About how far away would you need to place a block of C4 (without a detonator) so that detonating another block of C4 (assume a 0.5 Kg block, set 1 meter above the ground) wouldn’t set it off? (Assume the only thing between them is air, altitude is ~100ft above sea level (or whatever number is used as normal, if there is one), and relative humidity is ~60% (or whatever the average humidity would be on a bomb range).
I’m guessing there’s a formula for this, but I mostly want to get an idea for the scale. Is it closest to: [ol]
[li]a few feet[/li][li]1 - 10 few yards[/li][li]a dozen yards[/li][li]several dozen yards[/li][li]hundreds of yards[/li]or does it hit numbers where you’re being shielded by the curve of the earth [/ol]
From a publicly available paper like this one from 2013, it looks like #2 is far enough. From the paper, it depends on how the blast is propagated from the first charge (“donor” in the paper) to the second charge ("acceptor): having only air between the two really attenuates the shock impulse, whether the donor is bare, or is throwing fragments at the acceptor, etc… For 60mm diameter charges of RDX+Aluminum, encased in 3mm thick steel, placing the charges 300 mm away removed most of the risk of even deflagration. Weird, I’d have thought it was a lot further, but that’s what they found.
Anyway, the paper gives lots of cites to further your research.
EDIT: also look at the regulations for explosives magazines and allowable distances between them. This was just what I found quickly.
D=K*cube root of the net explosive weight.
To prevent mass detonation from an above ground explosion of mass detonating material such as C-4, the K factor is 11. The NEW for a block of C-4 (standard US Army issue M023) is 1.25 lb.
Doing the math D in feet from one block of C-4 to another with nothing in between is
11.84939 feet.
You could add in the contribution from a standard US M6 electric blasting cap at 0.002930 lb. to the original weight but we are getting pretty fine.
No frag from a block of C-4, it’s only got a mylar wrapper and some double sided tape.
As long as the blocks are more than a few inches apart and the blast is not confined, just the gap boundary between the blocks is probably enough to ensure that the second uninitiated block does not detonate (or, at least will not reliably detonate). C-4 is actually quite stable to the point that a mechanical shock alone will not set it off; it requires a very energetic shock along with high temperature provided by a powerful initiator (larger than a standard “blasting cap” used for commerical blasting emulsions). I suspect that even a few centimeters of separation would be enough to reduce the input energy below the critical energy fluence (the amount of energy per unit area required to assure the detonation condition). This is why when setting demolition charges, detonators or boosters are put into every explosive element in the explosive train. In the case of building demolition, two detonators or boosters are typically installed to ensure that no explosive element goes undetonated or incompletely detonated, as the last then you wnat when you’re clearing the demo site is to come across unexploded ordnance.
