Water-Shuttle, Drafting and Relay-Pumping Operations

Introduction

Fire-service water supply is often limited not by the amount of water available in a region, but by the rate at which water can be collected, transported, elevated and delivered to the fire. Hydrants may be absent, damaged or inadequate; static sources may be distant; and a large incident may require a continuous flow greater than the municipal network can provide. Three operational systems address these conditions:

• Drafting, in which a pump draws water from a static source such as a pond, tank or swimming pool.
• Water-shuttle operations, in which tankers or tenders transport water between a fill site and a dump site near the incident.
• Relay pumping, in which two or more pumpers pass water through hose lines over distance.

These systems are not interchangeable. Drafting depends on pump suction conditions and source accessibility. Shuttles depend on vehicle cycle time, road conditions, filling and dumping arrangements. Relay pumping depends on hydraulic loss, pump capability, hose diameter, elevation and coordination. Effective incident planning combines hydraulic calculations with traffic management, crew safety and reliable command decisions.

Learning objectives

By the end of this chapter, the learner should be able to:

1. Assess static water sources and plan safe drafting operations.
2. Estimate tanker-shuttle capacity, cycle time and sustainable delivery rate.
3. Size a dump site and identify bottlenecks in filling and unloading.
4. Plan relay-pumping stages and determine approximate pump requirements.
5. Distinguish theoretical flow from sustainable operational flow.
6. Apply safety, environmental and command principles to water-supply operations.

1. Fundamental water-supply concepts

1.1 Required flow and available flow

The incident commander first establishes the required fire flow, usually from the fire-load assessment, number of attack lines, monitor demand, sprinkler demand and reserve requirements. The water-supply system must provide this flow continuously or for the planned operating period.

A useful planning distinction is:

• Required flow: the flow demanded by fire attack and exposure protection.
• Rated flow: the flow a pump, hose or appliance can deliver under stated conditions.
• Sustainable flow: the flow that can be maintained after allowing for filling delays, traffic, changing source levels, equipment failure and crew limitations.

The sustainable flow is normally lower than the sum of nameplate pump ratings.

1.2 Basic units and conversions

Fire-service calculations commonly use litres per minute (L/min), litres per second (L/s), cubic metres (m³), kilopascals (kPa), metres of water head (m) and kilometres per hour (km/h).

Useful conversions are:

• 1 m³ = 1,000 L
• 1 L/s = 60 L/min
• 1 bar ≈ 100 kPa
• 1 m of water head ≈ 9.81 kPa
• 1 km/h = 0.2778 m/s

The conversion between flow and volume is:

where Q is flow, V is volume and t is time. If Q is in L/min and V is in litres, t is in minutes. The equation assumes constant average flow during the interval.

2. Drafting from static water sources

2.1 Principle of drafting

A centrifugal fire pump does not normally “pull” water indefinitely. Atmospheric pressure pushes water up the hard suction hose toward the pump when the pump removes air and lowers pressure at the pump inlet. The maximum theoretical lift at sea level is approximately 10.3 m, but practical lift is much less because of vapour pressure, friction, air leakage, pump losses, water temperature and altitude. A planned lift of about 7.5 m or less is commonly preferred, subject to appliance instructions and local standards.

The pump must be primed, the suction line must be airtight, and the strainer must remain submerged. Air entering through a coupling, gasket, cracked hose or loose cap can interrupt drafting even when the source contains ample water.

2.2 Selecting and preparing a source

A source assessment should record:

• available volume and expected duration;
• depth, seasonal variation and access for appliances;
• distance from the pump to the water;
• slope and height difference;
• bank stability and vehicle load-bearing capacity;
• contamination, debris, ice or floating material;
• access for more than one appliance;
• environmental restrictions and permission requirements.

A source should contain sufficient water below the lowest expected operating level. The useful volume is not the total visible volume. It excludes unusable water below the strainer, sediment zones and water that cannot be reached without unsafe vehicle positioning.

2.3 Drafting arrangement

The preferred arrangement uses the shortest practical hard-suction path with gentle bends, a properly supported strainer and a strainer depth sufficient to prevent vortex formation. The strainer should not rest on the bottom, where it can draw sediment, nor be too near the surface, where it can draw air. A floating strainer may be useful where water level changes, but it must be secured against drifting into an unsafe position.

The pump should be positioned as close to the source as safely possible. Hard suction must be protected from vehicle movement, excessive bending and mechanical damage. Priming systems should be operated in accordance with the pump manufacturer’s instructions. Once drafting is established, the operator monitors vacuum, discharge pressure, engine condition, source level and signs of cavitation.

