Office of Research

II. Employee Exposure

Criteria used to determine and implement control measures to reduce employee exposure to hazardous chemicals include engineering controls, the use of personal protective equipment, and proper chemical and personnel hygiene practices and procedures. Particular attention shall be given to the selection of control measures for chemicals that are known to be extremely hazardous.

The American Conference of Governmental Industrial Hygienists (ACGIH) produces annual lists of Threshold Limit Values (TLV’s) and Short Term Exposure Limits (STELS) for common chemicals used in laboratories. These values are guides, not legal standards (but can be enforced by OSHA under the General Duty Clause as consensus standards, especially if there is no corresponding PEL. They are defined as follows:

TLV-Time-weighted average concentration for a normal 8-hour workday to which nearly all workers may be repeatedly exposed without adverse effect.

STEL-Maximum concentration to which workers can be exposed for periods up to 15 min. Such exposures should be limited to no more than four per day with periods of at least 60 min each between exposures; the total time-weighted exposure per day should not exceed the TLV value.

The TLVs provide a useful estimate of how much ventilation may be needed in laboratories where the occupants typically spend most of their working time. However, because of the many factors influencing toxicity, each situation should be evaluated individually and the TLVs used as guidelines rather than as fine lines between safe and dangerous concentrations.

The best way to avoid exposure to toxic vapors, mists, gases, and dusts is to prevent the escape of such materials into the working atmosphere and to ensure adequate ventilation by the use of exhaust hoods and other local ventilation.


Avoid Exposure:

  1. Know the safety rules and procedures that apply to the work that is being done. Determine the potential hazards (e.g., physical, chemical, biological) and appropriate safety precautions before beginning any new operation.
  2. Know the location of and how to use the emergency equipment in your area, as well as how to obtain additional help in an emergency, and be familiar with emergency procedures.
  3. Know the types of protective equipment available and use the proper type for each job.
  4. Be alert to unsafe conditions and actions and call attention to them so that corrections can be made as soon as possible. Someone else’s accident can be as dangerous to you as any you might have.
  5. Do not consume or store food or beverages or smoke in areas where chemicals are being used or stored.

A.   General Requirements

1.    Employee Exposure Determination

a.     Initial Monitoring

The Department of Environmental Health and Safety will measure an employee’s exposure to any substance regulated by a standard which requires monitoring if there is reason to believe that exposure levels for that substance routinely exceed the action level (or in the absence of an action level, the permissible exposure level).

b.     Periodic Monitoring

If the initial monitoring discloses employee exposure over the action level (or in the absence of any action level, the PEL), the exposure monitoring provisions of the relevant standard will be followed.

c.     Termination of Monitoring

Monitoring may be terminated in accordance with the relevant standard.

d.     Employee Notification of Monitoring

A copy of the results of such monitoring will be sent to the employee or employees involved (or posted in an appropriate location near the area tested) within 15 days of receipt of the test results. The Office of Environmental Health and Safety will maintain an official record of the results.


2.     Chemical Spills or Leaks

In the case of a spill, if the spill is a small amount (less than one liter) inside a fume, the spill should be cleaned up immediately using the proper personal protective equipment (PPE required for cleanup) and appropriate absorbent material (Consult the material safety sheet for information on spill cleanup). If the spill occurs outside the hood, amounts of one liter or less of low toxicity materials may be cleaned up by trained laboratory personnel only if the proper cleanup materials and personal protective equipment required for cleanup are used. If Chemicals of high toxicity are spilled outside chemical hoods, alert other personnel in the area, evacuate the area, close the laboratory door and call 911. (Refer to Appendix C for further information on spill cleanup and response)


3.     Odor Detection

Detection of odors is not a reliable means of judging the hazard of an exposure. There are several variables in the odor threshold, and variables in human detection of odor.

There are some materials which have a strong or easily-detected odor at concentrations which are far below any level at which health hazards are likely to occur. For example, mercaptans and ethyl ether have such low odor thresholds that they give an early warning of their presence.

Other toxic materials are odorless or cannot be detected at concentrations below the permissible exposure limits. The ability to perceive odor varies among individuals and not everyone can smell odors of certain chemicals which may be extremely toxic, such as hydrogen cyanide or hydrogen sulfide. Other individuals exposed to odorous chemicals day to day may eventually experience a diminished or complete inability to detect certain odors.

The ability to perceive odor may also vary depending on interfering odors and with time and concentration. After a short exposure to some strong chemical odors (e.g., phosgene, formaldehyde, and hydrogen sulfide), olfactory fatigue may occur so that a person is no longer able to smell the odor. If olfactory fatigue does occur, a person may be in great danger because he thinks the exposure no longer exists.

As an example, hydrogen sulfide has the strong odor of rotten eggs and can be detected at concentrations as low as 0.025 parts per million (ppm). It is distinct at 0.3ppm, offensive and moderately intense at 3-5ppm and strong but not intolerable at 20-30ppm. (The maximum concentration allowable for a prolonged or work-day exposure is 20ppm).


4.     Signs and Symptoms of Overexposure

While your senses may not give you precise information, there is a lot you and your co-workers can find out by perceptive observation not only of the working conditions, but of your own sensations.

There are two classes of adverse health effects you may be able to perceive:

1.     Signs - evidence which is observable by others

2.     Symptoms - evidence which is subjective and not observable by others

Signs of Inhalation Exposure

If you suddenly begin sneezing or coughing, your eyes begin to water, or your gait becomes staggered, these are signs observable by yourself (as well as by others) that you could possibly be exposed to irritating gases or vapors. Changes in breathing rate could be another sign of exposure.

Symptoms of Inhalation Exposure

Symptoms of exposure to irritating gases or vapors include: headache, irritation of eyes, nose, and throat; increased secretion of mucous in your nose and throat; and other subjective evidence.

Signs of Skin Contact

In case of skin exposure to chemicals, you may see signs of redness (erythema), swelling (edema), or dry whitened skin. You may experience symptoms of irritation and itching.

The skin on your hands may become dry and whitened if you wash residues off your hands with organic solvents. This results from removing some of the lipids from the surface of your skin. Repeated or prolonged contact with solvents is likely to lead to cracked and red skin or dermatitis, which can be a lifelong problem.

Other Signs and Symptoms of Chemical Overexposure

Potentially hazardous exposures may be recognizable from fairly obvious signs or symptoms, but such evidence may be overlooked or ignored if you are not prepared to observe it. In addition to some easily recognizable signs, there can be subtle effects that need to be recognized. Here is a list of some of the subtle signs and symptoms which can be caused by chemical exposures (or which could also be caused by other factors, including illness):

    • Changes in normal behavior patterns
    • Periods of dizziness
    • Muscle spasms
    • Irritability

Some of these signs and symptoms may occur in a short time, while others may not be noticed unless the exposure is several days in length.

Be prepared to get out of the area if symptoms appear suddenly. If the symptoms disappear or alleviate quickly once you are out of the area, alert you supervisor and others in the area.

If care is taken to ensure that  (1) the ventilation system (including the hood) is performing and being used properly (2) the laboratory workers are using proper protective clothing to avoid skin contact and (3) the laboratory workers are following good hygiene and laboratory safety practices, then even highly toxic materials can be handled without undue risk.

B.        Laboratory Specific Criteria 

Place Hazard Assessments based on laboratory specific criteria for the selection of personal protective equipment for specific chemical procedures, here