Hi All, very interesting analysis and discussion!
So bearing the following in mind:
- This is just Ammonium Nitrate (not properly mixed ANFO) in an unknown condition.
- The fire at the north end of Warehouse 12 is assumed to have initiated the explosion.
- From photos the 1000KG bags of AN were stacked 2-3 high and haphazardly throughtout what appears to be a fairly spacious warehouse.
- ANFO is notoriously difficult to initiate and without the a fuel component mixed througout the entire mass, and may not fully burn. This will probably decrease the yield considerably with straight Ammonium Nitrate.
My question is, looking at surface detonations from non-kinetic explosive devices it appears that the crater is far too large for the proposed yield.
I don't pretend to be able to check your calculations and the methodology looks thorough and any assumptions, reasonable.
Using this crater-size calculator, I changed the explosive type to ANFO and, the surface to Hard Soil/Dry Soft rock and set the yield to 2700 tonnes.
http://keith.aa.washington.edu/craterdata/scaling/index.htm
The tool produces a crater rim diameter of 60m whick explains the crater daimeter not the length of 120m.
The problems therefore appear to be:
- An actual explosive was used in the calculation where in reality we had an oxidiser and some fuel.
- The fuel and oxidiser were not uniformally mixed and therefore as above the yield cannot be 2700 metric tonnes.
- Reducing the probable yield your upper end of 400 tonnes produces a rim diameter of 35m
- Changing the surface material to 'dry soil' at a 400 tonne yield produced a 55m crater which is close the diameter but half the length of the actual crater.
With the Beirut crater length of 122m and the width half that at about 60m, we cannot model this even with the full yield using ANFO (correctly mixed, expected nitrogen levels, no contaminants).
Of course I have only changed several parameters and I don't know what that particular port quay was made from (mixture of concrete, bed rock, hardcore) with a surface load bearing limit somewhere in 30-50 tonnes per quare meter.
This leads me to thinking that some of the following may be valid:
- The quay was very weak and a significantly larger crater could be created with a maximum 400 tonne yield but even if it was contructed with dry soil we can't get anywhere near 120m.
- Explosive force distribution was abnormally biased downwards somehow? Could the 1000kg AN bags have been stacked by accident to create a shaped charge?
- Some of the AN was stored underground but would place it potentially at or under sea level which doesn't make sense. However with dry sand with some of the explosives under the surface we can only get a crater size of 83m.
Of course there are quite a number of variables/unkowns here and even if the tool is reasonably accurate, it appears that the crater is too big for the yield.
One final thought around AN initiation, it appears that the risk of explostion increases with the level of confinement. Was the confinement level in this warehouse enough to get this amount of bang from nearly 2700 tonnes of hapahzardly stored AN?
Any thoughts guys?
