What does IDLH stand for?

What does IDLH mean?

IDLH	Immediately Dangerous to Life or Health Academic & Science » Electronics
IDLH	Immediate Danger to Life or Health Governmental » US Government
IDLH	Industrial Dust Lung Hazard Governmental » Environmental
IDLH	Immediately Dangerous to Life and Health Governmental » Environmental
IDLH	Immediately Dangerous to Life and Health Governmental » NASA
IDLH	immediately dangerous to life or health concentration Medical » Physiology