“Immediately Dangerous to Life or Health” (IDLH) is a term used to describe hazards in which an acute exposure to the hazard poses a severe risk of immediate health damage, injury, or death. This immediate danger could be a result of the high level of damage that could occur due to short-term exposure to the hazard or due to the hazard’s ability to impair the ability of the employee to leave the hazard area.
The IDLH designation was developed by the National Institute for Occupational Safety and Health (NIOSH), a division of the CDC, in the mid-1970s. NIOSH's IDLH values provide guidance for employers regarding their obligations to provide respiratory protection equipment to employees facing exposure to relevant hazards. Specifically, IDLH values were established to ensure that workers have sufficient-enough safety protection to escape from an IDLH-contaminated environment if their respiratory equipment fails, as well as to provide a level of contamination above which only workers wearing a highly reliable breathing apparatus with maximum respiratory protection are permitted in the area.
The primary purpose of the IDLH term is to provide guidance in the selection of respiratory use. Environments that are contaminated with hazardous substances at a level that has been recognized as immediately dangerous to life or health are referred to as “IDLH environments.” NIOSH regularly updates these values.
Until 1994, IDLH was associated with exposure durations of 30 minutes. However, there is now no exposure duration associated with an IDLH, which means that workers should not be in an IDLH environment for any length of time without being equipped with adequate protective equipment. NIOSH lists more than 380 substances with IDLH values. These values are selected to demarcate the level after which exposure to a particular atmospheric concentration of a toxic, corrosive, or asphyxiant substance would pose an immediate threat to life, cause irreversible or delayed negative health effects, or interfere with an individual's ability to escape from the environment.
OSHA has referred to its Hazardous Waste Operations and Emergency Response standard (HAZWOPER, 1910.120) for interpreting what its standards require for workers operating within IDLH environments. This standard requires that a buddy system be used within the hazardous area, with one “buddy” employee focusing on observing his or her partner working and thus monitoring for negative health effects and providing rescue if needed. Additionally, the standard requires that two additional personnel should be available immediately outside the hazardous area to provide rescue and assistance to both workers if needed.