Testing a 9 MW Claim Against the Openings and the Fuel Package
A 4.2 m x 3.4 m second-floor bedroom with a 2.4 m ceiling has one door (0.9 m x 2.0 m) that stood open and one window (1.1 m x 1.0 m) whose glazing self-vented and was gone before suppression. Interior evidence: dense alligator char across the ceiling and the upper third of all four walls, heavy soot down to the floor line, a mattress burned down to the springs in the room's center, and a PVC clock-radio on a nightstand melted into a flat puddle. A gas water heater on the far side of the common wall shows an intact pilot assembly and no thermocouple deformation. The plaintiff's expert opines the fire reached 9 MW within six minutes and burned freely for fifteen minutes before the first line advanced. You must test that claim against the openings, the fuel package, and the interior evidence.
1. Using Q = 1500 x A x square root of H (kW), estimate the ventilation-limited heat release rate for (a) the door alone and (b) the door plus the failed window. Is 9 MW supportable, and what does this correlation not tell you?
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Door alone: A = 0.9 x 2.0 = 1.80 m-squared; square root of 2.0 = 1.414; A times root H = 2.55; Q = 1500 x 2.55 = about 3.8 MW.
Door plus window: window contributes A = 1.1 x 1.0 = 1.10 m-squared, root H = 1.0, so 1.10; total A times root H = 3.65; Q = about 5.5 MW.
Conclusion: 9 MW would require A times root H of about 6.0, roughly a 2.5 m-squared opening 2 m tall. Neither configuration supplies that. The claim is not supportable from the openings unless the expert produces an oxygen-consumption or mass-loss calculation.
Caveats that show judgment rather than recall: the correlation is an order-of-magnitude upper bound for ventilation-controlled, post-flashover burning of wood-crib-like fuels; it does not apply pre-flashover, and it ignores door sill height, smoke layer descent, and the fact that the window likely failed late, so the early period was door-only. The window being gone at the time of your inspection does not mean it was gone at minute six.
2. Independently of ventilation, can the fuel package in this room deliver 9 MW for fifteen minutes? Show the arithmetic and state the conclusion.
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Energy demand: 9 MW x 900 s = 8,100 MJ.
Fuel demand: at roughly 20 MJ/kg for typical cellulosic and foam fuels, that requires about 405 kg of combustible material; even at an optimistic 30 MJ/kg it requires about 270 kg. A bedroom containing one mattress, bedding, two nightstands, and a clock-radio is on the order of 60-120 kg of fuel. The room runs out of fuel long before it runs out of time.
Transient check: polyurethane foam at about 25-30 MJ/kg would have to be consumed at about 0.3 kg/s to make 9 MW. A 15-20 kg foam core therefore sustains that rate for well under two minutes, and single upholstered items in furniture-scale calorimetry commonly peak in the 1-3 MW range depending on construction and cover fabric.
Conclusion: the fuel-limited peak is the controlling constraint early in the fire, and the ventilation limit controls later. A 15-minute free burn at 9 MW is contradicted by both. The defensible statement is that the fire was fuel-limited during growth and ventilation-limited after flashover, with a peak in the low single-digit MW range.
3. What does the melted clock-radio puddle legitimately support, and what would you refuse to conclude from it? How do the soot and char patterns interact with the ventilation-limited finding?
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Legitimate inference: thermoplastics such as PVC and ABS soften and deform at roughly 100-150 degrees C and can pool when in sustained contact with flame or a hot surface, so the puddle supports that the nightstand area saw sustained heat. It is consistent with, and corroborative of, an origin or spread in that vicinity.
Refuse to conclude: that the puddle establishes a specific temperature, a duration, or a heat flux. Pooling depends on orientation, the item's mass and geometry, proximity to flame versus radiant flux, and whether molten polymer was consumed as fuel. Using it as a thermometer is a classic overreach.
Pattern interaction: heavy soot down to the floor, deep alligator char, and a fully consumed center fuel package are consistent with a hot, under-ventilated compartment. In a ventilation-limited fire, char depth and soot density record heat and duration of exposure, not heat release rate, so they cannot rescue the 9 MW claim. They also explain why the fire did not run out the open door: the openings were already the limiting factor. Document the radio, photograph it in place, and retain it only if its condition is disputed.