An Immediately Dangerous to Life & Health (IDLH) atmosphere is one that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair an individual’s ability to escape. It is an atmosphere where the potential exists where one could not escape without the aid of a respiratory protective device (RPD). Selection of RPD for work in IDLH atmospheres shall consider the method of escape in the event that the primary RPD mode fails, including level during the escape. If there is uncertainty whether the concentration is above or below IDLH, or if the contaminants are unknown the atmosphere must be considered to be IDLH.

IDLH levels may be established by national or local regulations or published by professional bodies. Typically, in Australia and New Zealand most refer to the IDLH values published by the US National Institute for Occupational Safety and Health (NIOSH) https://www.cdc.gov/niosh/idlh/default.html . In Australia as part of the incoming WEL’s list, they will also list IDLH values adopted direct from NIOSH. These may also be listed in the Safety Data Sheet (SDS)

Not all contaminants have a IDLH value, but for those that do and your workers may be exposed to these levels or above it is vitally important for the risk assessment and respiratory device selection process.

An IDLH is not considered an exposure standard as it represents a concentration that may cause harm, rather than a concentration at which no adverse effects are expected in nearly all workers. IDLH values are concentrations that may cause adverse effects. They are not workplace exposure standards and should never be used in the place of a short-term exposure limit (STEL) or peak limitation. The purpose of the values is to provide safety information in the event of accidental or unintended high exposure events and not for routine occupational exposure conditions. IDLH values may be used to help guide risk management and emergency plans. All available precautions should be taken to ensure that workers exit the environment immediately if exposures are at or near concentrations equivalent to IDLH values. Exposure should not exceed 30 minutes.

There are some situations where other environmental factors are more relevant than an IDLH value. These include:

  • where the IDLH value is above the concentration that would result in oxygen deprivation (for example, inert gases), and
  • where the IDLH value is higher than a particulate concentration that generates significant hazards from reduced visibility; such conditions may occur in processes that generate dust plumes in enclosed areas or confined spaces

Therefore, all relevant information should be considered in accidental or emergency exposure situations.

In AS/NZS 1715:2009 Table 4.6 as below provides Selection consideration of use in oxygen deficiency or IDLH atmosphere or unknown concentrations of contaminants.

AS/NZS 1715:2009 Table 4.6

Selection Considerations of use in oxygen deficiency or IDLH atmosphere or unknown concentrations of contaminants
Expected Use Equipment Remarks
Escape SCBA, quick fill type Mines-continuous supply/rechargeable for

long escape route
Work, routine Full facepiece airline with EBD Limited mobility and distance to source of

respirable air
Work, including rescue use

 

 ·         Compressed air SCBA duration: > 15 minutes

·         Compressed oxygen SCBA

·         Air-line with SCBA

 ·         Limited Duration

·         Specialist training essential

·         Limited mobility and distance to source of respirable air
Special response HAZMAT incident. No O₂ deficiency Combined gas/vapour and particulate P3 full facepiece, PAPR or air-line with filter Assessed as suitable by emergency service personnel
Work, including rescue use

Special response HAZMAT incident. O₂ deficiency

 Compressed air SCBA duration: > 15 minutes

 
Work in Confined Space Refer to relevant Regulator Confined Space code of practice ·         If oxygen deficiency is suspected then supplied air equipment is suitable

·         Limited duration only

·         Specialist training essential

 

Reference/s for further information and detail:

  • AS/NZS 1715:2009 – Selection, use and maintenance – Section 1.5.39, Table 4.6
  • SA/SNZ TS ISO 16975.1:2023 – Selection, use and maintenance – Section 7.3.1.1.2
  • Safe Work Australia WES Review – Immediately Dangerous to Life & Health notation