An "IDLH" value, or Immediately Dangerous to Life or Health, represents the atmospheric concentration of a toxic, corrosive, or asphyxiant substance that poses an immediate threat to life

 https://dramarnathgiri.blogspot.com/2025/01/immediately-dangerous-to-life-or-health.html

An "IDLH" value, or Immediately Dangerous to Life or Health, represents the atmospheric concentration of a toxic, corrosive, or asphyxiant substance that poses an immediate threat to life, could cause irreversible or delayed adverse health effects, or interfere with an individual's ability to escape a dangerous atmosphere. 

Here's a more detailed explanation:

Purpose:

IDLH values are established to ensure that workers can escape a contaminated environment even if their respiratory protection equipment fails, and to indicate the maximum level above which only highly reliable breathing apparatus should be used. 

Development:

NIOSH (National Institute for Occupational Safety and Health) develops IDLH values based on scientific rationale and logic, including in-depth literature searches of human and animal studies with acute exposures to the substance. 

Considerations:

The development of IDLH values involves evaluating studies, including species, study protocols, exposure concentrations and durations, health endpoints, and critical effect levels. 

Use in Workplace:

IDLH values are crucial for selecting appropriate respirators and other safety measures in workplaces where hazardous substances are present. 

Example:

The IDLH value for chlorine is 10 ppm, meaning that exposure to 10 ppm or more of chlorine could be immediately dangerous to life or health. 

Not Oxygen Deficiency:

The NIOSH definition of IDLH does not include oxygen deficiency (below 19.5%). 

Historical Context:

The original IDLH values were developed in the 1970s and revised in 1994. 

NIOSH Website:

More information on IDLH values can be found on the NIOSH website. 

Other Agencies:

The Occupational Safety and Health Administration (OSHA) also uses IDLH values in its regulations and guidance. 

Public Exposure:

While primarily a workplace exposure limit, IDLH values have historically been used in public exposure situations before separate public exposure guidelines were commonly available.