Hand-considered hypotheses, 5301–5400
Written one at a time, not composed. The subject is fire as a physical and chemical system: piloted and spontaneous ignition, flame spread, smoldering, soot and smoke optics, compartment dynamics, the mechanisms by which agents interrupt combustion, and the physics of detection. Each entry carries its own logical-form label and no label appears twice, so the variety is structural rather than topical; the entries argue about mechanisms and about tests that would separate them. None has been tested. No data are cited or reported, and every magnitude named below is an estimate, offered to fix an order of magnitude and not as a measurement.
Ignition and piloting
Apparatus-defined constant
H5301. Piloted ignition delay is usually reduced to a critical surface temperature, and that temperature is then quoted as a material property. The pilot, however, establishes a flammable layer at a standoff distance that depends on its own size and energy, so the temperature the surface must reach belongs partly to the igniter; a spark and a hot wire of equal energy should give two different critical temperatures for the same sample.
Regime misassignment
H5302. In a translucent fuel the radiant flux is absorbed over a depth, while the thermal wave penetrates a depth that shrinks as the flux rises. The apparent switch from thin to thick behaviour in ignition data may therefore be the switch from in-depth to surface absorption, which would place the transition at a flux rather than at a thickness and make the fitted thermal inertia an artefact of the fit. If that holds, an inertia fitted from one flux should disagree with the value from a step change on the same sample.
Non-monotone humidity response
H5303. Moisture is normally treated as an inert that delays ignition by absorbing heat. Water vapour also absorbs in the infrared and can warm the surface at a fixed external flux, while the same vapour dilutes fuel at the surface; because the two effects have opposite signs, ignition delay should pass through an interior maximum as humidity rises rather than climbing monotonically.
Orientation-hidden criterion
H5304. Critical surface temperature and critical heat flux are interchangeable only when the convective loss coefficient is held fixed. In still air that coefficient depends on the sample's orientation and size, so a horizontal upward-facing slab and a vertical one of identical material should give different critical temperatures, and the gap should track the calculated natural-convection coefficient rather than any chemistry.
Local-versus-mean control
H5305. A fuel carrying a distributed inert is characterized by its mean composition, yet ignition begins at the hottest particle-scale site. The critical flux for such a mixture should depend on the width of its particle-size distribution at fixed mean size, so two samples with identical averages but different widths should differ by more than run-to-run scatter.
Front-versus-bulk kinetics
H5306. The first mass-loss step in a cellulosic fuel is endothermic and confined to a thin layer at the heated surface. Its duration should therefore scale with sample thickness rather than mass, which means a kinetic rate extracted from a thick sample is a front velocity in disguise and will not transfer to a thin one.
Grouping breakdown
H5307. Ignition data for charring fuels are collapsed against the thermal-inertia group on the assumption that one group fixes the surface temperature history. Once a char layer forms, the relevant inertia is the char's rather than the virgin fuel's, so two materials matched in the group should diverge after a crossover time computable from the char depth.
Coincidental cancellation
H5308. At reduced pressure the gas-phase kinetics scale with the oxygen partial pressure while the convective losses scale with the total pressure. These dependences can cancel along one particular pressure path, and a pressure-independent ignition delay observed along that path would be evidence of cancellation rather than of a pressure-independent mechanism.
Pilot-composition effect
H5309. The pilot is modelled as a heat source of a given size and temperature. If its composition matters, a hydrocarbon pilot and a hot wire matched in temperature and size should produce different ignition limits, because the pilot delivers radicals the wire cannot, and the difference would be a direct measure of the radical requirement at ignition. The comparison also decides whether the pilot's contribution is catalytic, since a source that survives many attempts without depletion is not being consumed.
Loss-term dominance
H5310. At high flux the surface re-radiates a growing share of what it absorbs, so the net flux approaches a ceiling no increase of the source can lift. A thin low-emissivity coating that leaves the thermal inertia nearly unchanged should then raise the critical flux by close to the ratio of the emissivities, separating the loss term from the absorption term. Coated and uncoated samples of one substrate should then differ in critical flux by that emissivity ratio alone.
