What are flammable and explosive limits?

Flammable and explosive limits refer specifically to the upper and lower concentrations of a vapor in the air that can ignite and produce a flame. This concept is critical in fire prevention and safety because it helps determine the conditions under which a combustible vapor can ignite, creating a fire hazard.

When the concentration of a vapor falls below the lower explosive limit (LEL), there is insufficient fuel for combustion, while if the concentration exceeds the upper explosive limit (UEL), there is too much fuel and not enough oxygen for ignition. Thus, understanding these limits is essential for ensuring safety when working with volatile substances, as it dictates the conditions to avoid potential ignition during handling or storage.

The other options, while relevant to fire safety, do not accurately define flammable and explosive limits. Pressure measurements do not pertain to concentration levels of vapors. Similarly, temperature ranges for ignition refer more to flash points rather than to the specific concentration limits within which combustion can occur. The physical state of materials at the flash point addresses the conditions required for ignition but does not encompass the concept of explosive limits directly.