This appendix answers commonly asked questions about the
hazards from exposure to methylene chloride. It also
describes approaches to controlling methylene chloride
exposure during the most common furniture stripping processes.
Although these approaches were developed and field tested by
the National Institute of Occupational Safety and Health, each
setting requires custom installation because of the different
air flow interferences at each site.
1. What is the Stripping Solution Base?
The most common active ingredient in paint removers is a
chemical called methylene chloride. Methylene chloride is
present in the paint remover to penetrate, blister, and
finally lift the old finish. Other chemicals in paint
removers work to accelerate the stripping process, to retard
evaporation, and to act as thickening agents. These other
ingredients may include: methanol, toluene, acetone, or
paraffin.1
2. Is Methylene Chloride Bad for Me?
Exposure to methylene chloride may cause short-term health
effects or long-term health effects.
Short-Term (Acute) Health Effects
Exposure to high levels of paint removers over short periods
of time can cause irritation to the skin, eyes, mucous
membranes, and respiratory tracts. Other symptoms of high
exposure are dizziness, headache, and lack of coordination. The occurrence of any of these symptoms indicates that you are
being exposed to high levels of methylene chloride. At the
onset of any of these symptoms, you should leave the work
area, get some fresh air, and determine why the levels were
high.
A portion of inhaled methylene chloride is converted by the
body to carbon monoxide, which can lower the blood's ability
to carry oxygen. When the solvent is used properly, however,
the levels of carbon monoxide should not be hazardous. Individuals with cardiovascular or pulmonary health problems
should check with their physician before using the paint
stripper. Individuals experiencing severe symptoms such as
shortness of breath or chest pains should obtain proper
medical care immediately.1
Long-Term (Chronic) Health Effects
Methylene chloride has been shown to cause cancer in certain
laboratory animal tests. The available human studies do not
provide the necessary information to determine whether
methylene chloride causes cancer in humans. However, as a
result of the animal studies, methylene chloride is considered
a potential occupational carcinogen. There is also
considerable indirect evidence to suggest that workers exposed
to methylene chloride may be at an increased risk of
developing ischemic heart disease. Therefore, it is prudent
to minimize exposure to solvent vapors.3
3. What does the Methylene Chloride Standard Require?
On January 10, 1997, the Occupational Safety and Health
Administration published a new regulation for methylene
chloride. The standard establishes an eight-hour
time-weighted average exposure limit of 25 parts per million
(ppm), as well as a short-term exposure limit of 125 ppm
determined from a 15 minute sampling period. That is a
reduction from the current WISHA limit of 100 ppm. The
standard also sets a 12.5 ppm action level (a level that would
trigger periodic exposure monitoring and medical surveillance
provisions).2 WISHA adopted an identical standard on [date].
The National Institute for Occupational Safety and Health
recommends that methylene chloride be regarded as a "potential
occupational carcinogen." NIOSH further recommends that
occupational exposure to methylene chloride be controlled to
the lowest feasible limit. This recommendation was based on
the observation of cancers and tumors in both rats and mice
exposed to methylene chloride in air.5
4. How Can I Be Exposed to Methylene Chloride while Stripping
Furniture?
Methylene chloride can be inhaled when vapors are in the air. Inhalation of the methylene chloride vapors is generally the
most important source of exposure. Methylene chloride
evaporates quicker than most chemicals. The odor threshold of
methylene chloride is 300 ppm.6 Therefore, once you smell
methylene chloride, you are being over-exposed. Pouring,
moving, or stirring the chemical will increase the rate of
evaporation.
Methylene chloride can be absorbed through the skin either by
directly touching the chemical or through your gloves. Methylene chloride can be swallowed if it gets on your hands,
clothes, or beard, or if food or drinks become contaminated.