Permeability-controlled ignition
H5311. In a porous fuel bed the gas-phase reaction zone is fed by vapour that must flow out through the bed. Ignition delay should then be governed by the bed's permeability rather than by its thermal properties, and a bed compressed to half the permeability should ignite later even though its conduction and capacity are unchanged.
First-run bias
H5312. A freshly prepared surface carries adsorbed water and a labile fraction that are driven off on first heating. The ignition temperature measured on the first run should therefore be higher than on later runs, which makes that first number a statement about the sample's storage history rather than about the material.
Cup-geometry collapse
H5313. In an open cup the flammable vapour is continuously removed, while in a closed cup it accumulates, so the two devices sample different vapour pressures at the same liquid temperature. The ratio between the reported values should be fixed by the mouth-to-liquid distance and the ambient draft, which would make the difference a transport calculation rather than a property of the liquid. One cup design becomes convertible into the other by calculation rather than by a fresh calibration.
Electrode-loss artefact
H5314. Minimum spark ignition energy is read as a chemical quantity, but the kernel loses heat to the electrodes during its first instants of growth. The measured minimum should then scale with the electrode's thermal conductivity at fixed gap, and swapping electrodes without changing the mixture should move the minimum in a predictable direction.
Heating-rate criterion shift
H5315. A slowly heated solid gives its pyrolysis products more time to accumulate in the boundary layer before they are swept away. The surface temperature at ignition should therefore fall as the heating rate falls, which makes the critical temperature extracted from a slow ramp partly a residence-time criterion that will not predict ignition under a fast flux.
Flame spread and burning rate
Quench-distance control
H5316. Opposed-flow spread over a thick fuel is treated as a heat-transfer problem with a pyrolysis threshold. Near extinction the flame sits at the standoff distance where its heat loss to the surface outruns its reaction rate, so the spread rate close to the limit should correlate with the surface temperature at quenching rather than with the pyrolysis temperature.
Preheat-length dilution
H5317. In concurrent spread the flame preheats the fuel over a length set by its own boundary layer. Part of that heat is conducted ahead of the front and lost into the bulk, so a fuel of higher thermal conductivity should spread more slowly at equal volatility, with the penalty scaling as the ratio of conductivities. A conductivity series at fixed chemistry would test this without moving the pyrolysis temperature at all.
Interior optimum in thickness
H5318. Thinning a fuel sheet raises the spread rate because less heat is wasted in depth. Below a thickness comparable to the flame's standoff the flame can no longer be sustained against the substrate, so the rate must turn over and fall, giving a maximum at a thickness that belongs to the flame rather than to the fuel. The maximum is measurable by a thickness series under one ignition protocol, and it should move when the ambient oxygen changes.
Attachment-limited maximum
H5319. Upward spread accelerates with inclination while buoyancy keeps the flame attached to the surface. Beyond an angle at which the flame lifts off the rate should fall again, so the dependence on angle carries a maximum whose position moves with sample width, because width sets the buoyant inflow.
Two-mechanism separation
H5320. Char acts both as an insulating layer and as a barrier to fuel escape, and these roles develop on different time scales. A charring fuel's spread rate should be set by the char depth accumulated during the flame's residence time, so two fuels with equal char yield but different char permeability must spread at different rates.
Confinement enhancement
H5321. A flame spreading along a narrow channel entrains less than one on an open surface, so its preheat zone is longer and its spread faster. The enhancement should peak at a gap of a few flame thicknesses, an estimate rather than a measured optimum, and decay on both sides, which would make channel width a control variable as strong as the fuel's orientation.
Conductance-ratio control
H5322. On an insulated wire the metal core conducts heat away from the flame while the insulation confines the pyrolysis gases. The spread rate should be governed by the ratio of the core's axial conductance to the insulation's, so an insulated wire can outrun a bare one of the same metal because confinement outweighs the loss.
Lateral-loss width limit
H5323. A spreading flame loses heat sideways to the sample's edges as well as downward into the fuel. Below a critical width the lateral loss should exceed the flame's heat production and opposed spread should stop entirely, which would make width a hidden variable in every narrow-sample measurement. A width series at fixed thickness should show spread failing abruptly rather than fading gradually.
