NFPA D/O Mobile Water Supply cheat sheet

Pre-trip walk-around covers tires and tread depth, wheel lug torque, brake adjustment stroke, lights, siren, air pressure build-up and leak-down rates, fluid levels, and pump engagement.

NFPA 1901/1911-style daily/weekly checks: pump shift in and out of road and pump gear, transfer valve operation, tank-to-pump valve, dump valve and chute, primer, relief valve, and gauges zeroed.

Tank water is a perishable commodity: record fill date and source; drain, flush, and sanitize on a scheduled cycle and after any suspect source to control biological growth.

Tire and axle loading: verify scale weights against GAWR and GVWR; a full water tank plus hose load frequently pushes rear axles to or beyond rating if not weighed loaded.

Brake system checks include slack adjuster pushrod travel within limit, low-air warning at approximately 55-60 psi, and governor cut-in/cut-out near 100/120-125 psi.

Annual service test of the pump at rated capacity, plus a hose and appliance inventory audit, confirms the apparatus can deliver its rated flow when needed.

Out-of-service criteria: inoperable dump valve, failed pump shift, unrepaired air leak, or expired hydrostatic test on any pressure vessel or SCBA cylinder removes the unit from water supply duty.

Document every discrepancy with date, mileage/hours, and corrective action; readiness is a maintenance record, not a verbal claim.

Defensive driving rule: maintain a following distance of at least four seconds in good conditions, increasing with speed, load, and road surface; a loaded tanker needs far more stopping distance than a passenger car.

Liquid surge is the dominant handling hazard: baffles reduce but do not eliminate movement; brake and accelerate smoothly, and enter curves below the posted advisory speed.

Rollover risk rises with a high center of gravity and partial fills; a partially loaded tank produces the worst free-surface effect, so travel with a full or empty tank when practical.

Emergency vehicle operation is governed by state law and department policy: due regard for safety, sirens and lights when required, and full stop and confirmation before proceeding against a red signal.

Right-of-way is requested, not taken; clear each intersection lane by lane and never assume other drivers hear or see the apparatus.

Downhill braking uses engine or retarder braking with controlled service brake application; sustained light braking overheats drums and fades the brakes.

Backing requires a spotter at the rear with eye contact maintained; if visual contact is lost, stop immediately. Use a guide for dump site positioning.

Load and route planning: verify bridge weight postings, overhead clearances, and soft-shoulder conditions before committing a heavy, high-profile water tender to an access road.

Flow equation: Q (gpm) = 29.7 x d squared x square root of nozzle pressure (psi), where d is nozzle diameter in inches; for a smooth bore tip.

Friction loss: FL = C x Q squared x L, with C per 100 ft of hose (1.75-inch, 2.5-inch, 3-inch, 4-inch values differ) and Q in hundreds of gpm; L is length in hundreds of feet.

Engine pressure: EP = NP + FL + elevation change (0.5 psi per foot of rise, subtract for drop) + appliance loss.

Available flow from a static source is limited by the source's ability to replenish; a draft operation can only sustain what the water table or hydrant can deliver.

Required fire flow estimates follow the NFA formula: needed gpm = (length x width / 3) x percent involvement x 100 for a single-story building.

Water weighs 8.34 lb per gallon; a 2,000-gallon tank adds about 16,680 lb, and 1 psi equals 2.31 feet of head.

Relay and shuttle capacity calculations must use the sustained rate of the weakest link, not the pump's rated capacity.

Drafting lift is practically limited; at sea level a lift beyond about 20-25 feet becomes unreliable, and altitude reduces the achievable lift.

Tank capacity classes commonly range from 1,000 to 5,000 gallons; NFPA 1901 sets minimum tank size, pump capacity, and tank-to-pump flow rates for apparatus designated as water tenders.

A dump valve sized for rapid unloading (often 8-10 inch or larger) with an extension chute and a controllable opening rate prevents a violent dump that can damage the tank or the receiving basin.

Baffles divide the tank into compartments to limit surge; baffle condition, welds, and venting are inspection points because a failed baffle concentrates liquid momentum.

Pump options include front-mount PTO, midship, and rear-mount; a rear-mount pump with a large suction intake supports fast fill and dump cycles.

Jet or educator fill systems can load a tanker in about a minute at high flow, but require a pressurized water source and a properly sized vent on the tank.

Tank venting must allow air to escape during fill and enter during dump; a clogged vent causes pressure damage or slow, erratic unloading.

Apparatus plumbing includes tank-to-pump, tank fill, dump valve, drain, and vent lines; labeling and valve position indicators speed operations under stress.

Weight distribution and axle ratings govern legal capacity; the tank, water, pump, and hose load must be balanced within GVWR and GAWR.

Fill site selection criteria: adequate sustained flow, safe apparatus access and egress, room to stage multiple tenders, and a water source that can be drafted or pressurized reliably.

