What are the two factors that determine how wood reacts to fire?

What are the two factors that determine how wood reacts to fire?

• A. Size of the wood and its moisture content
• B. Type of wood and its age
• C. Color and grain pattern
• D. Thickness of the finishing coating

Answer: (A)

The two factors that determine how wood behaves when exposed to fire are how thick the piece is and how much moisture it contains. Moisture content matters because water inside the wood must be heated to its boiling point and vaporized as the wood heats up. That energy use cools the surface and slows ignition, so wood with higher moisture can resist catching fire temporarily. As the heat drives off the moisture, the wood becomes drier and more susceptible to pyrolysis and burning. Dry wood, with little to no moisture left, ignites and burns more readily and vigorously. Size, or thickness, affects how quickly heat reaches the interior. Thin pieces heat through rapidly, char quickly, and can ignite or burn away fast. Larger pieces have more internal mass to heat, and a char layer forms on the outside that insulates the inner wood, delaying ignition and prolonging the time before structural failure occurs. The interior may stay intact longer, even though the surface is burning, until the heat penetrates and the wood can no longer support itself. These two factors together determine heat transfer into the wood, how long it takes to ignite, and how quickly it will burn or fail, making size and moisture content the primary determinants of wood’s fire behavior.

The two factors that determine how wood behaves when exposed to fire are how thick the piece is and how much moisture it contains.

Moisture content matters because water inside the wood must be heated to its boiling point and vaporized as the wood heats up. That energy use cools the surface and slows ignition, so wood with higher moisture can resist catching fire temporarily. As the heat drives off the moisture, the wood becomes drier and more susceptible to pyrolysis and burning. Dry wood, with little to no moisture left, ignites and burns more readily and vigorously.

Size, or thickness, affects how quickly heat reaches the interior. Thin pieces heat through rapidly, char quickly, and can ignite or burn away fast. Larger pieces have more internal mass to heat, and a char layer forms on the outside that insulates the inner wood, delaying ignition and prolonging the time before structural failure occurs. The interior may stay intact longer, even though the surface is burning, until the heat penetrates and the wood can no longer support itself.

These two factors together determine heat transfer into the wood, how long it takes to ignite, and how quickly it will burn or fail, making size and moisture content the primary determinants of wood’s fire behavior.