Finite-length bias
H5324. Spread rate is taken as distance travelled divided by time, on samples short enough to be convenient. The flame needs a development length before its preheat zone is established, so reported rates for one material should rise with sample length and approach the true rate only above a threshold that scales with the flame's standoff.
Radiation-limit crossover
H5325. Where buoyancy is absent, opposed spread is limited by radiative loss from the flame rather than by conductive gain to the fuel. The crossover between the two limits should sit at a fuel thickness where loss and gain balance, which makes thickness, not gravity, the parameter deciding whether a microgravity spread test is representative. Varying thickness at fixed pressure in a drop tower would locate the crossover directly.
Melt-transport amplification
H5326. A thermoplastic ahead of the flame forms a melt pool that can flow toward the flame and preheat fresh fuel by convection. The spread rate should then depend on the melt's viscosity, and a fuel that melts without flowing should spread at the rate of a thermoset with the same pyrolysis temperature. A viscosity series at fixed chemistry would predict spread rates that a pyrolysis-temperature model cannot reproduce.
Asymmetric obstruction
H5327. A hole in a thin fuel sheet feeds air into the flame on its downstream side and starves it upstream. The average spread rate past the hole should depend on the hole's diameter relative to the flame's standoff, so small holes should accelerate spread while large ones arrest it.
Gap regime between modes
H5328. Across a porous bed the smolder front needs oxygen through the pore space while a flame needs fuel vapour from it. There should be a void fraction at which neither propagates, because the bed is too open to sustain a front and too closed to release enough vapour for a flame, and both modes should fail at that one packing. A packing series at constant fuel and constant oxygen should show the two failures as one continuous gap.
Chamber-flow aliasing
H5329. Spread experiments run in still chambers whose residual buoyant circulation is never zero. The scatter between repeats should then be a function of the chamber's aspect ratio rather than of the material, and two laboratories with different chamber heights should report systematically different rates for the same sample. Rotating the chamber's aspect ratio about a fixed sample should change the measured rate, which is a cheap check on any material difference.
Marangoni coupling
H5330. Spread over a liquid is fed by the hot layer that the flame pushes ahead of itself. That flow is driven partly by the surface-tension gradient, so a surfactant that changes the gradient should change the spread rate while leaving the flash point unchanged, which separates the surface flow from the vapour supply.
Superposed fronts
H5331. A thick fuel can carry a fast surface flame and a slow in-depth front at the same time. A reported spread rate is then a weighted mean of the two, and its value should shift with the sensitivity of the instrument used, which makes cross-study comparison of the spread rate meaningless for thick fuels. Separating the two fronts needs a depth-resolved measurement, which a surface camera cannot supply.
Pre-exposure memory
H5332. A sample heated without igniting retains a char layer whose absorptivity exceeds the virgin fuel's. Spread over such a sample should be faster than over virgin material by an amount set by the char's optical depth, so virgin and aged specimens of one fuel are not the same experiment.
Momentum-versus-buoyancy regime
H5333. Under a ceiling the flame is fed by a horizontal jet whose momentum, not the plume's buoyancy, sets the inflow. Spread should then scale with a Froude number built on the jet velocity rather than with the fuel's orientation, and the same fuel should spread faster on a ceiling than on a vertical wall at equal incident flux. Repeating the ceiling test at two ceiling heights would separate the jet's momentum from the plume's buoyancy.
Smoldering and porous fuels
Upstream-diffusion control
H5334. The oxygen that feeds a smolder front must reach it through the residue the front has already left behind. The front's speed should therefore be governed by the permeability of that residue, and a fuel leaving a dense ash should smolder more slowly than one leaving a friable ash even when the two fuels are chemically similar.
Lagging maximum
H5335. Char oxidation continues behind the smolder front, where oxygen is still available and the temperature is still high. The peak temperature should therefore lie behind the visible front, and a thermocouple placed at the front should under-report that peak by an amount that grows with the front's speed.
Two-mechanism threshold
H5336. Moisture slows smoldering by absorbing heat and by displacing oxygen with steam in the pore space. The second effect should dominate above a moisture content lower than the commonly assumed one, and a moisture series run in oxygen-enriched air should separate them because enrichment restores the oxygen the steam displaced. One moisture series run twice, in air and in enriched air, gives both thresholds from a single apparatus.
