Washington Administrative Code › Title 296 - Labor and Industries, Department of › Chapter 296-62 - General occupational health standards › Part G - CARCINOGENS (SPECIFIC) › Section 296-62-07475 - Appendix B

Current through Register Vol. 24-14, July 15, 2024
Medical Surveillance for Methylene Chloride
I.Primary Route of Entry
				Inhalation.
II.Toxicology.
Methylene Chloride (MC) is primarily an inhalation hazard.
				  The principal acute hazardous effects are the depressant action on the central
				  nervous system, possible cardiac toxicity and possible liver toxicity. The
				  range of CNS effects are from decreased eye/hand coordination and decreased
				  performance in vigilance tasks to narcosis and even death of individuals
				  exposed at very high doses. Cardiac toxicity is due to the metabolism of MC to
				  carbon monoxide, and the effects of carbon monoxide on heart tissue. Carbon
				  monoxide displaces oxygen in the blood, decreases the oxygen available to heart
				  tissue, increasing the risk of damage to the heart, which may result in heart
				  attacks in susceptible individuals. Susceptible individuals include persons
				  with heart disease and those with risk factors for heart disease. Elevated
				  liver enzymes and irritation to the respiratory passages and eyes have also
				  been reported for both humans and experimental animals exposed to MC
				  vapors.
MC is metabolized to carbon monoxide and carbon dioxide via
				  two separate pathways. Through the first pathway, MC is metabolized to carbon
				  monoxide as an end-product via the P-450 mixed function oxidase pathway located
				  in the microsomal fraction of the cell. This biotransformation of MC to carbon
				  monoxide occurs through the process of microsomal oxidative dechlorination
				  which takes place primarily in the liver. The amount of conversion to carbon
				  monoxide is significant as measured by the concentration of carboxyhemoglobin,
				  up to 12% measured in the blood following occupational exposure of up to 610
				  ppm. Through the second pathway, MC is metabolized to carbon dioxide as an end
				  product (with formaldehyde and formic acid as metabolic intermediates) via the
				  glutathione dependent enzyme found in the cytosolic fraction of the liver cell.
				  Metabolites along this pathway are believed to be associated with the
				  carcinogenic activity of MC.
MC has been tested for carcinogenicity in several laboratory
				  rodents. These rodent studies indicate that there is clear evidence that MC is
				  carcinogenic to male and female mice and female rats. Based on epidemiologic
				  studies, OSHA has concluded that there is suggestive evidence of increased
				  cancer risk in MC-related worker populations. The epidemiological evidence is
				  consistent with the finding of excess cancer in the experimental animal
				  studies. NIOSH regards MC as a potential occupational carcinogen and the
				  International Agency for Research Cancer (IARC) classifies MC as an animal
				  carcinogen. OSHA considers MC as a suspected human carcinogen.
III.Medical Signs and Symptoms of
				Acute Exposure Skin exposure to liquid MC may cause irritation or skin burns.
				Liquid MC can also be irritating to the eyes. MC is also absorbed through the
				skin and may contribute to the MC exposure by inhalation. At high
				concentrations in air, MC may cause nausea, vomiting, light-headedness,
				numbness of the extremities, changes in blood enzyme levels, and breathing
				problems, leading to bronchitis and pulmonary edema, unconsciousness and even
				death.
At lower concentrations in air, MC may cause irritation to
				  the skin, eye, and respiratory tract and occasionally headache and nausea.
				  Perhaps the greatest problem from exposure to low concentrations of MC is the
				  CNS effects on coordination and alertness that may cause unsafe operations of
				  machinery and equipment, leading to self-injury or accidents. Low levels and
				  short duration exposures do not seem to produce permanent disability, but
				  chronic exposures to MC have been demonstrated to produce liver toxicity in
				  animals, and therefore, the evidence is suggestive for liver toxicity in humans
				  after chronic exposure. Chronic exposure to MC may also cause cancer.
IV.Surveillance and Preventive
				Considerations
As discussed above, MC is classified as a suspect or
				  potential human carcinogen. It is a central nervous system (CNS) depressant and
				  a skin, eye and respiratory tract irritant. At extremely high concentrations,
				  MC has caused liver damage in animals. MC principally affects the CNS, where it
				  acts as a narcotic. The observation of the symptoms characteristic of CNS
				  depression, along with a physical examination, provides the best detection of
				  early neurological disorders. Since exposure to MC also increases the
				  carboxyhemoglobin level in the blood, ambient carbon monoxide levels would have
				  an additive effect on that carboxyhemoglobin level. Based on such information,
				  a periodic post- shift carboxyhemoglobin test as an index of the presence of
				  carbon monoxide in the blood is recommended, but not required, for medical
				  surveillance.
Based on the animal evidence and three epidemiologic studies
				  previously mentioned, OSHA concludes that MC is a suspect human carcinogen. The
				  medical surveillance program is designed to observe exposed workers on a
				  regular basis. While the medical surveillance program cannot detect MC-induced
				  cancer at a preneoplastic stage, OSHA anticipates that, as in the past, early
				  detection and treatments of cancers leading to enhanced survival rates will
				  continue to evolve.
A.Medical and
				Occupational History:
The medical and occupational work history plays an important
				  role in the initial evaluation of workers exposed to MC. It is therefore
				  extremely important for the examining physician or other licensed health care
				  professional to evaluate the MC-exposed worker carefully and completely and to
				  focus the examination on MC's potentially associated health hazards. The
				  medical evaluation must include an annual detailed work and medical history
				  with special emphasis on cardiac history and neurological symptoms.
An important goal of the medical history is to elicit
				  information from the worker regarding potential signs or symptoms associated
				  with increased levels of carboxyhemoglobin due to the presence of carbon
				  monoxide in the blood. Physicians or other licensed health care professionals
				  should ensure that the smoking history of all MC exposed employees is known.
				  Exposure to MC may cause a significant increase in carboxyhemoglobin level in
				  all exposed persons. However, smokers as well as workers with anemia or heart
				  disease and those concurrently exposed to carbon monoxide are at especially
				  high risk of toxic effects because of an already reduced oxygen carrying
				  capacity of the blood.
A comprehensive or interim medical and work history should
				  also include occurrence of headache, dizziness, fatigue, chest pain, shortness
				  of breath, pain in the limbs, and irritation of the skin and eyes. In addition,
				  it is important for the physician or other licensed health care professional to
				  become familiar with the operating conditions in which exposure to MC is likely
				  to occur. The physician or other licensed health care professional also must
				  become familiar with the signs and symptoms that may indicate that a worker is
				  receiving otherwise unrecognized and exceptionally high exposure levels of
				  MC.
An example of a medical and work history that would satisfy
				  the requirement for a comprehensive or interim work history is represented by
				  the following:
The following is a list of recommended questions and issues
				  for the self-administered questionnaire for methylene chloride exposure.
Questionnaire For Methylene Chloride
				  Exposure
I.Demographic
				Information
1. Name
2. Social Security Number
3. Date
4. Date of Birth
5. Age
6. Present occupation
7. Sex
8. Race