TABLE 4.2 Probable Lethal Dose for Humans

Toxicity Rating

Animal LD50(per kg)

Lethal Dose When Ingested by 70-kg (150-lb) Human

Extremely toxic

<5 mg

A taste (<7 drops)

Highly toxic

5 to 50 mg

Between 7 drops and 1 tsp

Moderately toxic

50 to 500 mg

Between 1 tsp and 1 oz

Slightly toxic

500 mg to 5 g

Between 1 oz and 1 pint

Practically nontoxic

>5 g

>1 pint

SOURCE: Modified, by permission, from Gosselin et al. (1984); reprinted by permission from Lippincott Williams and Wilkins,

section 6.D. In some circumstances, all these special precautions may not be necessary, such as when the total amount of an acutely toxic substance is a small fraction of the harmful dose. An essential part of prudent experiment planning is to determine whether a chemical with a high degree of acute toxicity should be treated as a PHS in the context of a specific planned use. This determination not only involves consideration of the total amount of the substance to be used but also requires a review of the physical properties of the substance (e.g., Is it volatile? Does it tend to form dusts?), its potential routes of exposure (e.g., Is it readily absorbed through the skin?), and the circumstances of its use in the proposed experiment (e.g., Will the substance be heated? Is there likelihood that aerosols may be generated?). Depending on the laboratory personnel’s level of experience and the degree of potential hazard, this determination may require consultation with supervisors and safety professionals.

Because the greatest risk of exposure to many laboratory chemicals is by inhalation, trained laboratory personnel must understand the use of exposure limits that have been established by agencies such as OSHA and NIOSH and by an organization such as ACGIH.

The TLV assigned by the ACGIH, defines the concentration of a chemical in air to which nearly all individuals can be exposed without adverse effects. These limits reflect a view of an informed scientific community and are not legal standards. They are designed to be an aid to industrial hygienists. The TLV time-weighted average (TWA) refers to the concentration safe for exposure during an entire 8-hour workday; the TLV-STEL is a higher concentration to which workers may be exposed safely for a 15-minute period up to four times during an 8-hour shift and at least 60 minutes between these periods. TLVs are intended for use by professionals after they have read and understood the documentation of the TLV for the chemical or physical agent under study.

TABLE 4.3 Examples of Compounds with a High Level of Acute Toxicity


Methyl fluorosulfonate


Nickel carbonyl


Nitrogen dioxide


Osmium tetroxide

Diborane (gas)


Dimethyl mercury


Hydrogen cyanide

Sodium azide

Hydrogen fluoride

Sodium cyanide (and other cyanide salts)

OSHA defines the permissible exposure limit (PEL) analogously to the ACGIH values, with corresponding 8-hour TWA and ceiling limits based on either a 15-minute TWA or an instantaneous reading, whichever is possible. In some cases, OSHA also defines a maximum peak concentration that cannot be exceeded beyond a given duration. Compliance with PELs is required, and the limits are enforceable by OSHA. PEL values allow trained laboratory personnel to quickly determine the relative inhalation hazards of chemicals. In general, substances with 8-hour TWA PELs of less than 50 ppm should be handled in a laboratory chemical hood. Comparison of these values to the odor threshold for a given substance often indicates whether the odor of the chemical provides sufficient warning of possible hazard. However, individual differences in ability to detect some odors as well as anosmia for ethylene oxide or olfactory fatigue for hydrogen sulfide can limit the usefulness of odors as warning signs of overexposure. LCSSs contain information on odor threshold ranges and whether a substance is known to cause olfactory fatigue.

Recommended exposure limits (RELs) are occupational exposure limits recommended by NIOSH to protect the health and safety of individuals over a working lifetime. Compliance with RELs is not required by law. RELs may also be expressed as a ceiling limit that should never be exceeded over a given time period, but the limit is usually expressed as a TWA exposure for up to 10 hours per day during a 40-hour workweek. As with TLVs, RELs are also expressed as STELs. One should not exceed the STEL for longer than 15 minutes at anytime throughout a workday.

A variety of devices are available for measuring the concentration of chemicals in laboratory air, so that the degree of hazard associated with the use of a chemical is assessed directly. Industrial hygiene offices of many institutions assist trained laboratory personnel in measuring the air concentrations of chemicals.

4.C.3 Types of Toxins

4.C.3.1 Irritants, Corrosive Substances, Allergens, and Sensitizers

Lethal dose and other quantitative toxicological parameters generally provide little guidance in assessing the risks associated with corrosives, irritants, allergens, and sensitizers because these toxic substances exert

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement