What do we call the range of percentages of a substance in the air that can burn when ignited?

The term referring to the range of percentages of a substance in the air that can burn when ignited is known as flammable limits or flammable range. This concept encompasses both the lower flammable limit (LFL) and upper flammable limit (UFL), which define the concentration of a vapor in air necessary for ignition to occur. If the concentration is below the LFL, the mixture is too lean to burn, and if it's above the UFL, it's too rich to sustain combustion. Understanding these limits is crucial for fire prevention and safety in various environments, especially in industries where flammable materials are handled.

While the other terms like ignition limits and fire limits may relate to combustion phenomena, they do not specifically encompass the dual concept of lower and upper limits that defines when combustion can occur in the presence of air. Combustion range is also a less commonly used term and does not convey the specific scientific context of concentration ranges as accurately as flammable limits/range. Thus, the correct answer highlights this essential concept in fire safety and risk assessment.