Industrial hygiene or occupational hygiene is the anticipation, recognition, evaluation, control, and confirmation of protection from hazards at work that may result in injury, illness, or affect the well‐being of workers. These hazards or stressors are typically divided into the categories biological, chemical, physical, ergonomic, and psychosocial. The risk of a health effect from a given stressor is a function of the hazard multiplied by the exposure to the individual or group. For chemicals, the hazard can be understood by the dose response profile most often based on toxicological studies or models. Industrial hygienists work closely with toxicologists for understanding chemical hazards, physical therapist for physical hazards, and physicians and microbiologists for biological hazards. Environmental and industrial hygienists are considered experts in exposure science and exposure risk management. Depending on an individual’s type of job, a hygienist will apply their exposure science expertise for the protection of workers, consumers, and/or communities (Johnson 2017).
Toxicology
The degree to which a substance is poisonous is termed its toxicity. A toxicant is any chemical substance which when inhaled, ingested, absorbed through the skin or when applied to, injected into, or developed within the body, in relatively small amounts may cause, by its chemical reaction, damage to the body structure or disturbance to human function or even death. Most chemicals enter the body through respiratory tract, digestive tract, eyes, and skin. Two levels of toxicity are defined: (i) acute “short‐term” exposure that causes initiation poisoning, (ii) chronic “long‐period” exposure that causes anemia, leukemia, and death.
TLVs and Exposure Limits
Toxic TLVs are the greatest concentrations of a toxicant in air that can be tolerated for a given length of time without any toxic effects. Definitions of commonly used limit values are given in the following.
The different types of TLVs and exposure limits are as follows:
| TLV‐TWA | The TWA for a normal 8‐hour workday or 40‐hour work week to which a worker may be exposed without adverse effect |
| TLV‐STEL | The short‐term exposure limit is the maximum concentration to which a worker may be exposed continuously up to 15 minutes without adverse effect |
| TLV‐C | The ceiling limit is the concentration which should not be exceeded at any time |
| PEL | Permissible exposure limit is the maximum exposure allowed by OSHA 29CFR1910.1000 |
| IDLH | Immediately dangerous to life or health. It is the maximum concentration from which one could escape within 30 minutes without escape‐impairing symptoms or any irreversible health effects |
TLVs are expressed either in parts per million by volume (ppm) or milligram per cubic meter (mg/m3).
where
- P = pressure in atm;
- T = temperature in K;
- M = molecular mass
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