When the air mixture is too lean for a substance to burn, this condition is referred to as?

When the air mixture is too lean for a substance to sustain combustion, this condition is referred to as being below the lower explosive limit (LEL). The lower explosive limit represents the minimum concentration of a flammable substance in air that is required for a fire to occur. If the concentration of the flammable substance is lower than this limit, there is not enough material present to ignite and burn, regardless of the ignition source present.

The concept of LEL is critical in understanding fire safety and hazardous materials management, as it helps in assessing the conditions under which a fire could potentially start. When operating below this limit, the mixture is considered too lean to support combustion, which is a critical aspect for personnel involved in hazardous materials situations.