屋顶操作：轻巧的桁架和变化
BY BOB PRESSLER
In “Ventilating Flat Roofs” (September 1996), I discussed basic roof operations for a first-due truck company in buildings primarily of ordinary construction with flat roofs, skylights, and scuttle covers. Different construction components have a direct impact on our operations. The first personnel on the roof must recognize unusual roof features and relay such information to the incident commander. The IC in turn will determine the feasibility of roof operations and committing additional resources to this position.
LIGHTWEIGHT STEEL BAR JOIST TRUSS
您可能会遇到的最常见的屋顶之一是钢制梁式桁架组件，上面覆盖有瓦楞金属屋顶，通常称为“ Q”甲板。金属杆托梁可用于跨越大于50英尺的距离，通常发现间距四到六英尺（可以根据整个屋顶的设计方式，可以更大的间距）。这些屋顶组件缺乏防火性，几乎没有或根本没有保护力的保护力。屋顶的评级来自安装的屋顶覆盖物的类型以及安装在屋顶下方的天花板瓷砖的类型。不要依靠轻质的钢桁架来承受任何大量的火力。
覆盖你通常会发现在这个屋顶a metal decking covered with a combination of hot asphalt, which is covered with tar paper; a rigid insulation approximately one to two inches thick; and a built-up roof of paper, tar, and gravel. One hazard associated with the metal decking is that the sheets are installed in a staggered pattern. The joints and seams do not necessarily end at supporting beams; most times, they do not. This leaves the possibility of an unsupported “flap” left after you`ve cut a ventilation hole.
Another type of roof decking found with trusses is gypsum decking. There are two main types of gypsum roofs. One is installed using gypsum planks usually two inches thick and two feet wide by eight feet long. The other is poured in place on form boards with reinforcing wire added for strength. Both types are covered with a waterproof roofing material.
With its tar and gravel covering, this type of roof may be hard to identify. A telltale sign of gypsum roof decking is that once you start to cut it with a power saw, a cloud of dust will be thrown from the saw and a powdery residue will be left. Because both forms of gypsum are very heavy and supported by a truss roof assembly, anticipate early collapse and do not attempt operations under heavy fire conditions.1
The trusses` underside may be covered or left open. In office buildings or shopping malls, ceiling tiles will normally be installed in all business and sales areas. Some areas, such as storage, utility, and staff locker rooms, may not have tiles. In large commercial buildings, such as light manufacturing occupancies, garages, and storage facilities, only the front reception area might have tiles. In most cases, the tiles are suspended on a grid of lightweight metal framework, which is hung from the trusses with wire. Entire grids have been known to fail during a fire, dropping down in large sections, ensnaring anyone below.
您必须尽早在可能的时刻（如果有的话）对建筑物进行屋顶操作。一流的卡车官员，或IC如果他先是第一次到达，则必须尝试确定消防的位置和严重性。如果烟雾或热量状况表明了先进的火灾状况，则在射击主体上进行操作并不安全。仅几分钟暴露于高温条件后，这些桁架就会开始失败。如果仅显示轻烟或有轻度火灾状况，则可以执行屋顶操作。同样，这是一个基于生命危害的判断电话，包括消防员和被困的乘员和火灾条件。
If the IC decides to send firefighters to the roof, they should perform operations quickly and then withdraw to an area of safety. In large buildings, this may involve their moving to another section or simply backing up so many feet.
As with buildings of ordinary construction, first look for any natural openings that you can use for rapid ventilation. In large buildings, you may find skylights. Luckily for us, skylights are made of plastic and will self-vent if they are near the main body of fire. If there are no outward indications of fire, look for smoke pushing near these skylights or smoke inside the skylights. Remember that randomly removing the skylights may spread the fire.
