What is the flammable vapor mixture range considered explosive?

What is the flammable vapor mixture range considered explosive?

• A. Less than 1%
• B. 1% to 8%
• C. More than 8%
• D. No valid range

Answer: (B)

The concept is that flammable vapors form an explosive mix only within a specific concentration range in air. This range is defined by the lower and upper flammable limits (LEL and UEL). When the vapor concentration is between these limits, an ignition source can start and sustain combustion; outside this range, ignition is unlikely—too lean below the LEL or too rich above the UEL. For many common fuels, that explosive range is about 1% to 8% by volume in air. So, a vapor concentration of 1% to 8% is considered explosive, while lower than 1% or higher than 8% is not.

The concept is that flammable vapors form an explosive mix only within a specific concentration range in air. This range is defined by the lower and upper flammable limits (LEL and UEL). When the vapor concentration is between these limits, an ignition source can start and sustain combustion; outside this range, ignition is unlikely—too lean below the LEL or too rich above the UEL.

For many common fuels, that explosive range is about 1% to 8% by volume in air. So, a vapor concentration of 1% to 8% is considered explosive, while lower than 1% or higher than 8% is not.