an auxiliary pressure-demand self-contained breathing apparatus. IDLH values The following examples are listed in reference to IDLH values. Legend: Ca NIOSH considers this substance to be a potential occupational carcinogen. Revised values may follow in parentheses. N.D. Not determined. That is, the level is unknown, not non-existent. 10%LEL The IDLM value has been set at 10% of the lower explosive limit although other irreversible health effects or impairment of escape due to toxicology exist only at higher levels. See also NIOSH air filtration rating References External links NIOSH IDLH site 1910.134(b) Respiratory protection definitions Chemical safety Firefighting in the United States Occupational Safety and Health Administration National Institute for Occupational Safety and Health