If a fuel is below the lower explosive limit or above the upper explosive limit, what is the combustion state?

When a fuel is below the lower explosive limit (LEL) or above the upper explosive limit (UEL), it indicates a condition where combustion is not possible. In the case of being below the LEL, there is an insufficient concentration of fuel in the air necessary to support combustion. This means that the mixture lacks sufficient combustibles to ignite and sustain a fire. Therefore, the correct answer points to the lack of adequate fuel concentration for combustion.

On the other hand, if the fuel concentration exceeds the UEL, there is too much fuel for combustion to occur, and not enough oxygen available in the mixture, which also prevents combustion. In both scenarios, the fuel cannot reach the necessary conditions for ignition and sustained combustion.

This understanding is fundamental in fire investigation, as it helps in determining the conditions necessary for a fire to ignite and spread. Recognizing the significance of the limits allows investigators to assess fire scenes more accurately and understand the mechanisms of fire behavior in relation to fuel availability.