In OSHA’s Guidance for Hazard Determination for Compliance, acute toxicity is defined as “the toxic effects resulting from a single dose or short exposure to a substance.” Adverse effects caused by acute toxicity can happen if a chemical is ingested, absorbed through the skin, or inhaled, specifically in small doses or for short amount of time (typically less than 24 hours).
The Globally Harmonized System established classification for acute toxicity with five different categories; category 1 represents the most severe toxicity. OSHA has adopted the tiered approach developed by GHS but reclassified category 5 to be listed as a hazard not otherwise classified (HNOC).
These categories are determined by experimental data. Common methods for collecting this kind of data include investigations into accidental human exposures, testing on animals, and in vitro testing methods. One way they measure short-term toxicity is to find the LD50 using lab rats. LD50 is the amount (Lethal Dose) of the chemical which causes the death of 50% of the test animals. The LD50 will need to be determined for each method of entry (oral, dermal, or inhalation).
This data is also used by OSHA and the American Conference of Governmental Industrial Hygienists (ACGIH) to define short-term exposure limits:
- STEL is the official acronym to represent the “concentration which no person should be exposed to for more than 15 minutes during an 8-hour work day.”
- Ceiling Value (CV) is the threshold limit meaning it is the concentration at which no individual should be exposed to.
These limits should be detailed in the safety data sheet (SDS)
On a GHS label, hazard pictograms are used to represent acute toxicity; fatal or toxic acute toxicity requires a skull & crossbones pictogram while pictograms with an exclamation point are used for acutely toxic (harmful) chemicals. If workers are exposed to an acutely toxic dose of a substance, it must be treated immediately. Having accessible emergency showers and emergency eye wash stations are critical for minimizing harmful effects.