5. How Can Breathing Exposures be Reduced?
Install a Local Exhaust Ventilation System
Local exhaust ventilation can be used to control exposures. Local exhaust ventilation systems capture contaminated air
from the source before it spreads into the workers' breathing
zone.7 If engineering controls are not effective, only a
self-contained breathing apparatus equipped with a full face
piece and operated in a positive-pressure mode or a
supplied-air respirator affords the level of protection. Air-purifying respirators such as gas masks with organic vapor
canisters can only be used for escape situations.8 These gas
masks are not suitable for normal work situations because
methylene chloride is poorly absorbed by the canister
filtering material.
A local exhaust system consists of the following: a hood, a
fan, ductwork, and a replacement air system.9,10,11 Two processes
are commonly used in furniture stripping: Flow-over and dip
tanks. For flow-over systems there are two common local
exhaust controls for methylene chloride - a slot hood and a
down draft hood. A slot hood of different design is most
often used for dip tanks. (See Figures 1, 2, and 3.)
The hood is made of sheet metal and connected to the tank. All designs require a centrifugal fan to exhaust the fumes,
ductwork connecting the hood and the fan, and a replacement
air system to bring conditioned air into the building to
replace the air exhausted.
In constructing or designing a slot or down draft hood, use
the following data:
FIGURE 1 -- SLOT HOOD
FIGURE 2 -- DOWNDRAFT HOOD
FIGURE 3 -- SLOT HOOD FOR DIP TANK
Safe Work Practices
Workers can lower exposures by decreasing their access to the
methylene chloride.12
1) Turn on dip tank control system several minutes before
entering the stripping area.
2) Avoid unnecessary transferring or moving of the stripping
solution.
3) Keep face out of the air stream between the
solution-covered furniture and the exhaust system.
4) Keep face out of vapor zone above the stripping solution
and the dip tank.
5) Retrieve dropped items with a long handled tool.
6) Keep the solution-recycling system off when not in use. Cover reservoir for recycling system.
7) Cover dip tank when not in use.
8) Provide adequate ventilation for rinse area.
How Can Skin Exposures Be Reduced?
Skin exposures can be reduced by wearing gloves whenever you
are in contact with the stripping solution.13
1) Two gloves should be worn. The inner glove should be made
from polyethylene/ethylene vinyl alcohol (e.g., Silver
Shield¦, or 4H¦). This material, however, does not provide
good physical resistance against tears, so an outer glove made
from nitrile or neoprene should be worn.
2) Shoulder-length gloves will be more protective.
3) Change gloves before the break-through time occurs. Rotate
several pairs of gloves throughout the day. Let the gloves
dry in a warm well ventilated area at least over night before
reuse.
4) Keep gloves clean by rinsing often. Keep gloves in good
condition. Inspect the gloves before use for pin-holes,
cracks, thin spots, and stiffer than normal or sticky
surfaces.
5) Wear a face shield or goggles to protect face and eyes.
6. What Other Problems Can Occur?
Stripping Solution Temperature
Most manufacturers of stripping solution recommend controlling
the solution to a temperature of 70°F. This temperature is
required for the wax in the solution to form a vapor barrier
on top of the solution to keep the solution from evaporating
too quickly. If the temperature is too high, the wax will not
form the vapor barrier. If it is too cold, the wax will
solidify and separate from the solvent causing increased
evaporation. Use a belt heater to heat the solution to the
correct temperature. Call your solution manufacturer for the
correct temperature for your solution.14
Make-Up Air
Air will enter a building in an amount to equal the amount of
air exhausted whether or not provision is made for this
replacement. If a local exhaust system is added a make-up or
replacement air system must be added to replace the air
removed. Without a replacement air system, air will enter the
building through cracks causing uncontrollable eddy currents. If the building perimeter is tightly sealed, it will prevent
the air from entering and severely decrease the amount
exhausted from the ventilation system. This will cause the
building to be under negative pressure and decrease the
performance of the exhaust system.15
Dilution Ventilation
With general or dilution ventilation, uncontaminated air is
moved through the workroom by means of fans or open windows,
which dilutes the pollutants in the air. Dilution ventilation
does not provide effective protection to other workers and
does not confine the methylene chloride vapors to one area.16
Phosgene Poisoning from Use of Kerosene Heaters
Do not use kerosene heaters or other open flame heaters while
stripping furniture. Use of kerosene heaters in connection
with methylene chloride can create lethal or dangerous
concentrations of phosgene. Methylene chloride vapor is mixed
with the air used for the combustion of kerosene in kerosene
stoves. The vapor thus passes through the flames, coming into
close contact with carbon monoxide at high temperatures. Any
chlorine formed by decomposition may, under these conditions,
react with carbon monoxide and form phosgene.17
REFERENCES
1Halogenated Solvents Industry Alliance and Consumer Product
Safety Commission [1990]. Stripping Paint from Wood (Pamphlet
for consumers on how to strip furniture and precautions to
take). Washington DC: Consumer Product Safety Commission.
