Ceiling Limit (C)

A ceiling limit is the concentration that must never be exceeded during any part of the working exposure. Unlike TWA or STEL, there is no averaging period for a ceiling limit- it is an absolute maximum. If a substance has a ceiling value, workers must not be exposed to concentrations above this level, even momentarily. Some substances also have “peak” limits, allowing very brief excursions above the ceiling under specific conditions.

In addition to ceiling limits, some chemicals will have levels designated as Immediately Dangerous to Life and Health (IDLH). This is not an enforceable level, but should not be exceeded. These levels are often set by research organizations and are used to set the ceiling limit.