Look for any ventilators or ductwork that may terminate at roof level. They may offer clues as to where the main body of fire is located. Remove turbine-style ventilators at serious fires, even if they are remote from the main body of fire. The way they are designed to alleviate heat from the cockloft or attic areas will also rapidly spread the fire: The more heat that builds up, the faster the turbine spins and the more air it moves.
If there are no skylights or if they are not in an advantageous position, you may have to cut the roof itself. You can cut the roof decking with a carbide-tip blade, but a metal cutting blade works best. The first cut will normally not go deep enough to cut the entire metal decking, but it will make it possible to remove the roof covering. You will need a second cut inside the original cut, by three to four inches, so that the guard will not get hung up on the built-up roof.
由于矩形切割可能会使锯操作员站在无支撑的金属甲板上，因此一些公司正在尝试在金属屋顶上进行大型三角形切割。尽管开口的大小减少了，但您将获得更快的操作（四英尺平方孔的总切割16英尺，而12英尺，四英尺乘4英尺乘4英尺四英尺的三角形）以及不受支持的屋顶部分的稳定性。
Depending on the size of the roof and the extent of the fire, it may be necessary to leave the roof as soon as you complete your cuts. On a large roof, it may be possible to retreat and start another hole. Take care, as the fire may be spreading rapidly below your feet. Fires in buildings with this type of roof have been known to spread in the valleys of the corrugated metal roofing. The heat of the fire turns the hot asphalt covering back to liquid, which produces flammable gases that then ignite. The fire spreads along the valleys of the “Q” decking, heating more asphalt as it goes. This may occur a fair distance from the original fire area. There are two ways to fight these deck fires: from above by cutting the roof (potentially with a trench) or from below by using hose streams to cool the underside of the deck, stopping the gas production.
Remember, these roofs will rapidly fail under advanced fire conditions. If there are any signs to indicate that it is a fast-moving fire or that the building`s integrity is in doubt, do not commit personnel to a building with these trusses.
OTHER LIGHTWEIGHT VARIATIONS
The wood products industry has also introduced several products that greatly impact the fire service. Lightweight wooden trusses are used both as roof and floor assemblies. Once a building is enclosed, it is almost impossible to determine what it was constructed of. That is why you must keep apprised of what is going on in your district.
轻巧的木桁架通常由2 2 4木材组成，用于屋顶和地板组件。这些与帮派指甲或毛刺板一起固定在一起。尽管帮派指甲应渗透到大约一半英寸的深度，但存在变化，包括那些仅到四分之一英寸的人。这些桁架通常用于24英寸的中心间距。然后，屋顶可以用胶合板或片状板覆盖。根据屋顶甲板的厚度，开始在屋顶上工作的人员可能会发现它感觉有些海绵。
As with fire operations in buildings with lightweight steel trusses, you must perform operations on these roofs early in the fire. The IC must anticipate the need for vertical ventilation and assign personnel early. If the IC waits until the fire has extended into the attic area, it may be too late to assemble the needed firefighters, raise ladders, and begin ventilation cuts–the fire will already be attacking the truss components. Under heavy fire conditions, anticipate early truss failure. Dead load storage in the attic area, gang nails that may have loosened in transit or installation, and the added weight of clay tile or second or third roofs can all contribute to early truss failure.
When the trusses are used as floor assemblies, the collapse potential is just as great. An additional problem is the fact that this truss void is protected by gypsum board below and covered by plywood above. Both act as insulators and may hide the fact that the fire has entered this loft area. The fire now has the run of this entire area. The only vertical obstacles to horizontal fire spread are draftstopping if it has been installed properly or the four outside walls. Fire can burn unchecked through the void area, reach the outside wall, and spread to the upper levels–all the time being shielded from firefighters by the walls. That is why even at relatively minor room and contents fires in drywall buildings it is important to check for extension.