2Ibid.
3NIOSH [1992]. NIOSH Testimony on Occupational Safety and
Health Administration's proposed rule on occupational exposure
to methylene chloride, September 21, 1992, OSHA Docket No.
H-71. NIOSH policy statements. Cincinnati, OH: U.S.
Department of Health and Human Services, Public Health
Service, Centers for Disease Control, National Institute for
Occupational Safety and Health.
456 Fed. Reg. 57036 [1991]. Occupational Safety and Health
Administration: Proposed rule on occupational exposure to
methylene chloride.
5NIOSH [1992].
6Kirk, R.E. and P.F. Othmer, Eds. [1978]. Encyclopedia of
Chemical Technology, 3rd Ed., Vol. 5:690. New York: John
Wiley & Sons, Inc.
7ACGIH [1988]. Industrial Ventilation: A Manual of
Recommended Practice. 20th Ed. Cincinnati, OH: American
Conference of Governmental Industrial Hygienists.
8NIOSH [1992].
9Fairfield, C.L. and A.A. Beasley [1991]. In-depth Survey
Report at the Association for Retarded Citizens, Meadowlands,
PA. The Control of Methylene Chloride During Furniture
Stripping. Cincinnati, OH: U.S. Department of Health and
Human Services, Public Health Service, Centers for Disease
Control, National Institute for Occupational Safety and
Health.
10Fairfield, C.L. [1991]. In-depth Survey Report at the J.M.
Murray Center, Cortland, NY. The Control of Methylene
Chloride During Furniture Stripping. Cincinnati, OH: U.S.
Department of Health and Human Services, Publish Health
Service, Centers for Disease Control, National Institute for
Occupational Safety and Health.
11Hall, R.M., K.F. Martinez, and P.A. Jensen [1992]. In-depth
Survey Report at Tri-County Furniture Stripping and
Refinishing, Cincinnati, OH. The Control of Methylene
Chloride During Furniture Stripping. Cincinnati, OH: U.S.
Department of Health and Human Services, Public Health
Service, Centers for Disease Control, National Institute for
Occupational Safety and Health.
12Fairfield, C.L. and A.A. Beasley [1991]. In-depth Survey
Report at the Association for Retarded Citizens, Meadowlands,
PA. The Control of Methylene Chloride During Furniture
Stripping. Cincinnati, OH: U.S. Department of Health and
Human Service, Centers for Disease Control, National Institute
for Occupational Safety and Health.
13Roder, M. [1991]. Memorandum of March 11, 1991 from Michael
Roder of the Division of Safety Research to Cheryl L.
Fairfield of the Division of Physical Sciences and
Engineering, National Institute for Occupational Safety and
Health, Centers for Disease Control, Public Health Service,
U.S. Department of Health and Human Services.
17Gerritsen, W.B. and C.H. Buschmann [1960]. Phosgene
Poisoning Caused by the Use of Chemical Paint Removers
containing Methylene Chloride in Ill-Ventilated Rooms Heated
by Kerosene Stoves. British Journal of Industrial Medicine
17:187.
