Jonathan_S wrote:But that low pressure area is pretty transient -- only long enough for the blast wave to exhaust itself, over expand, and collapse back in. We're talking a handful of seconds since the explosion -- and humans can survive exposure complete vacuum for that long without significant injury. (And of course to closer you are to the point where the pressure wave finished over expanding and revered the smaller the pressure difference behind it is -- so if you're far enough away that the overpressure didn't get you the underpressure's not going to either)
Loren Pechtel wrote:Minor disagreement. Humans can survive a short exposure to vacuum without injury, but we can not survive an instant's exposure to vacuum. While the lack of air itself only does meaningful harm from a lack of oxygen the sufficiently sudden loss of the air inflicts lethal lung damage.
From a practical standpoint I would think the only risk from low pressure would be to those inside the zone but not exposed to the blast front. Say, somebody in a hole in the ground. I have never seen information on how big the threat is.
cthia wrote:Exactly! Instant vacuum, and without warning, just after having the wind knocked out of you.
I think the picture we should have in mind is the video from the old A-bomb tests, where first the trees bend away from the bomb as the initial blast front passes over and then the trees bend back toward the bomb site as air rushes back to fill the low-pressure area.
The problem with the previous formulation (aside from a confusing use of "vacuum" twice when one should perhaps have been "oxygen"), is that the low pressure wave is the rebound part of the blast wave, they are not separate entities. So unless there is a specific distance where the high-pressure part of the blast front is survivable, but the low-pressure part that follows behind is not; then this should not occur (however KZT says this is not the case, instead the low-pressure has minor effects compared to the high-pressure). I think that you have to be pretty far from the bomb site before you can hide from the blast front in a hole; specifically if the low-pressure behind the blast front is enough to hurt you, then the blast front is going to do much more than just knocking the wind out of you - even in a hole.
I recall that there was a NASA employee at a test facility that was exposed to a nearly complete vacuum and survived. From
Popular Mechanics:
In the mid-1960s, everyone at NASA was gearing up to go to the moon. The unmanned Apollo test flights would begin in 1967, with manned flights the following year. But long before any components or astronauts when to space, every aspect of spaceflight had to be thoroughly tested by NASA engineers.
One of those tests involved how well pressurized spacesuits would perform in the vacuum of space. For these tests, NASA constructed a massive vacuum chamber from which they could pump out all the air. One of those tests, involving test subject Jim LeBlanc, did not go so well.
During the test, the hose that supplied air to his suit became detached, and LeBlanc was exposed to the effect of the vacuum for about 30 seconds. Fortunately, he was rescued from the vacuum chamber with almost no injuries, but if his rescuers had taken a little longer to reach him, he could have suffered severe health effects.