消防人员的生命由石膏板保持平衡。正确安装，它将给我们提供相当多的防火性。这是没有任何不适当的开口。管道，电气服务和管道运行只是可能穿透干墙的一些服务。如果开口未正确密封，则火和烟雾有一条遵循的路径。从建筑物的外观中，IC必须观察消防大楼地板之间的区域。从该区域推出的烟雾可能意味着空隙中的火。
Wooden I-beams are also gaining in popularity. They are used to span large distances, up to 60 feet, and can be found in all types of structures. In live fire tests of an unprotected floor assembly, they performed very poorly, failing in around five minutes.2 So again, we will be basing our survival on the drywall.
Most of the lightweight wood trusses use plywood as the final external layer, whether as flooring or as roof decking. Its use as roof decking makes the process of opening up these roofs with power saws relatively easy. To make cuts and get off the roof as soon as possible, I recommend the louver cut. Not only does it work well with the plywood, but it is less time-consuming to just “flip” the cuts vs. trying to pull the sections.
Other new ideas for the construction trade include metal “C” channels used as both rafters and beams. They are similar to the galvanized studs that are frequently used, but they are of a much heavier gauge. There has not been much documented experience with them under fire conditions, but expect them to perform just as other unprotected metal components–early failure.
It is in your best interest to be aware of what goes on in industries that affect the fire service. It is also important to know what buildings are going up in your district. Once they are on fire, it is too late to try to guess what is holding the building up. n
尾注
1. FDNY安全消息90。
2. Brannigan, Francis L. Building Construction for the Fire Service, Third Edition (Quincy, Mass.: National Fire Protection Association, 1992), 541.
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A lightweight open web steel bar joist building with corrugated metal decking. This assembly as shown has no fire rating. The rating comes from the ceiling and roof that are used. (Photos by author unless otherwise noted.)
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Roof turbines are visible along the roof line of this multiunit apartment complex. If fire enters the attic area, a rise in temperature will cause the turbines to spin faster, spreading the fire. Remove all turbines to avoid this.
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(左)泰pical built-up roof on metal decking consisting of multilayers of material: two layers of tar and gravel with insulation in between, about three inches thick. (Photo by Tim Melton.) (Right) A triangle-shaped vent hole is cut in a metal decking roof. The triangular shape seems to reduce the flap problem. This roof needed to have the covering, about three inches worth, removed before the deck could be cut. A chain saw was used to cut this material. Then a rotary saw with a metal cutting blade was used to finish the opening. Remember to cut inside the original dimensions of the hole (about three inches) so that the handles or guards on the saw do not prevent the blade from reaching proper depth. (Photo by Tim Melton.)
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(Left) All new townhouse construction featuring lightweight wood roof trusses, floor trusses, and metal studs. In some cases, the metal studs are nonfirestopped, giving a channel for smoke and heat to spread unchecked throughout the building if the fire breaks through the drywall skin. (Right) Closeup of a typical gang nail. Notice how the bottom chords do not line up perfectly and how regular nails are used to secure the plate.
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(Left) Smoke pushes from two of those “in between” areas. At the line between the first- and second- floor windows–at what should be floor level–smoke is pushing through the siding; at the upper righthand exposure 4 side, smoke is pushing from the area where the two buildings meet. Both are indicators that the fire has developed from a room and contents fire; has gotten through the protective skin (drywall or plaster); and is now in the voids of the building, attacking the structural components. (Right) “C” channels, heavy gauge metal in the shape of a capital “C,” are installed as roof rafters in this modern church. They get their lateral strength from the plywood decking. Like most steel structural components, these channels are susceptible to elongation, twisting, and early failure under heavy fire conditions.
鲍勃·普拉斯勒（Bob Pressler）是消防局22年的资深人士，是纽约市（纽约）消防局3号救援公司的消防员。他为消防工程视频系列“面包和黄油”操作创建并制作了视频峰值通风和SCBA安全和紧急程序。188金宝搏是正规吗Pressler拥有俄克拉荷马州立大学的消防工程副学士学位，是一位经常在各种消防主题上的讲师，并且是志愿者部门的成员。
