Isolated flames in the gas layer during the growth stage indicate which condition?

Isolated flames in the gas layer during the growth stage indicate which condition?

• A. Hot and cool gases are mixing.
• B. The oxygen concentration level is high.
• C. The temperature is too low for full ignition.
• D. Portions of the gas layer are within flammable range.

Answer: (D)

Pockets of isolated flame in the gas layer show that some portions of the air-fuel mixture have reached the flammable range. When heat from the growing fire vaporizes more fuel and creates a stratified layer near the ceiling, small pockets can mix with enough oxygen to fall between the lower flammable limit (LFL) and upper flammable limit (UFL). In those pockets, an ignition source can light the vapor-air mix without the entire layer lighting up, which is why you see isolated flames rather than a uniform flame throughout the layer. The key idea is the presence of fuel vapor concentration within flammable limits in those specific spots.

Pockets of isolated flame in the gas layer show that some portions of the air-fuel mixture have reached the flammable range. When heat from the growing fire vaporizes more fuel and creates a stratified layer near the ceiling, small pockets can mix with enough oxygen to fall between the lower flammable limit (LFL) and upper flammable limit (UFL). In those pockets, an ignition source can light the vapor-air mix without the entire layer lighting up, which is why you see isolated flames rather than a uniform flame throughout the layer. The key idea is the presence of fuel vapor concentration within flammable limits in those specific spots.