TEIF: Behind the scenes

Failure of the Crew Module

The forensic evaluation of all recovered crew module/forward fuselage components did not show any evidence of over-pressurization or explosion. This conclusion is supported by both the lack of forensic evidence and a credible source for either sort of event. The failure of the crew module resulted from the thermal degradation of structural properties, which resulted in a rapid catastrophic sequential structural breakdown rather than an instantaneous “explosive” failure.

Separation of the crew module/forward fuselage assembly from the rest of the Orbiter likely occurred immediately in front of the payload bay (between Xo576 and Xo582 bulkheads). Subsequent breakup of the assembly was a result of ballistic heating and dynamic loading. Evaluations of fractures on both primary and secondary structure elements suggest that structural failures occurred at high temperatures and in some cases at high strain rates. An extensive trajectory reconstruction established the most likely breakup sequence, shown below.

The load and heat rate calculations are shown for the crew module along its reconstructed trajectory. The band superimposed on the trajectory (starting about 9:00:58 a.m. EST) represents the window where all the evaluated debris originated. It appears that the destruction of the crew module took place over a period of 24 seconds beginning at an altitude of approximately 140,000 feet and ending at 105,000 feet. These figures are consistent with the results of independent thermal re-entry and aerodynamic models. The debris footprint proved consistent with the results of these trajectory analyses and models. Approximately 40 to 50 percent, by weight, of the crew module was recovered.

The Working Groupʼs results significantly add to the knowledge gained from the loss of Challenger in 1986. Such knowledge is critical to efforts to improve crew survivability when designing new vehicles and identifying feasible improvements to the existing Orbiters.

Crew Worn Equipment

Videos of the crew during re-entry that have been made public demonstrate that prescribed procedures for use of equipment such as full-pressure suits, gloves, and helmets were not strictly followed. This is confirmed by the Working Groupʼs conclusions that three crew members were not wearing gloves, and one was not wearing a helmet. However, under these circumstances, this did not affect their chances of survival.

tlb wrote:

kzt wrote:Most people tend to find that breathing is really, really important and doing things that allow you continue breathing tends to be top of mind. Particularly when you are not trying to, say, get the hydraulics back on line.

You are correct that NASA claimed that they "probably survived the initial breakup of Columbia, but lost consciousness in seconds after the cabin lost pressure". The statement from the following website does not state how much destruction or violent motion was occurring as the cabin lost pressure, but it was certainly much too late to "get the hydraulics back on line".

Jonathan_S wrote:But note that while you might lose consciousness within seconds of exposure to hard vacuum, and hypoxia might impair you enough to prevent taking effective action to save yourself even quicker, neither of those should be an issues in the aftermath of a thermobaric explosion.

Its vacuum should only last seconds total, and you don't need to take effective action to continue to survive that "vacuum" because it'll clear itself (by the returning inrush of displaced air reestablishing the pressure equilibrium) by the end of those few seconds.

Now Hypoxia and unconsciousness can be deadly at high altitudes or vacuum conditions where you need to take quick, correct, actions to restore the oxygen or atmosphere in order to save your life. Lose the ability to perform those and you're done for, even if actual death takes a bit longer.

Jonathan_S wrote:why focus on the the vacuum rather than on their asphyxiating effect if used in enclosed, low airflow, spaces (like caves)? Unlike a regular explosive the thermobaric FAE consumed lots of atmospheric oxygen as oxidizer for its fuel -- in an enclosed space that wasn't blown open by the explosion that could so deplete the oxygen that survivors might asphyxiate before natural air exchange replaced the excess CO2 with fresh O2.

tlb wrote:

Jonathan_S wrote:But note that while you might lose consciousness within seconds of exposure to hard vacuum, and hypoxia might impair you enough to prevent taking effective action to save yourself even quicker, neither of those should be an issues in the aftermath of a thermobaric explosion.

Its vacuum should only last seconds total, and you don't need to take effective action to continue to survive that "vacuum" because it'll clear itself (by the returning inrush of displaced air reestablishing the pressure equilibrium) by the end of those few seconds.

