Tanker shuttle water supply at a woolshed fire
At 14:20 on a dry nor'wester, a scrub fire is running up a pine block toward a woolshed holding 400 round bales and two tractors. There are no hydrants within 6 km; water must be shuttled from a river fill point 4.2 km from the fire. You have two tankers on scene. Tanker 211 carries 9,000 L and has been completing the full fill-travel-dump-return cycle in 14 minutes. Tanker 214 carries 6,500 L and has been completing the cycle in 11 minutes. The incident controller has calculated that protecting the woolshed needs a sustained 1,800 L/min at the fireground for at least the next 25 minutes, and the structure sector already has one attack line and a deluge set running. A third tanker, 208, is 25 minutes away with an 11,000 L tank; it would need 8 minutes to fill before its first dump and would then cycle in 16 minutes. ComCen asks you for a water supply assessment now.
1. Can Tankers 211 and 214 sustain 1,800 L/min for the next 25 minutes? Show your working.
Read the worked answer
Convert each tanker's cycle into a sustained flow rate:
- Tanker 211: 9,000 L ÷ 14 min = 643 L/min
- Tanker 214: 6,500 L ÷ 11 min = 591 L/min
- Combined steady-state supply = 1,234 L/min
Requirement: 1,800 × 25 = 45,000 L over the window. Supply at 1,234 L/min over 25 min = 30,850 L. Shortfall = 14,150 L, or about 566 L/min (roughly 31% below requirement).
Two things make the real position worse than the arithmetic. First, 1,234 L/min is a best case: it assumes a full dump every trip and no queuing at the fill point or the dump point. Second, the opening minutes are the weakest, because neither tanker has dumped yet when the fire front reaches the woolshed, so the fireground is drawing on whatever is already in the dam or the appliance.
The honest answer to ComCen is that a two-tanker shuttle cannot hold 1,800 L/min, and the gap has to be closed before the front arrives, not after.
2. Does adding Tanker 208 close the gap? At what point does its water actually arrive?
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Steady state with three tankers:
- Tanker 208: 11,000 L ÷ 16 min = 688 L/min
- New total = 1,234 + 688 = 1,922 L/min against a 1,800 L/min requirement, a margin of about 7%.
So on paper it covers the demand, but only after its first dump. Timing: 25 min travel + 8 min fill + travel to the scene (say 5 min) is roughly 38 minutes before the first water arrives. The 25-minute critical window is already closed by then, so Tanker 208 does nothing for the period the incident controller is actually worried about.
The 7% margin is also thinner than it looks. One missed cycle by 211 costs 9,000 L, which is five minutes of the required flow. With three tankers plus support vehicles on a 4.2 km access road, queuing at the fill point will lengthen cycle times, and one delayed trip wipes out the margin. Report it as: covers steady demand only if nothing goes wrong, and arrives too late for the critical window.
3. What do you report to the incident controller, and what actions do you take in the next few minutes?
Read the worked answer
Report the numbers plainly and early: supply is about 1,234 L/min against a 1,800 L/min requirement, a shortfall of roughly 566 L/min, and the extra tanker will not arrive in time to change the next 25 minutes. Do not soften it, and do not wait for the shortfall to become visible as a falling tank level.
Actions, in order:
- Request through ComCen at least two additional tankers from neighbouring brigades, plus a portable dam or reservoir so tankers can dump without tying up the appliance.
- Look for on-site water now - stock tanks, a farm dam, a trough supply - and confirm access for a pump.
- Reduce demand to what the supply can actually support: run the deluge set only when bales are actually being wetted, and consider a defensive posture protecting the tractors and fuel rather than an internal attack the water cannot back up.
- Tell the structure sector commander the sustainable flow, so crews are not committed to a line that will run dry.
- Plan for the long haul: tanker fuel, driver relief, and a written record of the decisions and the times they were made.