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Animals are exposed to the test substance in a stepwise procedure using the appropriate fixed concentrations for vapours, dusts/mists or gases. Initial concentration levels are selected on the basis of a sighting study at the concentration expected to produce clear signs of toxicity without causing severe toxic effects or mortality. Further animals may be tested at higher or lower fixed concentrations, depending on the presence or absence of signs of toxicity or mortality. This procedure continues until i) the concentration causing evident toxicity or no more than one death is Identified; ii), or when no effects are seen at the highest concentration; or iii) or when deaths occur at the lowest concentration.
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