Now Hypoxia and unconsciousness can be deadly at high altitudes or vacuum conditions where you need to take quick, correct, actions to restore the oxygen or atmosphere in order to save your life. Lose the ability to perform those and you're done for, even if actual death takes a bit longer.

That's a very interesting point that I had not considered. For an air-fuel explosion in a cave or other constricted environment with poor ventilation, this needs to be amended by your earlier statement:

Jonathan_S wrote:why focus on the the vacuum rather than on their asphyxiating effect if used in enclosed, low airflow, spaces (like caves)? Unlike a regular explosive the thermobaric FAE consumed lots of atmospheric oxygen as oxidizer for its fuel -- in an enclosed space that wasn't blown open by the explosion that could so deplete the oxygen that survivors might asphyxiate before natural air exchange replaced the excess CO2 with fresh O2.

cthia wrote:If anyone is injured and has to fight for air that has been knocked out of them is inhumane. A quick kill isn't inhumane. Someone who is frail or sick and experiences the effects at the right time can suffer a collapsed lung.

cthia wrote:I have traveled a lot. Even here in the US. I know a lot of doomsdayers. They have fashioned elaborate underground bunkers. A fuel cloud might not penetrate an underground bunker, but the vacuum could affect it.

I worked for a turbine company and I had the unpleasant opportunity to experience a wind tunnel. And trust me, that is not pleasant, but it is a piece of cake comparatively. If anyone is injured and has to fight for air that has been knocked out of them is inhumane. A quick kill isn't inhumane. Someone who is frail or sick and experiences the effects at the right time can suffer a collapsed lung.

Do consider that these type weapons were fashioned for a particular situation of flushing the enemy out of caves. Varying terrain might blunt the effectiveness.

Jonathan_S wrote:

cthia wrote:I have traveled a lot. Even here in the US. I know a lot of doomsdayers. They have fashioned elaborate underground bunkers. A fuel cloud might not penetrate an underground bunker, but the vacuum could affect it.

I worked for a turbine company and I had the unpleasant opportunity to experience a wind tunnel. And trust me, that is not pleasant, but it is a piece of cake comparatively. If anyone is injured and has to fight for air that has been knocked out of them is inhumane. A quick kill isn't inhumane. Someone who is frail or sick and experiences the effects at the right time can suffer a collapsed lung.

Do consider that these type weapons were fashioned for a particular situation of flushing the enemy out of caves. Varying terrain might blunt the effectiveness.

Barring something really weird, if the external 300-400 PSI overpressure can't get in and cause damage you've got even less to worry about an external vacuum that lasts for, at most, a second or two. The same restrictions that kept the overpressure out should dramatically limit how much of the bunker's air can flow out in those few seconds before the outside reestablished the normal air pressure equilibrium.

This is related to why (Hollywood nonsense not withstanding) a bullet hole in a pressurized airplane doesn't cause explosive decompression that immediately incapacitates everyone. Compared to the amount of air the the plane the hole is very small and even with a significant pressure differential the rate of air loss through it is pretty low. (Actually, a airliner is normally turning over the entire volume of cabin air every 2 - 3 minutes; venting it out an exhaust port and replacing it with freshly compressed and filtered air from the engines -- that's how the cabin air is kept fresh through the flight. That exhaust port is way larger than a bullet hole and they'd just need to adjust that port's constriction slightly to balance the air lose from the bullet hole)

A well designed bunker is going to be fairly well sealed off from the outside atmosphere, and the rate at which a vacuum (which, remember, can exert less than 14.7 PSI of pressure delta to move the air) is going to be able to remove the internal air back through gaps around the seals, or through the air filtration and exhaust system is going to be pretty slow. (And as the pressure in the bunker drops the rate at which additional air is lost also slows down)
So the transient vacuum created by the fuel air explosion is going to dissipate long, long, before any meaningful amount of air can escape the bunker.



Sure if you could, by magic, instantly drop the entire bunker's air pressure down to, say, 1 PSI and keep it there for a couple minutes the folks inside would die; and in a pretty nasty way. But that's just not going to happen as the result of any outside explosion.