An IDLH (Immediately Dangerous to Life or Health) environment is a setting where conditions pose an immediate threat to life or health or could cause severe, irreversible harm without proper protection measures. These extreme conditions - commonly found in fully involved structure fires - expose firefighters to high temperatures, toxic gases, and heavy smoke, putting their safety at significant risk.

The fire tetrahedron is a key part of suppression solutions and fire safety. This model builds on the traditional fire triangle by introducing a critical fourth element: the chemical chain reaction. Fire suppression systems are developed to combat these elements, focusing on disrupting the chain reaction that keeps fires burning.