Local-nucleation statistics
H5337. The transition from smoldering to flaming begins at a localized hot spot that must exceed a critical size before it can grow. The transition should therefore be stochastic in time but with a per-volume rate that is a material constant, so a bed of twice the volume should show the transition after roughly half the wait. Both ratios are estimates rather than measured values, and the per-volume rate is the quantity that should transfer between beds.
Competing ash roles
H5338. Ash insulates because its conductivity is low and catalyzes char oxidation because its alkali content is high. Those two roles push the smolder rate in opposite directions, so ashes from different fuels should change the rate with a sign that follows the alkali-to-silica ratio rather than the ash content alone.
Configuration collapse
H5339. Forward and reverse smolder differ only in the direction of the oxidizer's convective supply relative to the front. Once the Darcy velocity exceeds the diffusive flux the two configurations should separate, and below it they should coincide, so a difference reported at low flow is more likely to be buoyancy in the apparatus.
Self-limiting depth
H5340. A smolder front consumes oxygen at a rate that rises with the char's reactivity and is replenished at a rate that falls with depth. The front should extinguish at a depth set by the bed's permeability, which would give a maximum penetration independent of how much fuel remains beneath it. A bed loaded well above that depth should still stop in the same place.
Lateral-loss depth criterion
H5341. A dust layer loses heat sideways to its container as well as downward into the substrate. The minimum depth for propagation should therefore be set by the ratio of lateral loss to reaction heat, so a more volatile dust can propagate in a thinner layer despite igniting at a higher temperature.
Ratio as structural probe
H5342. The carbon monoxide to carbon dioxide ratio in smolder effluent is commonly read as a temperature indicator. It is more likely set by the residence time of the gases in the char, so the ratio should track the bed's pore structure and change when the bed is repacked at constant temperature.
Flow-rate optimum
H5343. Forcing air through a smolder bed raises the oxygen supply and the convective cooling together. The front speed should therefore peak at a Darcy velocity where the two are comparable, and beyond it the front should slow and then extinguish rather than accelerate without limit. The peak is located by a flow series at constant bed depth, because depth and flow both change the supply.
Residue property change
H5344. The black residue behind a smolder front is treated as inert char. It is partly oxidized material of higher surface area and lower ignition temperature than the virgin fuel, so a re-ignition test on the residue measures a different substance and cannot return the original fuel's threshold.
Apparent activation energy
H5345. Above a threshold the smolder front's speed is limited by how fast heat diffuses into unburned fuel rather than by the reaction rate. The activation energy inferred from speed against temperature is then the temperature dependence of the thermal diffusivity, which is small and would show up as an implausibly low value. A speed-against-temperature series on a bed of fixed permeability would show that weak dependence as a low apparent activation energy.
Soot, smoke optics, and radiation
Path-dependent yield
H5346. Soot yield is tabulated per fuel as though it were a constant. Soot formed early in a flame can be oxidized later in the same flame, so the yield depends on the temperature history the particles see, and two burners with the same fuel and different residence times should give different yields.
Optical-thickness bound
H5347. The fraction of a flame's heat released as radiation is taken as a fixed value for a given fuel. That fraction is bounded by the flame's optical thickness, so it should rise with flame size while the flame is optically thin and saturate once it is thick, and any tabulated constant is then a coincidence of the sizes that were measured. Two pan diameters would test the claim without any knowledge of the soot yield.
Calibration-morphology bias
H5348. Smoke mass concentration is inferred from light extinction with a mass-specific coefficient calibrated on one soot morphology. Freshly formed soot is more branched and carries a different coefficient, so the inferred mass should be biased high for young smoke and converge on the calibration value as the smoke ages.
Instrument-scattering leakage
H5349. Soot is treated as purely absorbing in the near infrared because its single-scattering albedo is reported close to zero. Part of that zero may be scattered light the receiver's aperture fails to collect, and closing the aperture should reveal a finite albedo and correspondingly lower emissivity than radiation models assume.
Sub-thermal chemical marker
H5350. Alkali metals suppress flames at doses that also depress temperature. At lower doses they quench soot luminosity without measurably cooling the flame, so a change in visible emission should precede any thermocouple response and can serve as a chemical marker of inhibition at sub-thermal dose.