Fill rate is limited by the smallest component: source capacity, pump capacity, hose size and length, and the tanker's vent and intake size.

Use large-diameter hard suction or LDH supply lines to minimize friction loss; a short 4-inch or 6-inch line delivers far more than several small lines.

Establish one-way traffic flow, a designated fill position, and a fill officer who controls when each tender moves; never let a driver self-dispatch from the queue.

Jet fill or a large direct fill line cuts cycle time; monitor the tank vent and stop filling when water appears at the overflow to avoid overfilling and spillage.

Record fill start and completion times and gallons loaded; cycle time data drives the shuttle calculation and reveals bottlenecks.

Drafting at a fill site requires a suitable hard suction, a strainer kept off the bottom, and a primer in working order; a low-water condition can break the draft.

Spill control and containment at the fill point protect the water source and comply with environmental requirements.

Dump site selection: firm, level ground that supports the loaded apparatus, a basin or portable tank large enough to receive the dump, and a clear, safe exit path for the empty tender.

Portable tank setup requires level ground, a liner or ground cover if specified, and the tank positioned so the tender's dump chute discharges into it without the apparatus overhanging the tank.

Dump rate depends on dump valve size and opening, chute condition, tank venting, and receiving tank capacity; a partially opened valve can extend the dump unnecessarily.

Dump valves should be opened gradually to control surge and splash, then fully to complete unloading; close before moving to prevent spill and valve damage.

A dump site must have a receiving pump or a dedicated engine with a large suction line to move water from the portable tank to the fireground; without it the tank becomes the bottleneck.

Keep the dump chute clear of the tank floor and liner, and never let the apparatus roll while the valve is open.

Dump site capacity is the sum of usable tank volume plus the rate at which water is drawn out; size the site to at least one full tender load of buffer.

Multiple tenders at one dump site require spacing, a traffic pattern, and a dump site officer to prevent collisions and cross-flow between tanks.

Shuttle flow formula: rate (gpm) = total water moved (gallons) divided by total cycle time (minutes); cycle time includes fill, travel loaded, dump, and travel empty.

Number of tenders needed = required fire flow / (tender usable capacity / cycle time), rounded up, plus a spare to cover breakdowns and refueling.

Reduce cycle time by shortening travel distance, increasing fill and dump rates, and improving traffic control; every minute saved adds flow.

Usable tank capacity is less than nominal capacity because of residual water and safe operating limits; use the actual delivered volume in calculations.

Large-volume movement needs a water supply officer, radio discipline, and a written assignment for each tender: fill site, route, dump site, and reporting point.

Dump sites should be sited near the fireground but off the primary access route, with enough area for staging, portable tanks, and a receiving pump.

Track each tender's arrival and departure times to compute actual cycle time and adjust the number of units; a stalled queue signals a bottleneck.

Mutual aid and tanker task forces should be requested early; building a shuttle from scratch costs more time than the fire flow calculation allows.

Relay pumping: each engine in series boosts pressure to the next; the required pressure at each pump is the downstream requirement plus friction loss in the connecting line.

Use the largest available hose for relay lines; 4-inch or 5-inch LDH carries far more flow at lower friction loss than multiple 2.5-inch lines.

Dual pumping uses two engines drafting from the same source and discharging into a common manifold or large line; balance the pumps to avoid one cavitating or overpressurizing the other.

Relay intake pressure should be kept positive; a relay engine should not be allowed to run dry or cavitate when the upstream pump falters.

Set relief valves and pressure governors to protect against water hammer when a pump in the relay changes speed or shuts down.

Communication between relay pump operators is essential; use radio or hand signals to coordinate throttle changes and confirm stable pressures.

Total friction loss in a long relay is the sum of losses in each hose section plus appliance losses; calculate before committing to a relay layout.

A relay can be extended with a nurse or manifold engine at the fireground to supply multiple attack lines from one large intake.

Establish command and assign a water supply officer early; the officer manages fill and dump sites, tender assignments, and the shuttle flow rate.

Use clear, standardized radio terminology and a dedicated tactical channel for water supply operations to keep the fireground channel free.

Accountability: every tender crew reports to a supervisor, and personnel must be tracked at fill and dump sites, not only at the fire building.

Traffic safety at fill and dump sites requires reflective vests, warning devices, lighting at night, and a traffic control plan for public roads.

Apparatus placement must allow rapid egress; never block the only exit from a fill or dump site, and keep a clear path for incoming tenders.

Driver fatigue and long shifts degrade judgment; rotate drivers and enforce rest periods during extended shuttle operations.

Emergency response and apparatus movement follow department policy and state law; due regard for safety always overrides speed.

After-action review should capture cycle times, flow achieved, and bottlenecks, and feed corrections back into the preplan and training program.