IDLH Situations

If the concentration or type of hazard in the area is considered to be immediately dangerous to life or health (IDLH), only certain respirators can be used. Examples of IDLH atmospheres include the following:

• More than 100 milligrams per cubic meter of lead dust or fumes
• More than 2,440 milligrams per cubic meter of chloroform
• More than 210 milligrams per cubic meter of ammonia
• Air containing less than 17 percent oxygen

NIOSH provides a table that lists hundreds of compounds and the concentrations that can create an IDLH atmosphere*. Employers can consult this table before working with a particular substance to know whether the concentrations found at the workplace are considered IDLH. As the sixteenth-century German-Swiss physician Paracelsus famously put it, "Poison is in everything, and no thing is without poison. The dosage makes it either a poison or a remedy."

If an atmosphere is considered IDLH, employers must provide one of the following respirators:

• A full facepiece SCBA in pressure-demand mode, certified by NIOSH for a minimum service life of 30 minutes
• A combination full facepiece SAR in pressure demand mode, with an auxiliary self-contained air supply

If a respirator is to be used only for escape or rescue from an IDLH atmosphere (for instance, in a catastrophic emergency rather than during daily activities), it must be certified for escape by NIOSH.

To learn more about Respiratory Protection visit our Cal/OSHA Respiratory Protection Online Training web page.