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Safety Terms for Science Teachers

Chemical Exposure


Routes of Exposure

Chemicals in the form of gases, vapors, mists, fumes, and dusts can enter through the nose or mouth and be absorbed through the mucous membranes of the nose, trachea, bronchi, and lungs.

Chemicals can enter the body through the mouth and be swallowed . They may be  absorbed into the bloodstream anywhere along the length of the gastrointestinal tract.

Although the skin is a good barrier to many substances, some chemicals can be absorbed through the skin, enter the bloodstream, and be carried throughout the body.

While uncommon in most workplaces, exposure to a chemical can occur when a sharp object (e.g., a needle or broken glass) punctures the skin and injects a chemical directly into the bloodstream.

Types of Exposure Limits

Permissible exposure limit (PEL)
Specifies the maximum amount or concentration of a chemical to which a worker may be exposed. It can be established in one of two ways:  

  1. Ceiling values: At no time should this exposure limit be exceeded.
  2. 8-hour time-weighted average (TWA): An average value of exposure over the course of an 8-hour work shift.

Threshold limit value (TLV)
Denotes the level of exposure that nearly all workers can experience without an unreasonable risk of disease or injury. Defined as ceiling limits, short-term exposure limits (STEL), and TWAs . It should be noted that these are only advisory limits and not enforceable by law. These may be the same as PELs.

TLVs are produced by the American Conference of Governmental Industrial Hygienists (ACGIH).

Immediate danger to life or health (IDLH)
Specifies a level of exposure that is immediately dangerous to life and/or health.

Following are terms asccociated with chemical exposure that all science teachers should know. It is helpful to include these terms when discussing RAMP and safe chemical handling in the laboratory.

Allergen (sensitizer)

A chemical that causes an allergic reaction— that is, evokes an adverse immune response (could be a severe rash or respiratory distress).


A gas or vapor that can cause unconsciousness or death by suffocation due to lack of oxygen.

Autoignition temperature

The temperature at or above which a substance will spontaneously ignite or catch fire without a spark or flame.


A substance that is capable of causing cancer.


A highly reactive substance that causes obvious damage to living tissue by chemical action. Examples of corrosive substances are strong acids, strong bases, and oxidizing agents.


Direct contact with a hazard or chemical in a way that causes injury or harm.

Exposure Limit

The established concentration of a chemical that most people could be exposed to in a typical day without experiencing adverse effects. Following are the various types of exposure limits. Exposure limits help in understanding the relative risks of chemicals.


A substance that enters the maternal and placental circulation and causes injury or death to the fetus.


A substance that easily catches fire. As defined by the GHS, a flammable substance is one that has a flash point at or above 73 °F (23 °C) and below 140 °F (60 °C). A highly flammable substance has a flash point below 73 °F (23 °C) and an initial boiling point above 95° F (35° C). An extremely flammable substance has a flash point below 73° F (23° C) and an initial boiling point below 95° F (35° C).1

Flash point

The lowest temperature at which a liquid or solid can produce a vapor sufficient to form an ignitable mixture in the air. The lower the flash point, the easier it is to ignite the material.


A substance capable of changing genetic material in a cell and thus increasing the frequency of mutations.

Runaway reaction

An unexpected event in which the rate of reaction increases significantly, resulting in a significant increase in temperature. The increase in temperature causes the rate of reaction to increase, further increasing the rate and tending to create an uncontrolled, often heat-producing, reaction.


An agent that can cause non-inheritable genetic mutations or malformations of an embryo or fetus. The agent can be a chemical substance, virus, or ionizing radiation.


Any substance that has the capacity to produce personal injury or illness to humans through ingestion, inhalation, or absorption through any body surface, as defined by Federal Hazardous Substances Act (FHSA) regulation.

Acute toxicity

The adverse effects of a substance resulting from a single exposure or multiple exposures over a very short time span (less than 24 hours). Acute toxicity is usually determined by exposing animals to a given chemical to determine the lethal dose, 50% (LD50). This is an experimental measure determined by administering varied doses of a chemical by some route to animals, observing the percentage lethality at these doses, and extrapolating to estimate the dose that would kill 50% of the animals.

Chronic toxicity

Adverse effects resulting from long-term exposure, usually at lower levels, to a substance.

Types of Acute Toxicants

A gas or vapor that can cause unconsciousness or death by suffocation due to lack of oxygen.    

  • Examples: Carbon monoxide, methane, hydrogen sulfide

A noncorrosive chemical that causes reversible inflammation at the point of contact with the skin.

  • Examples: Acetone, heptane, ethyl acetate, sodium carbonate

A chemical that interferes with the peripheral and central nervous systems.

  • Examples: Mercury, lead, acetone, carbon disulfide

Organ toxicant
A chemical that adversely affects one or more organs or body systems.

  • Examples: Toluene, carbon tetrachloride, arsenic, chlorine

A chemical that produces its effects by evoking an adverse response in the body’s immune system.

  • Examples: Formaldehyde, latex

Teratogen or fetotoxicant
A chemical that adversely affects the embryo or fetus.

  • Examples: Ethanol, ethylene oxide, mercury compounds

Chronic toxicity

Adverse effects resulting from long-term exposure, usually at lower levels, to a substance.

Examples of Chronic Toxicants2


  • Examples: Ethylene oxide, Cr(VI) formaldehyde, arsenic


  • Examples: Carbon disulfide, hexane, lead, nicotine, arsenic

Organ toxicant

  • Examples: Mercury, ethanol, beryllium, chloroform

1 Source: UNECE. Globally Harmonized System of Classification and Labelling of Chemicals, 2015. (accessed Dec 1, 2015).


2 Source: Hill, R. H.; Finster, D. C. Laboratory Safety for Chemistry Students; John Wiley & Sons, Inc.: Hoboken, NJ, 2010; pp 4-1 to 4-34.

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