The MH370 Bottom Line
Ques: How would an oxygen flare fire at cruising altitude differ from one on the ramp?
Response:
1. Two characteristics dominate once an oxygen fire starts up on the flight deck at cruising level. Firstly, upon ignition, the source is initially going to be a point-source and the fire's effect is concentrated, which is why its effect is referred to as a "blowtorch". Secondly, because it's not an actual blowtorch by design, that point-source will be always consuming its immediate surrounds at quite a rate - as well as weakening the close adjacent (to the side console) fuselage skin. We've seen that ultimate fuselage holing outcome in all of the oxygen fires on the ground - and that hull rupture effect airborne will be strengthened by the cabin pressurization's differential pressure. At cruise altitude, that fuselage hull is, in this context, like a fully blown-up balloon seeking its own envelope's weak-point.
Eventually that "blowtorch" will no longer be a point source per se. The net effect of that "spread source" would be that, quite soon, an even larger volume of oxygen (per second) will be entering the cockpit - and the environment in that enclosed area could best be described as increasingly oxygen-enriched. i.e. The oxygen from the flight-deck oxygen bottles will be flooding in at an increased rate. Think of it as being the difference between the initial delivery flow-rate of a water-hose with a constricting nozzle - and ultimately that of one without one (i.e. one with the nozzle wide open).
Consider the example of a seemingly very contrary, even contradictory, scenario. A cooking gas bottle's valve has been opened in a confined space with a lit stove close by. Until that gas in the enclosed environment becomes concentrated enough to support combustion, there will be no explosion. However, once it becomes a gas-enriched environment, that combustible gas will eventually and inevitably explode. Is that scenario any different from an oxygen flood in an enclosed environment? Yes, it's quite different - because oxygen isn't combustible, it merely supports combustion - and that's a BIG difference... in fact HUGE. Why so? It means that all the oxygen entering the enclosed space isn't being consumed - as would the cooking gas . That oxygen is (in direct contrast) constantly enriching the air in the enclosed space of the flight-deck. The rate of air swap-out attributable to the air-conditioning is minuscule by comparison. And only a very small percentage of that O2 is lost to the oxidation of combustion on the side console. In the ramp fires the flight-deck door would have been open, so the rate and level of oxygen-enrichment would have been much less (than in the cruising level circumstance). Think about that.... and think again about the extreme differences between the ground and cruising level scenarios.
Firemen fear the effect of introducing oxygen to an oxygen-starved fire, because an act as simple as opening a building's door can cause a searing killer flash-over. Introducing oxygen to the flight-deck gradually at first - then massively (via a cylinder-flood) will accomplish much the same effect as quickly opening a door and allowing mere air to flow in to an oxygen starved fire-front. Once you transition from oxygen-starved to an instantaneous 100% oxygen supplied O2 saturation level - in an inferno environment, there will be (eventually) a sudden incendiary flash-over. It's a stark fact of life, no guesstimation here on this..
2. Before dismissing these plausibilities, we should remind ourselves that we are expanding upon actual historical prior events (i.e. the ample precedents). Let's estimate that after around two minutes of that flight-deck oxygen fire, a number of thresholds would've been reached:
a. The flight-deck's fuselage skin would be quite weakened by the close-adjacent blowtorch - and bulging outwards due to the pressurization system's differential pressure (around +5 psi)
b. Pilot attempts to fight the fire with hand-held extinguishers would be having nil effect upon it i.e. a given truism, but one likely lost upon the pilots - they aren't trained for (nor could they conceivably recognize) this unique circumstance. One pilot would have had to quickly leave his seat. The urgency of landing ASAP would have led to a heading for the nearest suitable airfield being wound in..... and a 30 seconds rate-one bog-standard autopilot turn immediately commenced.
c. At around the two minute point (give or take 30 seconds) the intense heat of the blowtorch effect would have weakened the fuselage skin to the point where it could easily be holed by the overpressure of a flash-over.... as assisted by the pressurization differential.
d. Once that flash-over's over-pressure occurred, would its duration have been limited to around 5 seconds due to the weakened fuselage side quickly blowing out and the enriched oxygen atmosphere being instantly replaced by a "scooped up" oxygen-thin, environmentally frigid inflow. The pilots' lungs may have been seared in that 5 second interlude, but it wouldn't necessarily be a fatal consequence (i.e. depending whether or not they had their full-face masks on at that point). i.e. Would they have had their full-face masks on at that point? Quite likely they would have donned them as an SOP action because of the visible fire 90 seconds earlier. If so, the debilitating lung searing just would not have occurred and they'd have been in good shape to enter into the next phase of their baptism of fire. Which was?
