In fire conditions, rough cut timber lasts how long per inch of thickness?

In fire conditions, rough cut timber lasts how long per inch of thickness?

• A. 5 minutes per inch
• B. 10 minutes per inch
• C. 15 minutes per inch
• D. 2 minutes per inch

Answer: (A)

In fire conditions, wood’s resistance is largely governed by how fast it chars. A char layer forms on the surface and acts like an insulating shield, slowing heat from reaching the inner core. Because the heat has to penetrate through that char layer, the time a piece of rough cut timber can survive is roughly proportional to its thickness. The rule of thumb used here is about five minutes of exposure for each inch of thickness. So a piece that’s 2 inches thick would be around 10 minutes, 3 inches around 15 minutes, and so on. This estimate helps provide a quick, practical sense of how long rough cut timber might last under fire, though actual times vary with species, moisture, orientation, loading, and exposure conditions.

In fire conditions, wood’s resistance is largely governed by how fast it chars. A char layer forms on the surface and acts like an insulating shield, slowing heat from reaching the inner core. Because the heat has to penetrate through that char layer, the time a piece of rough cut timber can survive is roughly proportional to its thickness. The rule of thumb used here is about five minutes of exposure for each inch of thickness. So a piece that’s 2 inches thick would be around 10 minutes, 3 inches around 15 minutes, and so on. This estimate helps provide a quick, practical sense of how long rough cut timber might last under fire, though actual times vary with species, moisture, orientation, loading, and exposure conditions.