I. Primary Route of Entry
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
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
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
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
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
2. Social Security Number
4. Date of Birth
6. Present occupation
II. Occupational History
1. Have you ever worked with methylene chloride, dichloromethane,
methylene dichloride, or CH(2)Cl(2) (all are different names
for the same chemical)? Please list which on the occupational history
form if you have not already.
2. If you have worked in any of the following industries and have
not listed them on the occupational history form, please do so.
Polyurethane foam manufacturing
Chemical manufacturing or formulation
Any industry in which you used solvents to clean and degrease
equipment or parts
Construction, especially painting and refinishing
Any industry in which you used aerosol adhesives
3. If you have not listed hobbies or household projects on the
occupational history form, especially furniture refinishing, spray
painting, or paint stripping, please do so.
III. Medical History
1. Do you consider yourself to be in good health? If no, state
2. Do you or have you ever had:
a. Persistent thirst
b. Frequent urination (three times or more at night)
c. Dermatitis or irritated skin
d. Non-healing wounds
3. What prescription or non-prescription medications do you take,
and for what reasons?
4. Are you allergic to any medications, and what type of reaction
do you have?
1. Do you have or have you ever had any chest illnesses or
2. Do you have or have you ever had any of the following:
c. Shortness of breath
3. Have you ever had an abnormal chest X-ray? If so, when, where,
and what were the findings?
4. Have you ever had difficulty using a respirator or breathing
5. Do any chest or lung diseases run in your family? Explain.
6. Have you ever smoked cigarettes, cigars, or a pipe? Age
7. Do you now smoke?
8. If you have stopped smoking completely, how old were you when
9. On the average of the entire time you smoked, how many packs of
cigarettes, cigars, or bowls of tobacco did you smoke per day?
1. Have you ever been diagnosed with any of the following: Which of
the following apply to you now or did apply to you at some time in
the past, even if the problem is controlled by medication? Please
explain any yes answers (i.e., when problem was diagnosed, length of
time on medication).
a. High cholesterol or triglyceride level
b. Hypertension (high blood pressure)
d. Family history of heart attack, stroke, or blocked arteries
2. Have you ever had chest pain? If so, answer the next five
a. What was the quality of the pain (i.e., crushing, stabbing,
b. Did the pain go anywhere (i.e., into jaw, left arm)?
c. What brought the pain out?
d. How long did it last?
e. What made the pain go away?
3. Have you ever had heart disease, a heart attack, stroke,
aneurysm, or blocked arteries anywhere in you body? Explain (when,
4. Have you ever had bypass surgery for blocked arteries in your
heart or anywhere else? Explain.
5. Have you ever had any other procedures done to open up a blocked
artery (balloon angioplasty, carotid endarterectomy, clot-dissolving
6. Do you have or have you ever had (explain each):
a. Heart murmur
b. Irregular heartbeat
c. Shortness of breath while lying flat
d. Congestive heart failure
e. Ankle swelling
f. Recurrent pain anywhere below the waist while walking
7. Have you ever had an electrocardiogram (EKG)? When?
8. Have you ever had an abnormal EKG? If so, when, where, and what
were the findings?
9. Do any heart diseases, high blood pressure, diabetes, high
cholesterol, or high triglycerides run in your family? Explain.
D. Hepatobiliary and Pancreas
1. Do you now or have you ever drunk alcoholic beverages? Age
started: ________ Age stopped: ________.
2. Average numbers per week:
a. Beers: ________, ounces in usual container:
b. Glasses of wine: ________, ounces per glass:
c. Drinks: ________, ounces in usual container:
3. Do you have or have you ever had (explain each):
a. Hepatitis (infectious, autoimmune, drug-induced,
c. Elevated liver enzymes or elevated bilirubin
d. Liver disease or cancer
E. Central Nervous System
1. Do you or have you ever had (explain each):
d. Loss of consciousness
e. Garbled speech
f. Lack of balance
g. Mental/psychiatric illness
1. Do you have, or have you ever had (explain each):
b. Sickle cell disease or trait
c. Glucose-6-phosphate dehydrogenase deficiency
d. Bleeding tendency disorder
2. If not already mentioned previously, have you ever had a
reaction to sulfa drugs or to drugs used to prevent or treat malaria?
What was the drug? Describe the reaction.
B. Physical Examination
The complete physical examination, when coupled with the medical
and occupational history, assists the physician or other licensed
health care professional in detecting pre-existing conditions that
might place the employee at increased risk, and establishes a
baseline for future health monitoring. These examinations should
1. Clinical impressions of the nervous system, cardiovascular
function and pulmonary function, with additional tests conducted
where indicated or determined by the examining physician or other
licensed health care professional to be necessary.
2. An evaluation of the advisability of the worker using a
respirator, because the use of certain respirators places an
additional burden on the cardiopulmonary system. It is necessary for
the attending physician or other licensed health care professional to
evaluate the cardiopulmonary function of these workers, in order to
inform the employer in a written medical opinion of the worker's
ability or fitness to work in an area requiring the use of certain
types of respiratory protective equipment. The presence of facial
hair or scars that might interfere with the worker's ability to wear
certain types of respirators should also be noted during the
examination and in the written medical opinion.