e. First reflect upon the very short finite duration of an oxygen flash fire if its associated overpressure had ruptured the weakened hull - thus causing the abrupt loss of the oxygen enriched environment? Would this "flare kill-off" tend to have minimized pilot injuries, particularly if they were wearing their full-face masks? That's quite likely. In fact it's likely that one of the two pilots was seated, had limited exposure to the flare and entered an emergency descent as soon as the flare subsided. However without a flow of oxygen to his mask, the time of useful consciousness at that height (of around 30 seconds) would have intervened well before any stable trimmed descent profile was able to be established. Up to this point any surviving pilot would have been well behind the eight-ball as far as trouble-shooting their situation goes. However the distinctive aural depressurization alarm would have dictated a rote action of emergency descent entry in any trained pilot.
f. What else may have happened at that point of flash-over? It would have been at this point that comms sets and transponders were disabled by the heat's effect upon the plastic switches and the thermally trippable circuit-breakers on the flight deck. As to which ones and why them? It would depend upon which side the fire erupted, how much shielding there was of centre, ceiling and side consoles, instrument and CB panels (by the pilots' bodies etc).... and the individual characteristics and types of plastic switches impacted by the heat.
g. If you don't accept the eventual oxygen flare's overpressure as a cause of depressurization, note that many of the precedents (USN x3, A9-300, QANTAS 747, SCAT Airlines 737) have had the oxygen cylinders exit through the fuselage.
3. Conclusion The oxygen flash-fire's hypothetical overpressure holing of the fuselage could've both rapidly extinguished the flash-fire and cooked off the cockpit depressurization alert. It's a safe bet that neither pilot would've ever realized that the origin of the fire was their oxygen system, so they would have reacted instinctively to hearing that aural pressurization alarm by donning masks, disconnecting the autopilot and stuffing the nose down into a steep dive. This is indubitably one of the type-universal "no checklist required" responses to depressurization and totally quintessential for survival. Unfortunately, and likely unbeknownst to them, they actually had no oxygen from their masks as a fallback ... and so they lapsed into unconsciousness and the airplane zoomed back to height. If MH370 stalled, it would've recovered easily via its Active Flight Control System and thus commenced its ghost flight. Those aft of the locked flight-deck door would've continued to breathe until their limited oxygen supplies were exhausted. And so the POB remainder in the cabin would've expired over the next few minutes (but not hours), quite unaware of the brief dramatic fire that had "taken out" their flight-crew... on the other quite invisible side of that divisive, encapsulating and impenetrable door.
We can be reasonably sure that there have historically been a number of such accidents attributable to oxygen-induced fire in an airborne environment - but just like electrical wiring fires, the residual evidence is almost invariably consumed - and the finding is almost predictably indeterminate - or non-deducible. The incongruity (and oft-denied fact) is that that a pilots' repository of life-giving oxygen can both sustain and destroy. Sometime Life gives, oft-times it subtracts. Could the oil-rig operator have seen that 5 to 10 second flash-over from a distance? Courtesy of empty-field myopia, which allows one to see great distances at night if you've something to focus upon - that bottom-line verdict might be "conceivably". Like any scenario that relies upon vacuous triggers, theoretical effects and thresholds, the oxygen flare theory is contestable ... but nevertheless, it overall fits the bill for that MH370 backdrop. Ample precedents also serve to endorse the case for MH370 having been an oxygen inspired fire event.
So you be the judge. Did the investigators of any of the preceding oxygen-fed ramp fires (777, 767, P3 etc) sufficiently extrapolate the danger potentials into an airborne fire circumstance? Did they act conscionably to address the threat - or did they miss their cue altogether? No need to even "rest that case". There is a sufficiently vigorous argument for this particularized MH370 scenario. i.e. it fits the bill of known developments and timings. As is so often the case, the regulators (in turn) just "blew it" - and preserved the threat intact. But because that MH370 victim airplane then ploughed on and "withered in the wind", the regulators and manufacturers yet again get to patch over their lack of oversight ..... and so, for families in search of "closure", an uncomprehended misery must always replace any possible certainty. Surmise is never enough. Plausible explanation may be accepted - but acceptance without evidence is always so counterfeit to the many.
The oxygen flare fire answer for the victims' families would always be "bitter-sweet" (i.e. those MH370 pax almost provably never suffered, they just "expired" without any discomfort). Such is the nature of persistent extreme hypoxia.
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https://www.youtube.com/watch?v=Aol_h_-24bs
https://www.youtube.com/watch?v=vV3mzluqHig
https://www.youtube.com/watch?v=OMOGaugKpzs