Oxidizer-identity error
H5351. Soot oxidation in the post-flame zone is usually attributed to molecular oxygen. It is more likely limited by the hydroxyl radical's availability, so an additive that scavenges hydroxyl should reduce soot burnout and raise the smoke yield even while it lowers the flame temperature only slightly. Adding a radical probe downstream would shift the smoke yield in the direction the hypothesis requires.
Agglomeration inversion
H5352. Smaller primary soot particles collide more often, so a smoke with a finer primary size should agglomerate faster. Its optical equivalent diameter after a fixed residence should therefore be larger and its extinction per unit mass lower, which is the opposite of what a size-based argument predicts.
Universal kernel claim
H5353. Brownian coagulation of smoke particles in the free-molecular and transition regimes has a rate coefficient that does not depend on the fuel. The decay of particle number with time should then be a universal function with the fuel setting only the initial number, so one curve should fit smokes from unrelated fuels.
Grey-gas bias
H5354. Radiation models treat the smoke layer as grey. Real smoke has a window in the near infrared where the fuel's own flame radiates strongly, so a grey model should overestimate flux from a thin layer and underestimate it from a thick one, with the sign changing at an optical depth of order one, itself an estimate and not a measured crossing. A two-band radiometer would show the window directly, and its reading should diverge from a grey model as the layer thickens.
Near-field view-factor reversal
H5355. Flame-to-target flux is often computed with a point-source view factor. Closer than a few flame widths the flame's finite extent matters, and the error should change sign at a distance set by the flame's aspect ratio, so a point-source model is conservative at one separation and unconservative at another.
Projected-depth effect
H5356. Tilting a flame is treated as redistributing the same radiation over a different geometry. The tilt also changes the optical depth along the line of sight, so a tilted flame should radiate more toward a target on the side it leans toward even at unchanged volume and temperature.
Particle-thermal lag
H5357. Laser-induced incandescence infers soot volume fraction from particle emission, assuming the particles track the local gas temperature. The particles carry their own thermal inertia, so in a flickering flame the inferred field is a smoothed version of the true one and its apparent peak sits below the real peak. The lag grows with the square of particle diameter, so a field with a wide size spread is smoothed unevenly.
Surface-quench origin
H5358. Carbon monoxide in a well-ventilated fire is attributed to flame chemistry. Much of it may be produced where the flame quenches against the fuel surface, so the yield should correlate with the fuel's surface area and char content rather than with its gas-phase stoichiometry. A fuel of high surface area and low char yield should then make more carbon monoxide than its flame chemistry alone implies.
Aperture-dependent coefficient
H5359. Transmissometers report a mass-specific extinction coefficient as a property of the smoke. Forward-scattered light enters a wide-aperture receiver, so the coefficient measured with a wide aperture should be lower than with a narrow one by an amount computable from the soot's size parameter, which makes the coefficient partly a property of the instrument.
Sampling-location mismatch
H5360. Smoke in a ceiling jet is sampled to characterize the upper layer. The jet's shear strips agglomerates, so its size distribution should be finer than the layer's, and optical properties inferred from jet samples should not transfer to the layer without a size correction.
Radiative extinction size
H5361. A flame loses a larger fraction of its heat to radiation as it shrinks, because its surface-to-volume ratio rises. There should therefore be a minimum size for sustained burning set by the radiative loss fraction, and below it a flame should extinguish even with fuel and oxygen in plenty. Shrinking a pan until the flame lifts, at constant fuel and ventilation, would bound the minimum size.
Spectral suppression signature
H5362. Chemical inhibition reduces a flame's soot loading more than its temperature at low dose. The ratio of emission in two spectral bands should therefore shift characteristically when an inhibitor is present, which would let a radiometer distinguish chemical from physical suppression without drawing a gas sample.
Compartment dynamics and ventilation
Potential-core violation
H5363. Ceiling-jet temperature correlations assume a point source at the fire. Within a few source diameters the jet still holds a potential core, so the correlations should overpredict decay near the fire and underpredict the temperature there, with the discrepancy vanishing beyond a distance that scales with the fire's diameter.
