It is the principle of the test that based on a stepwise procedure, sufficient information is obtained on the acute inhalation toxicity of the test article during an exposure period of 4 hours to enable its classification. Other durations of exposure may apply to serve specific regulatory purposes. At any of the defined concentration steps, 3 animals of each sex are tested. Depending on the mortality and/or the moribund status of the animals, 2 steps may be sufficient to allow judgement on the acute toxicity of the test article. If evidence is provided that one sex is more susceptible than the other, then the test may be continued with the more susceptible sex only. The outcome of the previous step will determine the following step such that:
a) No further testing is needed, b) Testing of three animals per sex, or c) Testing with 6 animals of the more susceptible sex only i.e. the lower boundary estimates of the toxic class should be based on 6 animals per test concentration group, regardless of
Further information: http://iccvam.niehs.nih.gov/SuppDocs/FedDocs/OECD/OECD-TG436.pdf