IDLH, an environment Immediately Dangerous to Life and Health, defined by OSHA as follows: "an atmospheric concentration of any toxic, corrosive or asphyxiant substance that poses an immediate threat to life, would cause irreversible adverse health effects, or would interfere with an individual's ability to escape from a dangerous atmosphere." Examples include smoke or poisonous gases. Does not technically include areas with oxygen deficiency (below 19.5 percent) where breathing apparatus is also required.
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