Saturation of a coefficient
H5364. Plume entrainment is assigned a constant coefficient. Entrainment should rise with the plume's Richardson number while the flow is laminar and saturate once it is fully turbulent, so the accepted constant is a saturated value and small-scale plumes should entrain proportionally less. A plume series spanning a decade in heat release should show the coefficient approaching its saturated value from below.
Leakage-ratio control
H5365. The neutral plane in a compartment fire is located from the vent's height. It should instead be set by the ratio of upper to lower leakage areas, so a compartment with a large high leak and a small low leak should place its neutral plane above the vent's midpoint at the same fire size. Two compartments with equal vents and different leak distributions should place the neutral plane at different heights.
Model-validity boundary
H5366. The two-layer description assumes the plume delivers smoke to a sharp interface. When the plume's momentum at the interface exceeds the buoyant spreading there, the interface should thicken with time rather than descend, and the breakdown should occur at a Froude number of order one, an estimate to be located rather than a fitted value.
Damkohler precondition
H5367. Backdraft is described as a condition of the fuel. It should instead require the inflow's Damkohler number to exceed a threshold when the opening is made, so one compartment can backdraft or merely burn depending on the opening's size relative to the fire's heat release, and the precursor plume is fuel-rich gas mixing below its ignition temperature.
Criterion non-equivalence
H5368. The three common flashover criteria, upper-layer temperature, floor heat flux, and flame from the opening, are treated as indicators of one event. They are thresholds on different variables and should disagree systematically, most strongly in small compartments where the layer is thin and the floor flux is dominated by the flame's direct radiation. Their disagreement should be reproducible, and its size should order the criteria rather than the compartments.
Mixing-versus-supply
H5369. Burning rate in an under-ventilated compartment is tied to the air supply through the opening. It should be limited instead by the mixing of fuel-rich gases with incoming air near the opening, so the rate should scale with the opening's area and inflow velocity but with an exponent differing from the ventilation-limited correlation.
Adjacent-plane distinction
H5370. Two heights in a compartment, the neutral plane and the flow reversal, coincide only when the fire is centred. A fire near a wall biases the inflow through the wall's boundary layer, so the two heights should separate by a fraction of the opening height, and that separation has probably been read as noise.
Inverse-problem claim
H5371. In a sealed compartment the pressure rise during a fire is resisted by leakage flow, which is quadratic in the pressure difference. The shape of the pressure history should therefore reveal the effective leakage area independently of the fire's growth rate, turning the pressure record into a measurement of the enclosure rather than of the fire. A compartment tested at two known leak areas fixes the calibration of that inverse problem before it is applied to an unknown one.
Steady-state selection
H5372. A fire travelling along a long corridor should settle at a speed set by the ratio of heat release per unit length to heat loss per unit length, without reference to spread kinetics. The transient before that speed is reached is where spread physics still matters, so corridor tests short enough to remain in the transient measure a different quantity.
Age as a hidden clock
H5373. Smoke in the upper layer is older than the ceiling jet that delivered it by the turnover time. Its carbon monoxide to carbon dioxide ratio should therefore keep evolving after the smoke leaves the flame, which makes the ratio a clock for residence time as much as an indicator of combustion conditions.
Missing geometric variable
H5374. Switching between fuel-controlled and ventilation-controlled burning is indexed on the ventilation factor alone. The plume's residence time also depends on the compartment's height, so two compartments with equal ventilation factors but different heights should fall on different sides of the transition. Fixing the ventilation factor while changing only the height is a test no existing correlation would pass.
Perimeter scaling
H5375. Pool burning rate is expressed per unit surface area. The flame's edge is better ventilated than its centre, so the rate per unit area should rise with the pool's perimeter-to-area ratio, and a long thin pool should burn faster per unit area than a square one of equal area. A pan of fixed area cut into strips should show the effect with neither fuel nor ventilation changed.
Shape-dependent collapse
H5376. The ventilation factor combines an opening's area and height into one number. Openings of equal factor but different aspect ratios place the neutral plane differently, so a wide low opening and a tall narrow one should give different burning rates and the factor should be seen as hiding a shape dependence.
