By Jeff Welle
Tankers are an important part of fire department strategy and sometimes the only option to provide water supply. Without exception, every tanker shuttle shares the same basic characteristics of an large diameter hose (LDH) relay. Both operations need a pump at the water source and a pump at the distribution point, however, the LDH relay is always considerably more efficient. The efficiency issue becomes more prominent as the distance from water to fire becomes greater. Also, this efficiency advantage is attained with fewer required resources. Multiple tankers are required for even a moderately successful water flow, and very rarely will a tanker shuttle provide an uninterrupted water supply. The resources required for a tanker shuttle are a complicated logistical problem, including available tankers and their load, fill/drive/dump time, bridge and road limitations, and weather considerations. Multiple vehicles are required from multiple agencies, resulting in increased response time prior to establishing an effective water supply. This time delay and the inherent complication of multiple agencies responding and operating can justify consideration of a maximum distance LDH relay.
继电器应预先计划的最大化and hoseload potential of an apparatus. The preplan must consider required gpm flow (as roughly determined by the National Fire Academy (NFA) or Iowa State University formulas), maximum length of hose, and the fact that the pumper at the water source cannot exceed 185 psi (maximum pressure). An average engine setup may have 1,500 feet of LDH; dropping miles of hose at 1,500-foot intervals, and eventually picking up that hose presents a logistical problem in itself and may lead the incident commander (IC) to select the more straightforward tanker shuttle option as the strategic water supply. However, with a maximum distance relay preplan and a few LDH-specific engines, a continuous respectable water supply can be established with far fewer resources and with considerably fewer logistical considerations.
任何领域,认为一艘油轮航天飞机的种种折磨ntial strategic water supply will have tankers in almost every surrounding station. I’m not suggesting replacing those tankers, which are invaluable resources. However, if tankers are routinely used, maximum distance LDH engines may be a viable strategic consideration. Pump capacity of the potential LDH vehicle is a secondary consideration to the size of the vehicle’s hosebed. The LDH maximum operating pressure is 185 psi; at that pressure, the pump won’t produce more than roughly 80-percent capacity, and 80-percent capacity of even a 1,000-gpm pump will meet an LDH relay’s needs. A reserve engine may be a good candidate to fulfill this role, once again, depending on hosebed capacity. An LDH relay engine is set up to flow from between 500 and 750 gpm at its longest distance. A 2,000-gpm, two-stage pump run in series will obviously meet the required flow rate, but more importantly will have the pressure ability to capitalize on the LDH maximum operating pressure. Two LDH engines with 3,000 feet of five-inch hose on each engine can drop more than a mile of hose in less than 10 minutes. It takes another three to five minutes to set up the hose/hydrant/draft and a 750-gpm water supply is established more than a mile away for the duration of the fire with only one engine in relay. This relay can potentially go on for miles until the IC has exhausted the available LDH vehicles in the preplan. If the IC has to call for additional resources, perhaps the mutual aid call could be for an organized hose relay instead of tankers.
预先计划最大距离继电器的最重要考虑因素是适当的可用资源分配。这些资源会倒水吗？了解消防栓和起草地点是无价的，但是知道可用的软管与该位置可以走多远是重要的信息。与轮式测量室无可替代。此信息应预先计划，并易于提供给IC和机组人员。此距离信息是永恒的，因为消防栓和静态源位置很少发生变化。不要打折水预计划中的地面池。平均地面池可能有40,000加仑的水，这可能非常有用。当游泳池是某个地区的唯一水源时，从游泳池到泳池的开放继电器是一个不错的战略选择。预计划了此策略，以包括适当的适配器，因此LDH将主要的绘图池的重新填充到一个硬管中，该硬管在放电侧有还原器。 This hard tube stops any hose kinking and reducing the tube size creates invaluable back pressure for the supplying pump.
LDH继电器对泵操作员的感知难度通常是一个事实：继电器发动机可以花费大部分的泵放电压力，以将水推到下一条直列，而水可能在很少的压力下到达。但是，在很少的压力下，大量的水仍然是一定数量的水，而下一件直列的碎片将重新加入并分配水。在接力赛中，国际消防培训协会建议将20 psi保留在浮力器的进气口上。这可能并不总是可能的，但是混凝土参数将是空化，显然会对全球火灾的操作产生影响。
Shuttle efficiency is based on an individual tanker’s dump/fill piping, tank size, handling time, and travel time. These individual variables make it difficult to identify a specific shuttle’s exact efficiency. Let’s imagine a hypothetical situation: There is a structure fire in a rural area with the closest water just about one mile away from the fire. This rural area has fire stations 15 miles apart, and each station has a 2,000-gallon tanker. After responding, each tanker could be expected to do a round trip in about 10 minutes.
gpm =坦克尺寸 - 10％除以旅行时间
2,000 - 200 = 1,800除以10 = 180 gpm
180 gpm x four tankers will provide a flow of 720 gpm
到达的油轮的后半部分可能来自很远的距离，导致了延长的响应时间，从而利用了航天飞机的驱动器/填充/垃圾时间的潜在弱点。
However, if the two closest stations each had an LDH engine with a 1,000-gpm pump and 2,500 feet of five-inch hose, only two apparatus would be required for this hypothetical relay. Five thousand feet of five-inch can be dropped and operational in about 10 minutes. The LDH relay would require fewer resources (apparatus and firefighters), provide a greater flow of uninterrupted water, and be fully operational in much less time when compared to a tanker shuttle. The target flow for this 5,000-foot, two-engine LDH relay is 850 gpm.
.08 x 8.5 x 8.5 x 25 = 144.5 psi + 10 psi用于设备损耗= 154.5 psi *
1,000升 /加仑的泵将很容易满足850-750-PM接力的压力需求。接力中的两个LDH发动机仅比四阵操作更有效。油轮操作还需要在填充/转储站点上附加两个泵。在这种假设的情况下，LDH继电器可减少66％的资源，并更快，更可靠地提供更大的水流。随着火灾到水增加的距离，油轮穿梭效率降低，LDH继电器益处增加。LDH的Preplan具有周围LDH资源，响应区域水位的列表，以及LDH资源将与确定的水位置相关的距离，是轻松实施LDH继电器的组成部分。LDH继电器可能是卓越的战略考虑，但是只有彻底的LDH Preplan才能使IC做出确定。
Jeff Welle is a career paramedic, firefighter, and registered nurse. Web site:hydraulics4jakes.com
*公式来自泵操作员手册，第一版，第14章，第353页。