2.4 Hydraulic limits in drafting

The pump inlet pressure is affected by atmospheric pressure, elevation, suction lift and friction. A simplified energy relationship is:

where H_p is the pump head required, H_d is discharge pressure expressed as head, h_f is friction loss, h_e is elevation rise on the discharge side, and H_s is available static head at the source. This is a planning relationship rather than a substitute for the pump manufacturer’s performance curve.

As suction lift increases, the net positive suction head available to the pump decreases. Cavitation may occur when local pressure falls near the vapour pressure of water. Symptoms include a rattling sound, unstable pressure, vibration and reduced flow. The remedy is usually to reduce lift, shorten or enlarge the suction path, reduce pump demand, improve priming or relocate the appliance—not simply to increase engine speed.

2.5 Drafting safety

Personnel must avoid unstable banks, deep or contaminated water, moving water and unsupported ground. Exhaust gases must be directed away from crews and enclosed spaces. Strainers, ropes and hard suction must be handled without placing personnel between the appliance and the water edge. The source must be protected from fuel, foam concentrate and other contamination. Local environmental and water-use permissions must be followed.

3. Water-shuttle operations

3.1 System arrangement

A shuttle normally contains four functional points:

1. Fill site: water is transferred into tankers.
2. Travel route: loaded and empty vehicles move between sites.
3. Dump site: water is discharged into a portable tank, folding tank or other reservoir.
4. Attack pump: water is drafted or pumped from the dump site to the fire.

The dump site separates vehicle movement from fire attack and permits the attack pump to receive water while tankers are changing. A dump site should be established on firm, level ground with adequate lighting, drainage, traffic control and room for turning and staging.

3.2 Cycle time

For one tanker, the complete cycle includes filling, travel loaded, positioning and dumping, travel empty, and delays. A practical model is:

where T_c is cycle time, T_f is filling time, T_L is loaded travel time, T_d is dumping and positioning time, T_E is empty travel time, and T_w is waiting, queuing or miscellaneous delay. All terms must use the same time unit.

Travel time can be estimated from distance and average speed:

where d is one-way distance and v is average speed. Average speed must reflect intersections, congestion, road surface, turning and emergency-driving restrictions; the posted maximum speed is not automatically an operational average.

The theoretical shuttle delivery rate for n identical tankers is:

where Q_s is average delivery rate, n is the number of tankers, V is usable tank volume per tanker and T_c is cycle time. For mixed fleets:

The result is an average rate. It assumes the dump site and fill site can process all vehicles and that tankers do not lose usable volume through incomplete filling or reserve requirements.

3.3 Bottleneck analysis

The shuttle rate is limited by its slowest process. If the fill site has capacity Q_f, the dump site has capacity Q_d, and the tanker fleet has calculated capacity Q_t, then:

Here Q_attack is the rate that the attack system can accept, and Q_source is the rate that the source can provide. A safety and reliability allowance should be applied when conditions are uncertain. The minimum function prevents planners from claiming a delivery rate that another part of the system cannot support.

3.4 Dump-site capacity

A dump tank must hold enough water to maintain attack flow while the next tanker is arriving. A simple buffer requirement is:

where V_buffer is required buffer volume in litres, Q_a is attack flow in L/min, and T_g is the maximum expected gap between usable tanker discharges in minutes. The equation assumes the dump tank begins with sufficient water and that no additional inflow is available during the gap.

For example, if attack demand is 2,000 L/min and the maximum gap is 8 minutes:

This result is 266.7 L only if Q_a is expressed in L/s; with Q_a = 2,000 L/min, the correct calculation is:

Thus a minimum theoretical buffer is 16,000 L, before unusable volume, freeboard, reserve and operational margin are added. A common planning error is mixing L/min and L/s.

If a tanker delivers V_t litres and the attack consumes Q_a litres per minute, the net change during a cycle is:

For a stable operation, the average tanker supply must be at least equal to attack demand. If ∆V is negative for the fleet as a whole, the dump tank will eventually empty.

3.5 Worked shuttle example

An incident requires 1,800 L/min. Six tankers each carry 8,000 L. Each cycle consists of 6 min filling, 12 min loaded travel, 3 min dumping and positioning, 10 min empty travel, and 4 min delay.

The cycle time is:

Fleet delivery rate is:

Therefore the fleet cannot sustain 1,800 L/min. The shortfall is approximately 429 L/min. Possible solutions include adding tankers, reducing cycle time, increasing tanker capacity, establishing a closer fill site, or reducing the operational demand where tactically acceptable.

