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Volume: 24
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Article No.: 3713

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SAFETY SOLUTIONS: Methylene Chloride
A while back one of our readers asked a question about Methylene chloride. The reader was updating their safety program and realized that the methelene chloride in all of their solvent cements for acrylics had been lowered from 200ppm to 25ppm. I researched the Federal OSHA regulations and also the National Institute of Occupational Safety & Health (NIOSHA) and came up with the following information.

Physical and Chemical Properties

Methylene chloride is a colorless, volatile, nonflammable liquid with a penetrating, ether-like odor that is detectable at about 200 parts per million (ppm) in air.

Methylene Chloride: The OSHA standard for methylene chloride was promulgated January 10, 1997. It reduces the PEL (permissible exposure level) from 500 ppm to 25 ppm. An amendment to the final rule was published on September 22, 1998.

The National Institute of Occupational Safety & Health (NIOSH) estimates that 1 million workers are potentially exposed to methylene chloride during its manufacture and use; as a solvent, aerosol propellant or fumigant and as a blowing agent in flexible urethane foams.

In 1976, NIOSH published a document entitled "Criteria for a Recommended Standard .... Occupational Exposure to Methylene Chloride." In that document, NIOSH recommended a 10-hour time-weighted average (TWA) occupational exposure limit of 75 parts per million in order to prevent interference by methylene chloride with delivery of oxygen to tissues, and impairment in functions of the central nervous system (CNS). Since 1976, the carcinogenicity of methylene chloride has been documented in several studies of chronic effects in animals. On the basis of carcinogenic and tumorigenic responses in rats and mice, and in accordance with the Cancer Policy of the Occupational Safety and Health Administration NIOSH recommends that Methylene chloride be regarded as a "potential occupational carcinogen." Although the potential for methylene chloride-induced cancer in humans has not been determined, the probability of a population of exposed workers developing cancer could be decreased by reducing exposure. Therefore, NIOSH recommends that occupational exposure to methylene chloride be controlled to the lowest feasible limit.

It is also recommended that producers and users of methylene chloride disseminate this information to their workers and customers, that professional and trade associations and unions inform their members of the potential hazards of working with methylene chloride, and that appropriate engineering controls and work practices are used to reduce the exposure of workers to the lowest feasible extent.

Data obtained by the National Toxicology Program from studies with methylene chloride using rats demonstrate exposure and dose-related increases in benign mammary tumors in males and females, respectively, and exposure-related malignant tumors of the lung and liver in male and female mice. These data in conjunction with the data obtained by the Halogenated Solvents Industry Alliance are sufficient to classify methylene chloride as an OSHA Category I potential carcinogen.

Because methylene chloride has been shown to induce increased numbers of benign and malignant neoplasms in rats and mice, it meets the criteria provided in the OSHA Cancer Policy for classifying a substance as a potential occupational carcinogen; therefore, NIOSH recommends that methylene chloride be considered a potential human carcinogen in the workplace.

The excess risk of cancer to workers exposed to specific airborne concentrations of methylene chloride has not yet been determined, but the probability of developing such an adverse effect would be decreased by reducing exposure. As prudent public health policy, employers should voluntarily assess the conditions under which workers may be exposed to methylene chloride and take all reasonable precautions to reduce exposures to the lowest feasible limit.

Guidelines for Minimizing Worker Exposure to Methylene Chloride
NIOSH recommends that employers, workers and health care professionals take the following actions to reduce the long-term risk of cancer and the possible risk of adverse effects on the cardiovascular system as a result of methylene chloride exposure.

1. Employers should:
a. Control worker exposure to the lowest feasible limit through effective engineering controls, good work practices and proper maintenance procedures.

b. Provide appropriate exhaust ventilation or control exposure by enclosed processes.

c. Provide isolation of workers by the use of remote control rooms and utilization of automated equipment.

d. Provide appropriate personal protective clothing and equipment to minimize contact with the skin and eyes, and require workers to change clothing that has become contaminated with methylene chloride.

e. Provide clothing change rooms, showers and eating areas free from methylene chloride or other chemical exposure. Eating and smoking should not be permitted in areas where methylene chloride is manufactured, stored or used.

f. Provide suitable and effective respiratory protective equipment (Table 1); provide fit testing and training on the proper use of respirators and provide for regular maintenance, inspection and cleaning of respirators.

g. Provide routine personal air monitoring for workers potentially exposed to methylene chloride and inform them of the results of analysis. Monitoring for carbon monoxide (CO) should also be conducted.

h. Provide a medical monitoring program that will detect methylene chloride-induced health effects (Table 2). Provide physicians or other health care personnel with all toxicologic information, industrial hygiene sampling data, and a listing of protective devices or equipment the worker may be required to use when a potential for exposure to methylene chloride exists.

i. Conduct medical evaluations to determine the worker’s physical fitness for using respiratory protective equipment.

j. When possible, replace methylene chloride with a chemical that has been shown not to cause cancer or other adverse health effects in animals or in humans.

k. Provide a worker education program designed to inform the worker about the potential health risks from exposure to methylene chloride, the proper use of personal protective equipment or clothing, smoking cessation programs and proper work practice procedures. l. Provide all workers who are or who may be exposed to methylene chloride with a copy of this CIB pointing out the list of adverse symptoms and health effects associated with exposure to methylene chloride (Table 2).

2. Workers should:
a. Make appropriate use of personal protective equipment and respirators provided by the employer.

b. Avoid contact with methylene chloride and immediately change clothing that has become contaminated with the chemical.

c. Immediately and thoroughly wash with soap and water all areas of the body that come into contact with methylene chloride.

d. Report any health signs and symptoms of exposure to methylene chloride to the responsible health professional. If a private physician is used, see that the physician receives a copy of this CIB.

3. Physicians and other health care professionals should:
a. Be familiar with the signs and symptoms that are suggestive of exposure of workers to methylene chloride.

b. Maintain complete medical, chemical exposure and occupational history information for each worker.

c. Perform periodic medical examinations, giving particular attention to the respiratory, cardiovascular and nervous systems and to the liver, pancreas, blood and skin, as these are the primary targets of exposure to methylene chloride.

Table 1
Respirator selection for methylene chloride
Conditions of UseRecommended Respirator
For any condition requiring the use of respirators except as noted below Self-contained breathing apparatus equipped with full facepiece and operated in a pressure-demand or other positive pressure made or
  Supplied-air respirator with a full facepiece and operated in a pressure-demand or other positive pressure made in combination with an auxiliary self-contained breathing apparatus or other positive pressure mode
Firefighting situation Self-contained breathing apparatus with a full facepiece and operated in a pressure-demand or other positive pressure mode
Escape situations Any air purifying respirator equipped with a full facepiece (gas mask) and an organic vapor canister; or appropriate escape-type self contained breathing apparatus

Table 2
Signs and symptoms of methylene chloride exposure
Eye or skin irritation
Tingling or numbness of extremeties

Copies of this and other NIOSH documents are available from the National Institute for Occupational Safety and Health, 4676 Columbia Parkway, Cincinnati, OH 45226, 800-35-NIOSH, Fax: 513-533-8573.

For more information, click on the Author Biography link at the top of this page.

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