How is explosivity expressed in relation to a material?

Explosivity is expressed as a percentage of a given material in a volume of air because this measurement indicates the concentration of combustible gases or vapors needed for combustion to occur when mixed with air. In the context of gas and vapor safety, the explosive limits are often defined in terms of lower and upper explosive limits (LEL and UEL), which describe the minimum and maximum concentrations of the flammable material in air that can lead to an explosion. This percentage-based approach allows for a clear understanding of the conditions under which an explosive atmosphere can form, which is crucial for safety assessments in environments where flammable materials are present. Understanding the explosive concentration in relation to the volume of air is essential for professionals managing risks associated with underground storage tanks and other potential sources of hazardous materials.