If eight identical tankers are used:

This slightly exceeds the nominal demand, but it provides little resilience. A road closure, incomplete fill or disabled vehicle could reduce the rate below demand; operational planners should normally provide reserve capacity rather than plan exactly at the threshold.

3.6 Fill-site design

The fill site must be designed for throughput rather than merely for access to water. Important features include multiple filling points where justified, a clear one-way circulation pattern, separation of entering and departing vehicles, pump capacity, hose protection, lighting and a staging area. The fill pump must not be operated beyond its safe source or engine limits. Tanker operators must verify tank status, close valves before movement and prevent hose whip or uncontrolled discharge.

4. Relay-pumping operations

4.1 Purpose and configuration

Relay pumping extends the useful range of a water supply by placing pumpers at intervals along a hose route. The first pumper receives water from a hydrant, static source or tender dump tank. Each subsequent pumper boosts pressure and supplies the next section. The final pumper supplies the attack operation or a manifold.

Relay planning must account for friction loss, elevation, appliance intake limits, hose diameter, pump performance and the possibility of a hose rupture. A relay is not simply a line of pumps operating at maximum throttle.

4.2 Friction and elevation

For a hose section, the required pump discharge pressure can be represented as:

where P_out is the pressure required at the upstream pump outlet, P_in is the desired pressure at the receiving pump inlet, P_f is friction loss, P_e is pressure associated with elevation rise, and P_r represents other required residuals or appliance losses. Pressure values must use consistent units.

The elevation component is approximately:

where ∆z is elevation rise in metres. A 10 m rise therefore requires approximately 98 kPa, before friction and other losses. A fall produces a pressure gain, but excessive pressure must still be controlled.

Friction loss depends strongly on flow and hose characteristics. In general, larger-diameter hose has substantially lower friction loss at the same flow. Exact calculations should use approved departmental tables, hydraulic software or manufacturer data for the specific hose, fittings and flow. Generic friction coefficients are unsafe when used without validation.

4.3 Relay spacing and number of pumpers

A relay section is acceptable when the upstream pump can supply the required flow at a pressure that is within its rated capability and the receiving pump obtains a safe positive intake pressure. If a route has length L and a selected hose section length l, the approximate number of hose sections is:

where ceil means round upward to the next whole section. This is a hose-count estimate, not automatically a pumper-count estimate. A pumper may supply one or more sections depending on hydraulic calculations and local operating procedures.

The number of pumping stages is determined by the pressure rise needed over the route and the allowable pressure per stage. In a simplified planning form:

where P_required includes friction, elevation and terminal pressure; P_source is pressure available at the first stage; and ∆P_stage,max is the usable pressure contribution per stage. The result must be rounded upward and checked against pump curves, intake pressure limits and hose working pressure. It is not a substitute for a complete relay plan.

4.4 Relay operating procedure

The relay should be built from the water source toward the fire, with radio communication established before charging the line. The final pumper is normally positioned first or the deployment is otherwise coordinated so that hose is not charged into an unprepared destination. Pumps are brought online progressively. Each receiving operator confirms adequate intake pressure before the upstream operator increases output.

Operators monitor discharge pressure, intake pressure, flow, engine temperature, hose movement and communications. Sudden loss of intake pressure may indicate a source problem, upstream pump failure, collapsed hose or excessive demand. Sudden discharge pressure rise may indicate a closed valve, blocked hose or downstream shutdown. The relay must be shut down in a controlled sequence to avoid damaging pressure transients.

4.5 Example of relay pressure planning

A relay must deliver 3,000 L/min to an attack pumper 600 m away. Approved hydraulic data indicate 70 kPa friction loss per 100 m of the selected hose at this flow. The route rises 15 m, and the attack pumper requires 500 kPa at its intake. Ignoring minor fitting losses initially:

Friction loss:

Elevation loss:

Required pressure at the start of the route is approximately:

Fitting losses, safety margin and pump intake requirements must then be added. The result shows why relay spacing cannot be selected by distance alone. The final design must verify that each pump and hose section remains within rated pressure and that the first source can provide 3,000 L/min continuously.

5. Comparing shuttle, drafting and relay systems

A shuttle can feed a relay or a dump-site pump. Drafting can supply a pumper that begins a relay. The systems should therefore be selected as an integrated water-supply architecture, not as isolated techniques.

6. Illustrative case study: industrial fire beyond hydrant range

Background

A fictional industrial fire occurs 2.5 km from the nearest hydrant. The fire requires 2,400 L/min for attack and exposure protection. A pond 300 m from the incident can support drafting, but the access road is narrow. A municipal reservoir 4 km away can fill tankers efficiently.

