Originally Posted by Empty Cruise
chornedsnorkack,
As an ex-firefighter, experience (and some long forgotten theoretical stuff) tells me that yes, pressure will make a difference - put partial pressure i.e. how much of that pressure is made up by oxygen, only takes effect at higher altitudes.
If you lower the pressure without changeing the partial pressure, e.g. by ventilating, the fire will flare (fair 'nuff, since lower presure will mean higher evaporation-rate = more gasseous contents in air = fire flares). Likewise, if you increase pressure by e.g. directing waterfog above the fire, you get a sh#tload of steam out of it (the figure 1680 ltr. steam per litre of water that evaporates completely springs to mind - anybody?). The generation of steam will both take a lot of the heat out of the fire and increase pressure, thereby smothering the fire.
I doubt that pressure is changed in either case. After all, in uncontained spaces any change of total pressure would blow away very quickly and forcefully. Only in an intact fuselage is pressure a variable...
Originally Posted by Empty Cruise
Re. staying in one piece on ditching - well,
afaik all aircraft with pod-mounted engines have shear-bolts in the struts that will allow the engines to break away rather than break up the wing on contact. The fuselage - depends on sea-state, wind direction & strength, if power & hydraulics are available before impact or not, and the skill of the crew. If all goes according to plan, see no reason why you shouldn't be able to keep fuselage fairly intact, and that should lead to a much more orderly evac, improving long-term survival chanches. But when you think of how willing some of the punters are to follow CC instructions, some will still try to swim to distant land, some will only cling to their family, some will overinflate their lifejackets, some will take off clothes in the wather, and some will not want to float face down in high winds. These people will die anyway within the first 15-20 minutes
PS - how many have practiced the ditching manoeuvre within the last 36 month sim-cycle? Some airlines seem to take it seriously, others adopt the "Nah, you'll never need it - here's another EFATO for you"-attitude.
Empty
Do the simulators give realistic outcomes about airframe breakup and occupant safety?
So, while the airplanes can supposedly be made safe against engine fires and also can be proofed against belly hold fires, they cannot be protected against cabin/cockpit fires...
What does the belly hold safety rely on? Halon bottles?
These supposedly work by interrupting radical chain reaction, and do absolutely nothing about exothermic reactions from other reaction mechanisms... like lithium fire.
I can see a simple physics reason why no plane can be safe against post-crash fires (it carries a lot of fuel, for example Boeing 747-400ER has 240 000 litres, about 200 tons, except naturally if crashing due to fuel exhaustion).
But before crashing... the hold of Boeing 747-400ER is about 160 000 litres volume. Minus the cargo contained, of course. On sea level, 160 000 litres air weighs about 200 kg, if I get it right, and including about 50 kg oxygen. These numbers decrease by about one quarter in cruise and, back-of-the-envelope, to 40 % original value if the fuselage is decompressed to 25 000 feet.
If there is a fire in a cargo hold, does fresh air continue to enter the cargo hold, and does smoke and flames get to cabin and cockpit?