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I’ve also seen reports of grain silos in the area being destroyed; grain is an astonishingly powerful explosive.

throwaway0a5e 6y ago
Grain is a pretty poor explosive because the upper and lower explosive limits are so close (yes I know that's not traditionally a metric we use for solids), it needs an oxidier and the volume of byproduct for volume of input is relatively low. But large amounts of grain and oxygen are often found together in confined spaces so that makes it more explosive in practice than most things that people who work in offices and don't deal in bulk goods come into contact with.
- throwaway_pdp09 6y ago
  Can you elaborate what "upper and lower explosive limits" are, please. Also I don't understnd how it could be explosive at all, sudden oxidation of large (that is, low surface area to volume), non-dry particles seems unlikely. Flour etc. may be another matter, but a blast like this... flour?
  - throwaway0a5e 6y ago
    >upper and lower explosive limits concentration of the fuel in otherwise normal atmospheric air required to go whoosh (or bang, which is basically just a really fast woosh or one that's constrained by something). Too much fuel, too rich, no woosh. Too little fuel, too lean, no woosh. Lower and upper explosive limits are generally used to refer to gas mixtures though you can use them for solids but the units will be different. Solids we think of as explosive when not fishing around for virtue points on the internet generally contain their own oxygen supply so lower and upper explosive limit doesn't apply. >sudden oxidation of large (that is, low surface area to volume), non-dry particles seems unlikely. Flour etc. may be another matter, but a blast like this... flour? Yeah, no way that secondary explosion is flour or grain. I'd put my money on some sort of industrial chemical that contains its own oxidizer. Explosions that use atmospheric oxygen look different and rarely manage to be able to build up that kind of shock-wave if not constrained by something (like a building). There should be videos of natural gas explosions on YouTube that illustrate the difference.
  - TimSchumann 6y ago
    Most grain elevators have incredibly large quantities of dust (basically flour) lying around, it's just unavoidable when you're moving that much grain around. If it's too dry, there's a risk of static/friction/electrical ignition. If it gets wet, you can have anaerobic bacteria build up heat in a compartment that, when exposed to oxygen, ignites. Grew up on a farm, have a fair bit of experience messing around with grain bins. Our local elevator had a fire due to the former condition, and our neighbor's barn burned down due to the latter.
- vidanay 6y ago
  If there was a large enough explosions to blast the grain silos into the air and disperse the grain, it could find that "perfect" balance at some point and then flash over.
jcranmer 6y ago
The first fire (pre-big-explosion) clearly is taking place in a warehouse next to the grain silos. The big explosion appears to take place in the same warehouse as well. A single frame of the fireball shows a large spherical fireball whose edge maybe reaches the edge of the grain silos. The next frame looks to my untrained eyes more like the edge of the fireball is having some reflection from the wall of the grain silos, followed by a dark cloud obscuring details, and then the vapor cloud really obscuring everything, and finally the photographer falling over. It seems pretty clear to me that grain played no role in the big explosion.
eitland 6y ago
I really feel sorry for the Lebanese people today. They were in a tough spot already before this happened :-/

Grain is a pretty poor explosive because the upper and lower explosive limits are so close (yes I know that's not traditionally a metric we use for solids), it needs an oxidier and the volume of byproduct for volume of input is relatively low. But large amounts of grain and oxygen are often found together in confined spaces so that makes it more explosive in practice than most things that people who work in offices and don't deal in bulk goods come into contact with.

throwaway_pdp09 6y ago
Can you elaborate what "upper and lower explosive limits" are, please. Also I don't understnd how it could be explosive at all, sudden oxidation of large (that is, low surface area to volume), non-dry particles seems unlikely. Flour etc. may be another matter, but a blast like this... flour?
- throwaway0a5e 6y ago
  >upper and lower explosive limits concentration of the fuel in otherwise normal atmospheric air required to go whoosh (or bang, which is basically just a really fast woosh or one that's constrained by something). Too much fuel, too rich, no woosh. Too little fuel, too lean, no woosh. Lower and upper explosive limits are generally used to refer to gas mixtures though you can use them for solids but the units will be different. Solids we think of as explosive when not fishing around for virtue points on the internet generally contain their own oxygen supply so lower and upper explosive limit doesn't apply. >sudden oxidation of large (that is, low surface area to volume), non-dry particles seems unlikely. Flour etc. may be another matter, but a blast like this... flour? Yeah, no way that secondary explosion is flour or grain. I'd put my money on some sort of industrial chemical that contains its own oxidizer. Explosions that use atmospheric oxygen look different and rarely manage to be able to build up that kind of shock-wave if not constrained by something (like a building). There should be videos of natural gas explosions on YouTube that illustrate the difference.
- TimSchumann 6y ago
  Most grain elevators have incredibly large quantities of dust (basically flour) lying around, it's just unavoidable when you're moving that much grain around. If it's too dry, there's a risk of static/friction/electrical ignition. If it gets wet, you can have anaerobic bacteria build up heat in a compartment that, when exposed to oxygen, ignites. Grew up on a farm, have a fair bit of experience messing around with grain bins. Our local elevator had a fire due to the former condition, and our neighbor's barn burned down due to the latter.
vidanay 6y ago
If there was a large enough explosions to blast the grain silos into the air and disperse the grain, it could find that "perfect" balance at some point and then flash over.

jcranmer 6y ago

The first fire (pre-big-explosion) clearly is taking place in a warehouse next to the grain silos. The big explosion appears to take place in the same warehouse as well. A single frame of the fireball shows a large spherical fireball whose edge maybe reaches the edge of the grain silos. The next frame looks to my untrained eyes more like the edge of the fireball is having some reflection from the wall of the grain silos, followed by a dark cloud obscuring details, and then the vapor cloud really obscuring everything, and finally the photographer falling over. It seems pretty clear to me that grain played no role in the big explosion.

eitland 6y ago

I really feel sorry for the Lebanese people today. They were in a tough spot already before this happened :-/