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"Using wood means greater fire safety" Edit: Outside of how ridiculous this statement is, how does one bring a charred wooden high-rise back up to code?!
by ynniv 8y ago
"Using wood means greater fire safety"
Edit: Outside of how ridiculous this statement is, how does one bring a charred wooden high-rise back up to code?!
- supermw 8y agoWhat is burnt may never burn. See Shou Sugi Ban (焼杉板).
- benj111 8y agoCharcoal? Coke?
- vidarh 8y agoProduction of charcoal and coke both depend on not fully burning the wood or coal, by constraining the oxygen supply, but by heating/baking it to reduce the water content and volatiles. Older processes burn more of the material, in part to help produce the heat, while newer processes try to fuel it mostly of the off-gassing. But the comment above is referring to a specific treatment of wood by charring the outer layer to make it act as a fire retardant.
- benj111 8y agoMy understanding of Shou Sugi Ban is basically to create a charcoal layer on the wood, so its unclear to me how that would prevent it burning, as charcoal is designed to burn. At best I can see it increasing the ignition temperature.
- chipsa 8y agoIt's not fully charcoal (fully carbonized). Wood is mostly two compounds: cellulose and lignin. They undergo thermal decomposition at different temperatures. By partially burning the exterior, you decompose the cellulose, and when you attempt to set it on fire again, it's harder to light, because you no longer have the cellulose decomposition to provide fuel, but have to get to a higher temperature for the lignin to decompose. It's charred, but not charcoal. And yes, mostly it just makes the ignition temperature go up. But that's half the battle for fireproofing. You're mostly not trying to stop it from ever burning, but giving people enough time to evacuate, or the firefighters to put it out with water.
- aaronblohowiak 8y agosteel gets floppy before it gets melty. Wood stays rigid as it burns until it snaps. Many factors when thinking about which is better.
- burfog 8y agoBuild the structure with steel pipe. Fill it with water. The temperature can not exceed the boiling point of water until all of the water has been boiled away.
- pjc50 8y agoSteam expands, so you're going to have some nasty pipe explosions in there. Also you'd need a way to stop the water corroding it from the inside.
- burfog 8y agoNo, the steam comes out. The water won't boil if it is contained under pressure, and it must boil in order to keep the temperature down. Dirty water and a bad choice of steel will lead to corrosion, so don't use those. Purify the water and/or use a different type of steel.
- deleted 8y ago[deleted]
- stmfreak 8y agoYea, I went looking for the same thing. I find it misleading to claim that steel melts in high rise fires and collapses (only three times in history) but wood chars and becomes fire resistant (at same temperature to melt steel??). I would never choose to live or work in a multi-Tennant hi-rise due to fire risk.
- aaronblohowiak 8y agoYou don’t have to get anywhere near melting temp to weaken the beam strength of steel. From the internet: Average building fires reach temperatures of 700 to 1000°C. Steel weakens dramatically as its temperature climbs above 230°C, retaining only 10 percent of its strength at 750°C. Wood generally does not ignite until it reaches 250°C. Once it catches fire, wood develops a protective insulating char layer. After 30 minutes a large wooden beam will have lost around 25 percent of its strength in a 750°C fire and retain structural integrity – a steel beam will have lost 90 percent strength and will have failed.
- umvi 8y agoBut what is actually burning in a steel and concrete structure? Drywall and carpet?
- burfog 8y agoUsually nothing, because this pretty much doesn't happen. It is nearly correct to say that steel buildings never burn down. The last exception to this rule involved luggage, seats, and lots of jet fuel.
- macawfish 8y agoSome guesses: furniture, bedding, appliances, clothes, papers, trim, flooring, paint, etc.
- sundvor 8y agoCombustible cladding. https://www.theage.com.au/politics/victoria/smoke-alarm-warning-with-no-sign-of-fix-to-melbourne-s-cladding-crisis-20190215-p50y6j.html https://www.theage.com.au/politics/victoria/smoke-alarm-warn... https://www.theguardian.com/uk-news/2018/jun/18/fire-safety-rules-rely-solely-on-staying-put-grenfell-inquiry-ladders https://www.theguardian.com/uk-news/2018/jun/18/fire-safety-...
- war1025 8y agoThere was an article some time back about fire ladders and how wooden ones will still be structurally sound after getting quite burnt, while metal ones can lose their integrity well below temperatures where the metal would actually melt. I think it was in relation to the San Francisco fire department.
- blahedo 8y agoThis one? https://gizmodo.com/inside-san-francisos-fire-department-where-ladders-are-1552279252 https://gizmodo.com/inside-san-francisos-fire-department-whe...
- war1025 8y agoyup. that's the one
- FireBeyond 8y agoSFFD uses wooden ladders due to overhead power lines, predominantly.
- newnewpdro 8y agoThe I-beams used in modern highrise construction are a world different from lightweight aluminum extrusions used in ladders. Aluminum is one of the butter metals.
- jdsully 8y agoI beams are quite safe if the fire retardant remains on (a major cause of the WTC collapse was the fire retardant getting blown off by the impact). Trusses on the other hand are quite dangerous in a fire. https://community.fireengineering.com/forum/topic/show?commentId=1219672%3AComment%3A8027&groupId=1219672%3AGroup%3A2423&id=1219672%3ATopic%3A3615 https://community.fireengineering.com/forum/topic/show?comme...
- newnewpdro 8y ago
- vegardx 8y agoFor the same reason you won't be starting your bonfire with the big logs. It has a huge thermal mass and it takes a lot of external energy to make the fire self-sufficient. It's also easier to repair, as you can just replace the damaged wood. With concrete that's not so easy, and in some cases it can be hard to even gauge how damaged concrete is from fire damage.
- jlg23 8y agoAccording to this study, it does not compare too bad: https://www.firechief.com/2017/03/14/are-wood-frame-high-rises-a-fire-risk/ https://www.firechief.com/2017/03/14/are-wood-frame-high-ris...
- ynniv 8y agoThanks, this is a good summary of something I wasn't paying attention to. It contains an interesting point: The standard of workmanship (particularly in the installation of plasterboard or sheetrock) is a critical component to the necessary fire resistance
- mauvehaus 8y agoWent to a talk about this (among other things). Short answer: They size the structural members making an allowance on depth from the surface for char (zero strength) and a further depth of affected material assumed to be weakened. The unaffected wood inside is what supports the structure. For a dramatic demonstration of how shallow a fire actually penetrates wood over a short period of time and how well it insulates, see here: https://www.youtube.com/watch?v=YU48ypPTH1E https://www.youtube.com/watch?v=YU48ypPTH1E (Promotional, but informative nonetheless)