Dominance crossover
H5377. Floor heat flux during the growth phase is modelled as radiative from the upper layer. Convective impingement from the ceiling jet should dominate early, with the crossover to radiative dominance at the layer temperature where the fourth-power term overtakes the jet's mass flux, so early-growth flux data should not extrapolate to flashover conditions. A floor gauge with and without a convective shield would separate the two terms without a model.
Self-accelerating descent
H5378. Smoke layer descent is modelled as a filling process at constant volume production. As the layer heats, the plume's buoyancy and volume flux grow, so the descent should accelerate in a way that depends on the layer's temperature as well as the fire's mass loss, and the interface should curve in time in a manner filling models do not produce.
Entrainment-interaction claim
H5379. A fire in a corner draws air along two walls, and the two entrainment patterns interact. The result should be a vertical velocity maximum above the fire and a ceiling jet faster than a free plume's at the same heat release, so the corner's apparent enhancement is an entrainment effect rather than an enhanced heat transfer.
Residual-oxidation floor
H5380. Oxygen depletion is assumed to extinguish a compartment fire. Char can oxidize at oxygen concentrations below those that support a flame, so there should be a residual oxygen floor below which the flame dies but the fuel does not, and a compartment that appears burned out should still hold a heat source. The floor's oxygen concentration should then decay to a non-zero plateau that a flame-only model cannot produce.
Agents and suppression mechanisms
Stokes-number optimum
H5381. The optimal droplet size for a water mist is usually chosen from heat-transfer arguments. Droplets below a critical Stokes number follow the gas into the reaction zone while larger ones cross it ballistically, so the optimum should shift with the fire's strain rate, and a mist tuned to a small fire should underperform on a large one. One nozzle tested at two fire sizes should show the predicted loss of performance.
Mechanism misassignment
H5382. Water mist is credited mainly with absorbing heat through vaporization. For fine mists the dominant effect in the reaction zone may be the displacement of oxygen by the steam produced, so effectiveness should scale with the vapour volume generated per unit mass of liquid rather than with the latent heat, and a liquid of higher latent heat but lower vapour yield should do worse.
Stoichiometric ceiling
H5383. A radical scavenger terminates chains in proportion to the radicals it can consume. Beyond the dose matching the flame's radical production, additional agent can only dilute and cool, so the effectiveness curve should carry a knee at that dose and the ranking of two agents should depend on which side of the knee they are compared. Two agents of equal radical affinity but different volatility should show the knee at the same dose, which separates stoichiometry from transport.
Competing dilution and cooling
H5384. Inert gas extinguishing concentrations are ranked by heat capacity. A denser gas also displaces more oxygen at the same volume fraction, and the two effects oppose, so the extinguishing concentration should pass through a minimum at an intermediate heat capacity rather than fall monotonically.
Heat-up-time optimum
H5385. Dry chemical powders are assumed to work better the finer they are. A particle must heat to decomposition before it can inhibit, and a very fine particle follows the flow so closely that it leaves the reaction zone before heating, so effectiveness per unit mass should peak at an intermediate size set by the ratio of heat-up time to residence time.
Evaporation-limited lifetime
H5386. An aqueous foam's endurance on a fuel surface is attributed to its drainage time. The film's life should instead be limited by evaporation at the hot fuel surface, so a foam with fast drainage but high water content should outlast a more stable one, and endurance should scale with the fuel's surface temperature rather than with foam stability. A drainage series and an evaporation series on one foam would separate the two lifetimes.
Marginal-dose intensification
H5387. Cooling a charring fuel is assumed to lower its pyrolysis rate monotonically. A small water dose deposits its latent heat at the surface, and the resulting steam can crack the char and expose fresh fuel, so an application rate below a threshold should raise the burning rate before it lowers it.
Mixing-time bound
H5388. The time to extinguish a compartment fire is bounded below by the time needed to mix the agent with the upper layer. A less effective agent that mixes faster can therefore extinguish sooner than a more effective one, and agent rankings from enclosure tests should depend on the discharge's momentum as much as on the agent's chemistry.
Surface-recombination scaling
H5389. Condensed aerosols are thought to inhibit through gas-phase chemistry. Their particles also provide surfaces for radical recombination, so effectiveness should scale with specific surface area and should fall sharply when the particles agglomerate in the hot layer before reaching the flame, which makes transport as important as composition.
