What is defined as the minimum temperature required to ignite gas or vapor without a spark or flame?

The minimum temperature required to ignite gas or vapor without the presence of a spark or flame is known as the autoignition temperature. This value is crucial in safety and risk assessments within environments where flammable gases or vapors are present. At or above this temperature, the material can spontaneously ignite due to thermal energy alone.

Understanding the autoignition temperature is essential for creating safety protocols, as it guides operational limits preventing unintentional fires. For example, if a material has a low autoignition temperature, safety measures must be in place to ensure the temperature in its vicinity does not reach this point.

The other terms relate to different aspects of combustion and flammability. The flash point refers to the lowest temperature at which a liquid can form an ignitable mixture in air, but it does require an external ignition source. The lower explosive limit denotes the lowest concentration of vapor in air that can support combustion, which is different from a temperature measure. Finally, the fire point is the minimum temperature at which a liquid generates enough vapor to sustain combustion once ignited. Each of these concepts plays a role in understanding and managing fire hazards, but it’s the autoignition temperature that specifically pertains to spontaneous ignition without an external spark or flame.