Certified Fire Investigator Practice Exam

What does Auto-ignition refer to?

1. Ignition with the presence of an external spark

2. Combustion initiated by heat without a spark or flame

3. The ignition of a fire due to a chemical reaction

4. Flame propagation due to wind

The correct answer is: Combustion initiated by heat without a spark or flame

Auto-ignition refers to the process where combustion is initiated solely by the heat of a substance without the need for any external spark or flame. This phenomenon occurs when a material's temperature rises to a point where it can ignite spontaneously due to the internal energy generated from factors such as high temperature, pressure, or chemical reactions. For instance, certain materials can reach their auto-ignition temperature when heated, leading to combustion even in the absence of a flame or spark. This is critical in various safety contexts because it implies that hazardous conditions can arise from heat alone, emphasizing the importance of temperature control and monitoring in environments where flammable materials are present. The other options do not accurately describe auto-ignition. While ignition with an external spark involves an external energy source, auto-ignition specifically does not require this. The ignition of a fire due to a chemical reaction may involve reactions that produce heat, but not all chemical reactions will result in auto-ignition. Flame propagation due to wind refers to the spread of an existing fire rather than the initiation of combustion. Thus, the clear alignment of auto-ignition with heat-induced spontaneous combustion underlines why the second choice is the correct answer.