Phase-specific extinction
H5390. A fire that stops flaming is called extinguished. A suppressed fire can retain a char core above the char oxidation threshold, so extinction is a statement about the gas phase only, and the core's cooling time should be set by the char's thickness rather than by the agent's dose.
Penetration scaling
H5391. A spray's penetration into a buoyant plume depends on the droplets' Stokes number and the plume's velocity. The droplet size needed to penetrate should grow with the fire's size faster than linearly, because a larger fire both accelerates the upflow and thickens the reaction zone, so one nozzle specification cannot cover a range of fire sizes. The penetration threshold should appear as a sharp change in the fraction of droplets reaching the flame, not as a gradual loss.
Temperature-window claim
H5392. Activation and decomposition bracket the temperatures over which a radical scavenger can work at all. Its effectiveness should therefore be confined to a temperature window, so an inhibitor chosen for a premixed flame's temperature should underperform on the cooler, fuel-rich side of a diffusion flame.
Dual-description identity
H5393. Suppression by inerting and suppression by fuel removal are described as different mechanisms. They are one reduction of the fuel-to-oxidizer ratio at the reaction zone, seen from the oxidizer side and from the fuel side, so the effectiveness of a surface blanket should depend on the fuel's surface temperature rather than on oxygen displacement. A blanket applied at two fuel temperatures should give two effectiveness curves for the same agent.
Area-scaled re-ignition
H5394. The chance that a suppressed fire re-ignites is tied to how much fuel remains. It should scale with the exposed hot surface area instead, so a thin spread-out residue should re-ignite more readily than a compact one of the same mass, and tests on consolidated samples should not predict the behaviour of distributed ones.
Detection physics
Path-integral misreading
H5395. Obscuration measured across a compartment is a line integral through a stratified layer. A beam at the layer's midpoint reads a value between the layer's concentration and the lower zone's, so reported obscuration should change with beam height at constant smoke production, and a single beam cannot define a concentration. The vertical profile of obscuration, rather than one reading, is therefore the quantity comparable between compartments.
Transport-dispersion bias
H5396. Aspirated detection transports smoke through a pipe before analysis. The pipe disperses the sample in time, so a step in concentration arrives broadened, and two installations with identical detectors but different pipe lengths should show different effective sensitivities, with the difference growing as the square of the transport time.
Sensor-target divergence
H5397. Ultraviolet flame detectors respond to emission from excited nitric oxide and hydroxyl in the flame. The agents that suppress a flame quench those emitters at doses below those that stop combustion, so a detector can report no flame while a smolder persists, and the divergence should be reproducible as a function of dose.
Rating-versus-application mismatch
H5398. A fixed-temperature heat detector is rated by the temperature at which it operates. Its response is set by its thermal time constant as well as that rating, so the same unit presents different effective thresholds to fast and slow fires, and the rated value is a steady-state number a growing fire never reaches. A ramp at two heating rates therefore yields the time constant and the rating from one run.
Scene-dependent sensitivity
H5399. Video smoke detection infers smoke from changes in image contrast. The detectable change depends on the scene's spatial contrast at the scale of the smoke's texture, so one algorithm should show different sensitivity on a plain wall and a textured one at equal smoke density, making sensitivity a property of the installation.
Transport bound on detection
H5400. Every point detector waits for smoke to arrive. That wait is set by the plume's buoyancy and the ceiling height, so no improvement in the sensing element can push the total time below the transport time, and the transport term should separate from the sensing term when one detector is tested at two ceiling heights. Subtracting the two arrival times leaves the sensing lag, which is the only part the hardware can improve.
Status
100 entries, H5301–H5400. The forms are uneven in weight on purpose: some are bounds, some are identity or degeneracy claims, several assert that an accepted criterion measures the apparatus, and a few are worth writing only because a fire laboratory could falsify them with equipment already on the floor.
If one of these is worth an experiment, it is H5339 — that forward and reverse smolder coincide below the Darcy velocity at which convection overtakes diffusion, so any difference reported at low flow is buoyancy in the apparatus. It needs one bed, one flow controller and two thermocouple rakes.
Incoprea Research · hand-considered hypotheses 5301–5400 · 3 November 2026 · ~/Desktop/Nov3/