| 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
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