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Workplace Air Monitoring: Exposure
Evaluation and Assessment
It is the policy of MIT to provide a safe working
environment for everyone working with chemicals either in the laboratory
or in shops or other facilities. The federal agency responsible
for setting safe levels of airborne exposure to chemicals is the
Occupational Safety and Health Administration (OSHA). Through government
standards 29 CFR 1910.1000 through 1052, OSHA sets safe levels of
airborne exposure to about 750 chemicals. For chemicals that are
rapidly or acutely toxic, OSHA sets 15 minute Short Term Exposure
Limits (STELs). For chemicals that have chronic toxicity, OSHA establishes
8 hour Permissible Exposure Limits (PELs). An 8 hour PEL for a chemical
is set low enough so that exposure 8 hours a day, 5 days per week,
for a working life time will not cause injury to health.
Laboratory Air Monitoring
In the Laboratory Standard, OSHA mandates that all laboratories
develop and implement safe operating practices for their laboratories,
which include safe handling of chemicals and compliance with the
PELS. It is the responsibility of department principal investigators
and supervisors to train their employees to understand the hazards
of the chemicals that are used in their laboratories, the signs
and symptoms of exposure, and the PELs. The primary method used
to control exposure in laboratories is the chemical fume hood, which
can control exposures to sub-part per million (ppm) levels when
used properly. If there are questions about exposure levels, the
Industrial Hygiene Program can perform an evaluation and air monitoring.
Laboratory chemicals that are frequently evaluated are formaldehyde,
acrylamide, methylene chloride and other solvents, and heavy metals
such as arsenic, mercury, and beryllium.
Facilities and Shop Air Monitoring
Facilities activities and shops are covered under separate OSHA
standards but are subject to the same OSHA Permissible Exposure
Limits for chemical safety. It is the responsibility of facilities
and shop supervisors to train their employees to understand the
chemical hazards and the signs and symptoms of exposure. Exhaust
ventilation is used in shops to control paint exposure (paint spray
booths), wood dust (carpentry shops), machining fluids (lathe and
grinder hoods), and welding fume (welding slot hoods or moveable
canopies). Air sampling can be used to evaluate these exposures.
In addition, other types of monitoring can be performed. For example,
the presence of lead in painted metal surfaces can be evaluated
by a portable instrument that gives an immediate readout of the
amount of lead present. This evaluation can be done before lead
paint is removed so that appropriate steps can be taken to control
exposure.
Exposure Monitoring and Assessment
The Industrial Hygiene Program has the responsibility to provide
technical support, maintains equipment for air sampling, and has
an analytical laboratory accredited by the American Industrial Hygiene
Association for analysis of air samples. Depending upon the chemical,
air sampling can be performed by direct reading instruments, which
give an immediate readout of the air concentration, or by time weighted
average methods in which the chemical is collected on a sorbent
and then analyzed afterwards in its analytical chemistry laboratory.
The result is a measurement of chemical exposure in ppm or mg per
cubic meter, which is compared to the appropriate OSHA standard.
Under some circumstances, surface contamination of heavy metals
such as beryllium or arsenic may be evaluated. For a few selected
chemicals (arsenic and lead), biomonitoring (urine or blood screening)
is also performed by the IHP Laboratory in conjunction with the
MIT Medical Department.
Exposure monitoring is one component of exposure assessment. Exposure
assessment also includes the evaluation of other routes of exposure
(such as skin contact) and the development of protective controls
such as the use of appropriate gloves and clothing as well as exhaust
ventilation to contain exposures and reduce air levels. IHP can
visit a laboratory or shop to observe procedures and recommend changes
to controls and work practices to reduce exposures to safe levels.
IHP can be reached at 2-3477 for exposure evaluation and monitoring. |