Problem

Incident command must provide continuous flow while avoiding congestion at the narrow pond access. A single pumper drafting from the pond cannot by itself deliver the required flow through the long hose route without relay support.

Analysis

A preliminary solution uses the pond as the dump-site source and establishes a relay from a drafting pumper near the pond. However, the narrow access allows only one tanker to approach at a time, making the pond unsuitable as a high-throughput fill site. The reservoir is selected as the fill site for shuttle tankers.

Assume ten tankers carry 10,000 L each. Their measured average cycle time, including filling, travel, dumping, return and delay, is 42 min:

This is slightly below the 2,400 L/min demand, so the plan has no useful reserve. Command adds one tanker:

A dump tank is selected with a usable working volume greater than the expected gap. If the worst measured gap is 7 min:

A tank with substantially more than 16,800 L nominal capacity is selected to allow freeboard, unusable volume and reserve.

A drafting pumper at the dump site supplies the first relay stage. Relay calculations using approved hose data determine the location of additional pumpers. Each stage is tested at the planned flow before attack lines are fully committed.

Approach and solution

The operation is divided into water-supply, fill-site, dump-site and relay groups. The fill officer records actual tanker fill times. The dump-site officer controls entry, discharge and departure. A dedicated pump operator monitors source level and intake pressure. Radio reports are made when tank level reaches predetermined trigger points, when a tanker is delayed and when relay pressure changes.

Outcome

The additional tanker provides a modest reserve, while the dump tank prevents short interruptions from immediately reaching the attack pump. The relay delivers the required flow after pressure testing. When one tanker experiences a mechanical delay, the buffer level falls but does not immediately interrupt attack operations.

Learning points

1. Nominal fleet capacity must be compared with measured cycle performance.
2. A small apparent surplus may be inadequate during a real incident.
3. Dump-tank capacity is a time buffer, not merely storage.
4. Relay spacing requires hydraulic data and elevation assessment.
5. Separate officers and clear communications reduce bottleneck risk.

7. Limitations, governance and contemporary practice

Calculations are only as reliable as their inputs. Travel speed may change, water levels may fall, pumps may derate, hose may be damaged and crews may become fatigued. Planners should use conservative measured values, conduct pre-incident surveys and record seasonal changes.

Water shuttle operations create road risk, noise, exhaust emissions and potential contamination. Agencies should comply with traffic law, occupational safety requirements, environmental permissions, equipment inspection rules and mutual-aid agreements. Tankers must not be overloaded, driven beyond safe conditions or positioned where their movement endangers attack crews.

Digital mapping, automatic vehicle location, pump telemetry and incident-management software can improve cycle-time measurement and identify approaching shortages. These technologies support—not replace—operator judgment. Artificial intelligence may assist with route prediction or resource allocation, but recommendations require human verification because emergency conditions can invalidate historical traffic and hydraulic assumptions.

Best practice includes pre-incident water-source surveys, standardized hose and pump data, tested shuttle routes, trained traffic controllers, spare equipment, written relay plans, redundant communications and post-incident performance review. After-action data should compare predicted and actual fill times, travel times, flow rates, pressure and interruptions. This creates a feedback loop for better future planning.

Chapter Summary

Drafting obtains water from a static source through an airtight suction system and depends on manageable lift, adequate submergence, reliable priming and avoidance of cavitation. Water shuttles move water between a fill site and a dump site; their sustainable delivery rate is governed by tanker volume, cycle time, fleet size and the capacities of the fill and dump systems. Dump-site storage provides a buffer against gaps in tanker arrival and must be calculated from attack flow and the maximum expected gap. Relay pumping extends water delivery over distance by staging pumpers and balancing friction loss, elevation, pressure and pump capability. The correct planning principle is to design for sustainable, measured performance rather than nameplate capacity. Safety, communications, environmental protection and regulatory compliance are essential parts of hydraulic planning.

Key Terms

Drafting: Pumping water from a static source through suction hose.

Static source: A pond, tank, pool or other stored body of water.

Suction lift: Vertical distance from the water surface to the pump inlet.

Cavitation: Formation and collapse of vapour bubbles caused by inadequate inlet pressure.

Strainer: Device fitted to suction hose to exclude debris.

Water shuttle: Coordinated movement of tankers between fill and dump sites.

Fill site: Location where tankers obtain water.

Dump site: Location where tankers discharge water for fire attack.

Cycle time: Total time for filling, travel, dumping and delay.

Sustainable flow: Flow maintainable under realistic operating conditions.

Buffer volume: Stored water available to cover supply interruptions.

Relay pumping: Sequential pumping through hose sections over distance.

