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.
A relay should be preplanned to maximize the pump 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.
Any area that considers a tanker shuttle as a potential 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.
The most important considerations when pre-planning a maximum-distance relay is the appropriate available resource allocation. Will those resources make it to water? Knowing hydrant and drafting locations is invaluable, but knowing how far the available hose can go from that location is the important information. There is no substitution for walking with a wheeled measurer. This information should be pre-planned and easily available to the IC and crews. This distance information is timeless, since hydrant and static source locations rarely change. Don’t discount in-ground pools in the water pre-plan. An average in-ground pool may have more than 40,000 gallons of water, which can be very useful. When pools are the only source of water in an area, an open relay from pool to pool is a good strategic option. Pre-plan this tactic to include the appropriate adapters so the LDH refilling the primary drafting pool flows into a hard tube that has a reducer on the discharge side. This hard tube stops any hose kinking and reducing the tube size creates invaluable back pressure for the supplying pump.
The perceived difficulty of an LDH relay for a pump operator is usually isolated to one fact: a relay engine can expend most of its pump discharge pressure to propel the water to the next inline piece and the water may arrive under very little pressure. However, a quantity of water under very little pressure is still a quantity of water, and the next inline piece will reenergize and distribute that water. During relays, the International Fire Service Training Association suggests keeping 20 psi on the pumper’s intake gauge. This may not always be possible, but the concrete parameter will be cavitation which will obviously have an impact on the global fireground operation.
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 = Tank size – 10 percent divided by trip time
2,000 – 200 = 1,800 divided by 10 = 180 gpm
180 gpm x four tankers will provide a flow of 720 gpm
The last half of the arriving tankers maybe coming from quite a distance, leading to extended response time, exploiting the shuttle’s underlying weakness of drive/fill/dump time.
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 for appliance loss = 154.5 psi *
A 1,000-gpm pump will easily satisfy this 850-gpm relay’s pressure requirement. Two LDH engines in relay for just about a mile is more efficient than a four-tanker operation. The tanker operation would also require two additional pumps at the fill/dump site. In this hypothetical situation, an LDH relay allows a 66-percent reduction in resources and provides greater water flow faster and more dependably. As the distance from the fire to water increases, tanker shuttle efficiency is reduced and the LDH relay benefit increases. An LDH preplan with a list of the surrounding LDH resources, response area water locations, and the distances the LDH resources will reach from those identified water locations are integral to easily implementing an LDH relay. An LDH relay may be a superior strategic consideration, but only a thorough LDH preplan will allow the IC to make that determination.
Jeff Welle is a career paramedic, firefighter, and registered nurse. Web site: hydraulics4jakes.com
* Formula from from the Pump Operator’s Handbook, First Edition, Chapter 14, page 353.
