Hacker News Reader

Comment by jseliger | Hacker News Reader

although is burns

The article also notes that this kind of wood is "fire resistant." It also says that, "But the road to approve CLT as a sound building material in the US has been arduous, with engineers and architects working to prove that it complies with codes and is resistant to fire and seismic events." Despite that, though, it still seems like fire is a threat. Is there something I'm missing? Are the other materials in the buildings sufficiently fire-retardant to make the issue a small or unimportant one?

View on HN

When you set a large beam of wood on fire, what typically happens is the outside chars but the fire never reaches the core, which stays intact. This won't happen so much with typical dimensional lumber like a 2x4, but when you look at timber framing using 5x5 or 5x10 beams as a stock element, the effect can be quite real.

Fire is always a threat. The question is how fast the burning spreads and the structural capacity during a burn. Fire retardants which are pressured into the wood, begin to react when the temperature approaches normal wood burning points (around 275 C) the chemicals convert the wood tars to a carbon char which provides insulation from direct heat while also allowing the water to evaporate out of the wood as it more slowly heats. This gives you a much longer horizon to get people out and firetrucks in. You would need a sustained burn for a couple hours, at which point an exposed steel building would have fallen anyway.

A typical high rise building will experience some small fires during its lifetime that aren't structurally threatening. Is the wood building going to require more repairs or inspections in these cases?

There would have to be extended contact (more than just a small kitchen fire). Usually the beam will be repaired or replaced anyway because of aesthetic reasons, and much of the wood structure will be behind fireproofing where it's 100% safe for at least a couple hours.

Reply on news.ycombinator.com