Because of the importance of lung function to workers required to
wear certain types of respirators to protect themselves from MC
exposure, these workers must receive an assessment of pulmonary
function before they begin to wear a negative pressure respirator and
at least annually thereafter. The recommended pulmonary function
tests include measurement of the employee's forced vital capacity
(FVC), forced expiratory volume at one second (FEV(1)), as well as
calculation of the ratios of FEV(1) to FVC, and the ratios of
measured FVC and measured FEV(1) to expected respective values
corrected for variation due to age, sex, race, and height. Pulmonary
function evaluation must be conducted by a physician or other
licensed health care professional experienced in pulmonary function
The following is a summary of the elements of a physical exam which
would fulfill the requirements under the MC standard:
I. Skin and appendages
1. Irritated or broken skin
3. Clubbing cyanosis, edema
4. Capillary refill time
1. Facial deformities
3. Hair growth
1. Scleral icterus
2. Corneal arcus
3. Pupillary size and response
4. Fundoscopic exam
1. Standard exam
1. Standard exam
2. Jugular vein distension
3. Peripheral pulses
1. Liver span
VII. Nervous System
1. Complete standard neurologic exam
1. Hemoglobin and hematocrit
2. Alanine aminotransferase (ALT, SGPT)
3. Post-shift carboxyhemoglobin
1. Pulmonary function testing
An evaluation of the oxygen carrying capacity of the blood of
employees (for example by measured red blood cell volume) is
considered useful, especially for workers acutely exposed to MC.
It is also recommended, but not required, that end of shift
carboxyhemoglobin levels be determined periodically, and any level
above 3% for non-smokers and above 10% for smokers should prompt an
investigation of the worker and his workplace. This test is
recommended because MC is metabolized to CO, which combines strongly
with hemoglobin, resulting in a reduced capacity of the blood to
transport oxygen in the body. This is of particular concern for
cigarette smokers because they already have a diminished hemoglobin
capacity due to the presence of CO in cigarette smoke.
C. Additional Examinations and Referrals
1. Examination by a Specialist
When a worker examination reveals unexplained symptoms or signs
(i.e. in the physical examination or in the laboratory tests),
follow-up medical examinations are necessary to assure that MC
exposure is not adversely affecting the worker's health. When the
examining physician or other licensed health care professional finds
it necessary, additional tests should be included to determine the
nature of the medical problem and the underlying cause. Where
relevant, the worker should be sent to a specialist for further
testing and treatment as deemed necessary.
The final rule requires additional investigations to be covered and
it also permits physicians or other licensed health care
professionals to add appropriate or necessary tests to improve the
diagnosis of disease should such tests become available in the
The examination of workers exposed to MC in an emergency should be
directed at the organ systems most likely to be affected. If the
worker has received a severe acute exposure, hospitalization may be
required to assure proper medical intervention. It is not possible to
precisely define "severe," but the physician or other licensed
health care professional's judgement should not merely rest on
hospitalization. If the worker has suffered significant conjunctival,
oral, or nasal irritation, respiratory distress, or discomfort, the
physician or other licensed health care professional should instigate
appropriate follow-up procedures. These include attention to the
eyes, lungs and the neurological system. The frequency of follow-up
examinations should be determined by the attending physician or other
licensed health care professional. This testing permits the early
identification essential to proper medical management of such
D. Employer Obligations
The employer is required to provide the responsible physician or
other licensed health care professional and any specialists involved
in a diagnosis with the following information: a copy of the MC
standard including relevant appendices, a description of the affected
employee's duties as they relate to his or her exposure to MC; an
estimate of the employee's exposure including duration (e.g.,
15hr/wk, three 8-hour shifts/wk, full time); a description of any
personal protective equipment used by the employee, including
respirators; and the results of any previous medical determinations
for the affected employee related to MC exposure to the extent that
this information is within the employer's control.
E. Physicians' or Other Licensed Health Care Professionals' Obligations
The standard requires the employer to ensure that the physician or
other licensed health care professional provides a written statement
to the employee and the employer. This statement should contain the
physician's or licensed health care professional's opinion as to
whether the employee has any medical condition placing him or her at
increased risk of impaired health from exposure to MC or use of
respirators, as appropriate. The physician or other licensed health
care professional should also state his or her opinion regarding any
restrictions that should be placed on the employee's exposure to MC
or upon the use of protective clothing or equipment such as
respirators. If the employee wears a respirator as a result of his or
her exposure to MC, the physician or other licensed health care
professional's opinion should also contain a statement regarding the
suitability of the employee to wear the type of respirator assigned.
Furthermore, the employee should be informed by the physician or
other licensed health care professional about the cancer risk of MC
and about risk factors for heart disease, and the potential for
exacerbation of underlying heart disease by exposure to MC through
its metabolism to carbon monoxide. Finally, the physician or other
licensed health care professional should inform the employer that the
employee has been told the results of the medical examination and of
any medical conditions which require further explanation or
treatment. This written opinion must not contain any information on
specific findings or diagnosis unrelated to employee's occupational
The purpose in requiring the examining physician or other licensed
health care professional to supply the employer with a written
opinion is to provide the employer with a medical basis to assist the
employer in placing employees initially, in assuring that their
health is not being impaired by exposure to MC, and to assess the
employee's ability to use any required protective equipment.
[62 FR 1493, Jan. 10, 1997]