by Daniel P. Sheridan
While I was on medical leave recovering from surgery, I decided to start reading some things that I hadn’t looked at in awhile. I reread for the fifth time ChiefVincent Dunn‘s燃烧建筑物的崩溃, and when I was finished with that, I decided to tackle弗朗西斯·布兰尼根（Francis Brannigan）‘s消防服务崩溃. I finished them both. My first day back to the firehouse was a quiet Sunday. The day tour was very uneventful, with just a few runs. The night tour continued to be very quiet as well. At 0300 hours, the teleprinter in the battalion jumped to life, and the tones went off for the battalion to fill a 10-75 (working fire) in a commercial section of the borough.
I assumed that the fire was probably small. The sprinklers probably would have had the fire knocked down, I told myself, and we would not have a big problem. When we got into the car, however, I could tell by the tone of the first-due chief’s voice that this was not going to be the case. He asked for an extra engine and truck and wanted to make sure that the extra truck was a塔梯子. That is a great call: start getting the help there early. On the way there, my mind was racing because I had just spent the past few weeks reading Dunn and Brannigan.
I know the area where this fire was very well and that there are lots of truss roofs in that part of the city. The units on the scene were all engaged, and there wasn’t much information being put over the air. I was thinking that if the building had a bowstring truss roof, the guys may not have much time to make an interior attack. When we arrived, the fire was already in its advanced stages. The units were making a push in through the front, but they were confronted by an extremely heavy fire condition. We came in to the fire from the Exposure 2 (B) side and could see a wall of fire in the middle of the building. The fire building took up a quarter of a city block, approximately 250 × 250 square feet (about an acre). It was difficult to determine the type of roof system because of the heavy smoke condition, but because of the hips coming down on the front of the fire building, I was thinking it was a bowstring wood truss. In this case, a hip is a feature of a bowstring truss–the part of the roof that meets the wall in front. It is the part that slopes down in front and back. The bow usually spans the two sides (B and D); the hips come down the front and back.
The biggest problem with trusses is that the failure of one element may cause the entire truss to fail. According to Brannigan, bowstring truss construction is a compressive structure. Both the top and bottom chords are under compression. Trusses normally have the top chord in compression and the bottom chord under tension. “The economy of the truss is found in the fact that it separates compression and tension forces. However, this economy can also cause disaster. The bottom chord being under tension (like a rope) will precipitate failure. Conversely, the top chord being under compression responds like a column. The load-carrying capacity decreases as length is increased.”
除了一个沉重的火灾条件下,hydrant on the Exposure 2 side of the building went out of service at this fire, leaving the units on that side of the building without water. At this point, the chief in charge pulled everyone off the roof and conducted a roll call when he received a report from the roof that they had a gypsum roof. It was learned later that the roof was a steel bar joist truss roof (see photos.) Once the members were pulled off the roof, multiple alarms were transmitted, and the incident commander (IC) set up for a defensive operation.
钢为火增加了另一个动态。尽管钢是不可抑制的，但它仍然给火灾带来了一个巨大的问题，尤其是在暴露的情况下。钢的问题如下：
- Steel will begin to start elongating at about 1,000º F.
- If the steel is constrained and can’t elongate, it will push out whatever wall it is butting up against.
- Steel may fail when heated to temperatures of about 1,300º F. Cold drawn steel cables will fail at 800º F.
- 钢是一个良好的热导体，很容易传输热量。这意味着，如果您有可燃的屋顶，则可能会点燃屋顶材料。
Steel Elongates
Steel will expand from 0.06% to 0.07% in length for each 100º rise in temperature. The expansion rate increases as the temperature rises. Heated to 1,000º F, a steel member will expand 9½ inches for a section of steel 100 feet long. If the structure is able to restrain the beam, the floors will then become compromised. If the structure cannot contain the steel, in the case of one constructed of masonry, the wall will become compromised and will result in a catastrophic collapse.
Steel Fails
Today’s fire loads may be double what was expected in years past. With modern furnishings, it may be possible to achieve temperatures of 1,500º in five minutes. With this in mind, it seems that we may reach the failure rate for steel much faster in today’s fires. Like wood, steel also relies on its mass or weight. According to the standard fire test from National Fire Protection Association Standard 251,Standard Methods of Tests of Fire Endurance of Building Construction and Materials, the bar joists or lightweight steel truss will absorb heat rapidly and could fail in about seven minutes. Another point to consider is that the heavier the steel is loaded, the faster it will fail.
Steel Conducts Heat
An example that Brannigan uses is that a suit of armor is noncombustible, but no one would fight a fire in it. I have been to lots of duct fires in restaurants. Many times there are no major problems, and we are able to get some water into the duct and extinguish the fire. Other times, we have huge problems, such as when the ducts go through the walls of a five-story multiple dwelling or other types of buildings. There was a horrific fire in Paraguay, South America, a few years back. The fire started in the flue above a grill. The grill was used to cook lots of fatty meats, meaning grease had likely accumulated in the inside of the ductwork over time. The building used foam insulation as part of the roofing materials. I surmise that the grease ignited, resulting in the fact that heat from the fire conducted through the steel and ignited the foam. the heat from the fire conducting through the steel and igniting the foam? I believe more than 300 people were killed in that fire.
我们每天在美国，尤其是在快餐店或中餐馆中看到这一点。管道没有清洁，油脂会堆积，我们得到了很好的风管。问题是，如果钢管道几乎是可燃的任何东西，我们将有扩展。我曾经担心我的老房子里的烟囱。我有一个燃木炉，每隔一段时间我都会得到一场好的烟囱大火。杂酚油会堆积起来，然后当我散发出良好的火灾时，烟囱有时会起飞。我总是必须进入阁楼，并进行良好的检查。
According to Brannigan, with whom I am in total agreement, the heat or fire being generated is of secondary importance to the exposed steel. If water is applied to steel that is being exposed to high heat, the cooling effect of the water will draw the steel back to its original dimensions–in other words, at this fire, for example, it may be just as or even more important to get water on the exposed roof supports than the burning materials. In reality, it is possible to do both at the same time. If we aim our nozzles at the ceiling, we will be cooling the ceiling and extinguishing the fire at the same time.
EXPOSURE PROBLEMS
大概大约25年前，我们在一个仓库里开火，该仓库为纽约每日报纸的一些巨型报纸卷存储。卷将由铁路带入并装入一个巨大的仓库中。这个仓库的一部分位于纽约市主要桥梁的Triborough桥下。当时我被分配到塔楼。当时我还不明白这一点，但是回头看，负责的负责人在他的手中面临着巨大的挑战。当时还不了解太多，我认为最大的担忧是尝试节省尽可能多的仓库。我没有想到这座桥是更大的曝光问题。为了增加曝光问题，该建筑物位于城市的一部分，没有很多消防栓。多年来，我们在该地区遇到了垃圾大火，我们需要发出第二次警报以进行水继电器。
这座桥是此操作中的主要曝光。我们将塔梯子靠近桥设置为。大火后，当我们回到宿舍时，卡车上的每盏灯都融化了。
几年前，在纽约州立大学的繁忙地区，在地下通道下发生了一场汽油油轮大火。由于大火，由于火灾损坏，通道被关闭了一段时间。钢不可抗化的事实是无关紧要的 - 它仍然会失败或传播热量。我们需要确定什么是燃烧以及我们的结构在每个操作中都能成功和安全。
