By Bruce Lake
照片作者,除非另有指示
While visiting family in Dunedin, Florida, I noticed that many buildings were marked with a small sign containing the letter “R” and or “F.” Upon closer inspection, I noted that the letters were inside a Maltese cross (see photo 1). My father in-law informed me that the signs were mandated by Florida law. Their purpose was to warn firefighters about the presence of “light-frame truss-type construction.” The letter “R” indicated roof and the letter “F” indicated floor. I thought to myself, “What a simple yet effective way to improve size-up.”
照片1.带字母“ R”的马耳他十字架标志汤姆·菲根（Tom Fidgen）的照片。
大小是消防员用来评估情况的信息收集过程。它根据准确的信息产生更好的决策的原则起作用。这是一个连续的过程，最初是在资源分配之前发生的。那么，用字母标记建筑物的规模如何改善尺寸？在我可以回答这个问题之前，您首先需要一些背景信息。
照片2.实木产品。
数十年来，工程木材产品（也称为轻量级结构）一直在取代传统或旧版材料。从历史上看，在地板和屋顶组件的建造中使用的材料由实木产品组成，例如2 x 8s，2 x 10s和2 x 12s（请参阅照片2）。工程设计的木材产品，例如I-ocist（请参阅照片3）和平行的和弦桁架（请参阅照片4），使建筑商能够在更短的时间内跨越更大的距离。在正常条件下，轻质材料与旧材料一样安全和坚固。但是，在火灾条件下lightweightmaterials will fail much quicker than solid wood products.
照片3.我 - 咖啡师。
Photo 4. Parallel cord trusses.
有关的：Tulsa Fire Department’s Bowstring Truss ID System|消防员的建筑问题：桁架|桁架屋顶大火，新泽西州威科夫|识别轻巧的结构
2008年，承销商实验室进行了实验，将工程木材的火力电阻特性与旧版材料进行了比较。在实验过程中，未受保护的遗产材料在倒塌前持续了18分钟。相比之下，仅四分钟后，未受保护的工程木材就失败了。在实验过程中，当将½英寸厚的通用石膏板放置在木材和火之间时，失败的时间增加到45分钟的旧式材料，轻量级25分钟。同样在2008年，加拿大国家研究委员会（NRCC）将工程木材的火力电阻特性与旧版材料进行了比较。根据NRCC的说法，在相同的火灾条件下，工程设计的木材产品将比实木托梁组件快35-60％。
Photo 4. Lightweight wood trusses.
这是非常具有挑战性的在最初的混乱a structure fire to determine whether or not a building contains lightweight materials. The only way to know for sure is good preplanning or to get inside and peel and peak. The presence of lightweight materials will have a significant impact on tactical decision making. Most incident commanders (ICs) will suspend roof operations once they know lightweight roof trusses (see photo 5) have been exposed to fire. Unlike legacy materials, the entire roof becomes unsafe and may potentially collapse if only a single lightweight roof truss has been damaged by fire. This is because of the additional stress placed on the remaining trusses.
Photo 6. Finished basement ceiling.
照片7.未完成的地下室天花板，带有传统地板桁架。Scott Lake的照片。
照片8.未完成的地下室天花板与I-toists。Scott Lake的照片。
During basement fires, ICs should not allow personnel to operate on the floor above the fire until the basement ceiling has been inspected. A finished basement (see photo 6) with uncompromised drywall on the ceiling is a good indicator of a safe floor above. If the basement ceiling unfinished (see photos 7 and 8), do not work on the floor above if the floor trusses have been damaged by fire.
传统上，消防员依靠警告信号来指示何时该从不安全的地板或屋顶退出。这些迹象包括感觉海绵状或明显下垂的表面。在处理轻量级构造时，不要依靠这些方法使您摆脱困境。轻量级材料将突然崩溃，而无需警告或时间做出反应。
Thermal imaging cameras (TICs) are not a reliable means of assessing floor stability above the fire. TICs only detect surface heat. The temperatures displayed will be significantly less than those impacting the trusses below. The differential is because of heat shielding and heat absorption by the materials between the TIC (i.e. sheathing and floor coverings) and the fire below.
For decades, the fire service has expressed concerns about the structural stability of lightweight construction materials under fire conditions. Research has proven that floors and roofs supported by lightweight materials will collapse at a much quicker rate than structures support by solid wood. Installing a small, tastefully designed sign or decal is a simple and inexpensive way to identify lightweight construction. Adopting this identification system would aid personnel in making safer tactical decisions on the fireground.
Bruce Lakeis a career fire officer and lieutenant with Halifax Regional Fire and Emergency in Nova Scotia, Canada. He is an accredited Level 4 Fire Officer, Level 3 Fire Service Instructor, Level 2 Firefighter, and Safety Officer. Bruce is a graduate of the fire service management program at Dalhousie University. He is a Blue Card Incident Command Instructor and Modern Fire Behaviorslice-rsinstructor. Bruce was also a contributor to the Canadian fire dynamics project,“从知识到实践。”在加入消防部门之前，他曾在加拿大军队担任步兵军官。
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