Comment by dwohnitmok | Hacker News Reader

Comment by dwohnitmok | Hacker News Reader

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I don't know much about the Hindenburg disaster, but the fact that it is difficult to set something alight with bullets traveling through a thin fabric and then (flammable) air (as opposed to having sparks generated by bullets hitting e.g. metal and even then, there's not a lot of sparks) is not really evidence of hydrogen's safety. It's really really hard to make even normally flammable things catch fire with normal bullets or even tracer bullets. You could shoot at a gas tank all day and it won't explode. Even absolutely riddling a gas tank with tracer rounds often won't set it alight. It is far far far easy to set something alight with a single match than it is even with full magazines of bullets, all the more so if it's a patch of air that the bullet goes straight through.

Hydrogen is still widely acknowledged to be extremely flammable (see all the references here https://en.wikipedia.org/wiki/Hydrogen_safety). We have had many many disasters with hydrogen explosions pre and post-Hindenburg.

> to having sparks generated by bullets hitting e.g. metal and even then, there's not a lot of sparks

Just wanted to chime in on this - it's impossible for most bullets to cause a spark, unlike what TV and movies show. Most projectiles (including the .303 round the British were using back then!) are lead with a copper plating, which are both non-ferrous metals.

Some Soviet era and US military ammunition (specifically m855 rounds) have a steel core, and those can cast sparks, but almost all handguns, and most rifles, aren't using ammunition capable of doing do.

The reason for this is that the bullet has to be made of a softer material than the barrel, or else the barrel would wear out really fast.

Sparks no, but a spall can be hot. Fabric will not spall but whether by spark or spall, bullets hitting solid objects can generate enough heat to ignite things they touch.

Ah yes you're totally right! I suppose the majority of fires I've seen have been caused by spalling or something similar as sandworm101 points out.

Note that regardless of what you do, a container of fuel (without its own oxidizer) would never successfully light/sustain fire without first having displaced the majority of the fuel with atmospheric air to provide the necessary oxidizer. That’s why you can’t light a full container even with tracer rounds.

Otherwise, you are only be able to light the part of the fuel that leaked into the atmosphere.

I think people have done experiments with gasoline exposed to open air or with a chamber of air and even then it is quite difficult to ignite, especially if the bullet has nothing to impact against, but travels through the vapor.

This is interesting to contrast with my experience as a former tank commander doing range gunnery with wooden targets and dry brush. Range fires due to machine gun fire happened all the time. They were not remotely uncommon or difficult to cause.

I know next to nothing about chemistry or materials science, so offer no explanation of why this would be the case but a gas tank is difficult to ignite. The only layman intuitive answer I can think of is that a high speed projectile traveling through wood generates a lot more friction than one traveling through a liquid or gas, and something has to happen to that energy.

Yeah as soon as you have a solid chunk of something to hit it's a lot easier to start a fire. E.g. it's actually quite easy to start a fire by shooting a lot of bullets into a gas station pump rather than a thin barrel.

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