnel, and new or improved controls are necessary, consider using
one or more of the following control options:
- Install an LEV unit in the tunnel. Note: A make-up air system is
required to ensure the proper operation of the LEV.
- Increase the exhaust capacity of the tunnel's ventilation system.
- Decrease the distance between the p-foam and the exhaust system. This will allow the LEV
to remove more MC. You can lower the tunnel's ceiling or change the location of the
exhaust inlets (e.g., use a slot exhaust at the inner perimeter of the tunnel).
- Use a tunnel with two open ends that allow make-up air to exhaust MC vapors.
- Use disposable tunnel liners so that workers do not need to use MC to clean tunnel
walls.
- Do not use aluminum in any equipment used to handle, store, or process MC. MC corrodes
aluminum. If aluminum parts fail, spills will occur.
- If MC is used to flush the mixing head and delivery hoses, do this in a closed loop to
the MC container so the solvent can be collected and reused rather than being allowed to
evaporate into the workplace. Mixing head parts can also be soaked in MC in closed
containers. If this is not feasible, leave the tunnel fan on and conduct cleaning
operations in the tunnel.
Saw Operator Controls
The saw operator is often exposed to high levels of MC, so additional controls may be
necessary to protect these workers. If monitoring results indicate that saw operator
exposures to MC are above established limits, and new or improved controls are necessary,
consider using one or more of the following control options:
- Mount a slot exhaust system on the guide tracks of the saw. Use a flexible hose to
connect this system to the exhaust conduit. This will allow the exhaust system to move
with the saw as the saw cuts the foam.
- Provide the saw operator with a fresh air island. The fresh air island brings fresh air
in from above the worker, blows it past the worker's breathing area, and exhausts it
through the floor. The air velocity of the fresh air island must be greater than velocity
of the air inside the tunnel for this strategy to work.
Cooling Area Control Options
As the foam cools, it releases MC. Most MC is released during the first few hours of
cooling. If monitoring results indicate that worker exposures to MC are above established
limits when working in or near the cooling area, and new or improved controls are
necessary, consider using one or more of the following control options:
- Allow p-foam to cool outside in canopies or open structures if possible to obtain
natural ventilation.
- Install a general ventilation system. Place the exhaust fans near the cooling p-foam.
[General ventilation does not confine MC vapors to one area, so it usually does not
protect workers as well as LEV.]
- Turn on general ventilation at least an hour before work begins or leave it on
overnight.
- Provide a ventilated, conditioned-air cab for the forklift and/or crane operator. A cab
provides continuous protection for these workers when they are in the tunnel area and the
cooling and storage area.
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 blowing agents other than MC is another way to reduce MC exposure.
- Acetone produces high quality soft foams and can be used instead of MC. Acetone is
extremely flammable, so be sure to take appropriate precautions.
- Some facilities use variable pressure when blowing foam (i.e., the foam is blown in a
vacuum). This eliminates the need to use auxiliary blowing agents such as MC.
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, 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 in p-foam manufacturing 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, 2000 to implement Respiratory Protection to achieve the 8-hour TWA PEL only.
- April 10, 1998 to implement all other provisions.
Employers in p-foam manufacturing with 20 - 99 employees have until:
- December 21, 1997 to implement paragraph (d) (Initial Monitoring).
- October 10, 1999 to implement paragraph (f) (Engineering Controls).
- October 10, 1999 to implement Respiratory Protection to achieve the 8-hour TWA PEL only.
- January 5, 1998 to implement all other provisions.
Employers in p-foam manufacturing with 100 or more employees have
until:
- September 7, 1997 to implement paragraph (d) (Initial Monitoring).
- October 10, 1999 to implement paragraph (f) (Engineering Controls).
- October 10, 1999 to implement Respiratory Protection to achieve the 8-hour TWA PEL only.
- 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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