Friction loss: Pressure loss caused by flow through hose, fittings and appliances.

Elevation loss: Pressure required to raise water through a vertical height.

Intake pressure: Pressure available at a receiving pump inlet.

Pump head: Energy per unit weight of water expressed as height or pressure.

Freeboard: Unfilled space retained to prevent overflow or unsafe movement.

Bottleneck: The process or component limiting total system output.

Hydraulic margin: Additional capacity retained above calculated demand.

Review Questions

Short Answer Questions

1. What are the three principal water-supply systems discussed in this chapter?
2. Why is practical drafting lift less than the theoretical atmospheric-pressure limit?
3. List the main components of a tanker cycle.
4. What is the purpose of a dump-tank buffer?
5. Why must relay pumpers maintain positive and adequate intake pressure?

Long Answer Questions

1. Explain the procedure for assessing and preparing a static water source for drafting.
2. Describe how a fill site and dump site should be organized for safe and efficient shuttle operations.
3. Explain the factors that determine sustainable shuttle delivery rate.
4. Discuss how friction loss and elevation affect relay-pumping design.
5. Compare drafting, water shuttle and relay pumping, including their advantages, limitations and appropriate applications.

Analytical / Application Questions

1. A fleet of seven tankers carries 9,000 L each and has a measured cycle time of thirty minutes. Calculate its average delivery rate in L/min and determine whether it can sustain an attack demand of 1,900 L/min.
2. An attack system consumes 2,200 L/min and the maximum tanker-arrival gap is 9 min. Calculate the theoretical minimum buffer volume, then explain why the selected tank should be larger.
3. A relay route is 800 m long, rises 20 m and has a measured friction loss of 60 kPa per 100 m at the planned flow. The terminal pumper requires 450 kPa. Calculate the approximate starting pressure before fitting losses and safety margin, and identify additional information needed for final design.

Multiple Choice Questions with Answers

Question 1

Which factor most directly limits practical drafting lift?

A. Atmospheric pressure only

B. Suction friction, air leakage and vapour-pressure effects

C. The colour of the suction hose

D. The number of attack lines alone

Correct Answer: B. Suction friction, air leakage and vapour-pressure effects

Question 2

A tanker carries 8,000 L and completes a cycle in 40 min. What is its average delivery rate?

A. 100 L/min

B. 160 L/min

C. 200 L/min

D. 320 L/min

Correct Answer: C. 200 L/min

Question 3

Which expression represents tanker-shuttle cycle time?

A. T_c = T_f + T_L + T_d + T_E + T_w

B. T_c = V × Q

C. T_c = Q/V

D. T_c = T_f − T_L − T_d

Correct Answer: A. T_c = T_f + T_L + T_d + T_E + T_w

Question 4

An attack flow is 1,500 L/min and the maximum supply gap is 6 min. What theoretical buffer is required?

A. 250 L

B. 1,500 L

C. 6,000 L

D. 9,000 L

Correct Answer: D. 9,000 L

Question 5

The sustainable shuttle rate is principally limited by which value?

A. The largest component capacity

B. The minimum capacity among source, fleet, sites and attack system

C. The tanker with the greatest engine power

D. The nominal capacity of the largest dump tank

Correct Answer: B. The minimum capacity among source, fleet, sites and attack system

Question 6

What is the approximate pressure increase required for a 10 m elevation rise?

A. 9.81 kPa

B. 49.1 kPa

C. 98.1 kPa

D. 981 kPa

Correct Answer: C. 98.1 kPa

Question 7

Why are relay pumpers positioned along a long hose route?

A. To reduce the amount of water needed at the fire

B. To overcome accumulated friction and elevation losses

C. To eliminate the need for hose testing

D. To replace all communication procedures

Correct Answer: B. To overcome accumulated friction and elevation losses

Question 8

If a tanker fleet supplies 1,371 L/min while demand is 1,800 L/min, what is the approximate shortfall?

A. 229 L/min

B. 371 L/min

C. 429 L/min

D. 3,171 L/min

Correct Answer: C. 429 L/min

Question 9

Which symptom is consistent with pump cavitation?

A. Stable pressure and silent operation

B. Rattling, vibration and unstable pressure

C. Increased tank volume

D. Lower road traffic

Correct Answer: B. Rattling, vibration and unstable pressure

Question 10

What should be verified before final relay-pumping design?

A. Only the colour of the appliances

B. Pump curves, hose friction data, elevation, intake limits and working pressures

C. Only the distance to the incident

D. Only the number of available drivers

Correct Answer: B. Pump curves, hose friction data, elevation, intake limits and working pressures