What does the flammable range refer to in fire investigation?

The flammable range, also known as the explosive range, specifically refers to the concentration of a gas or vapor in the air that is required for ignition to occur. This range is defined by its lower and upper limits: the lower explosive limit (LEL) and the upper explosive limit (UEL). Within this range, the mixture of gas and air is present in a proportion that can sustain combustion if an ignition source is introduced.

Understanding the flammable range is crucial in fire investigation, as it helps determine whether a particular environment poses a risk for a fire or explosion. Insufficient or excessive amounts of gas in the air will not lead to ignition, thus underscoring the importance of knowing the flammable range for safety and investigative purposes.

In contrast, the other choices refer to different aspects of fire dynamics and do not define the flammable range itself. The speed of flame spread relates to how quickly fire propagates through materials rather than the concentration needed for ignition. The temperature for ignition, often referred to as the ignition temperature or flash point, indicates the heat needed to ignite a material but does not involve the gas-air mixture proportions. The amount of fuel available pertains to the fuel load in a fire scenario rather than the specific concentration criterion for