Hazardous atmosphere may expose employees to the risk of death, incapacitation, or loss of their ability to escape unaided from a permit space injury, or acute illness from the following causes:

  1. Flammable gas, vapor, or mist in excess of 10 percent of its lower flammable limit (LFL);
  2. Airborne combustible dust at a concentration that meets or exceeds its LFL;
  3. Atmospheric oxygen concentration below 19.5 percent or above 23.5 percent;
  4. Atmospheric concentration of any substance for which a dose or a permissible exposure limit is published in Article 4 of the Construction Safety Orders and Group 16 of the General Industry Safety Orders;
  5. Any other atmospheric condition that is immediately dangerous to life or health.