calculating pressure at a certain distance from an explosion

[18medic]

I’m looking for an equation to figure out the pressure of an explosion from a given distance from that explosion. I’m in the Army and I'm currently deployed to Afghanistan. I’m trying to let my unit understand the science behind and explosion from an improvised explosive device. We are driving around in V shaped hulled vehicles, but I want to try to keep them informed on how close the IED has to be to destroy things, and how keeping a good distance (like driving in the middle of the road) will minimize the damage. Basically they are using items that contain between 1 and 5kg of c-4, like anti-tank mines and mortar rounds. Basically I want to figure out how much pressure is lost every foot from the point of detonation of 1-5kg of c-4. If you could help educate me so I can let others know I would be very thankful.

 

[IRstuff]

There's no simply answer, beyond the simple fact that the pressure falls inversely with the distance squared. That said, the explosive effects are highly dependent on the surroundings and how the explosion is generated.

A good example is normal black powder found in a firecracker. By itself, it simply burns extremely fast, but when confined in a simple roll of paper, that tiny amount can easily remove one or more fingers, or destroy your eye.

As you are well aware, IEDs and HMEs are packaged differently by different people, so the blast effects are highly variable, ranging from a straight explosive blast, to something with lots of shrapnel, to something that could even damage an MRAP.

The best you can hope for is to be vigilant and exercise due caution and follow whatever best practices you have.

Be safe, and good luck.


TTFN

FAQ731-376

 

[rmw]

Your logic is right, but unfortunately you are not dealing with firecrackers here. The same firecracker that will take a finger off when held in the fingers won't hurt you too bad if you can throw the firecracker even just a few inches away from your hand. I have done it both ways and had them go off just inches, like 3-4 from my fingers, and in my hand, fortunately never at the expense of a finger, but at the price of some significant pain.

The majority of the IED's that you are dealing with are stong enough that if you or your vehicle are close enough to set it off you are too close already, no matter how far from it you have gotten by your driving technique. That doesn't mean that no precaution is called for, however. An ounce of prevention....

Sorry to say that and only can say stay safe by being other wise diligent. Judging by your handle above, I hope that you only get to ply your trade for scrapes and bruises only.

rmw

 

[MrShaff]

Hi 18medic

I am a physical security consultant in Israel and will try and answer your questions, remembering that a lot of factors will affect the pressure of the blast, like the shape of the device, the angle, the detonation etc....Using TNT as an example

3kg at 1m will give a pressure of 20126 kPa and an impulse of 2119 kPa-ms, which is huge

3kg at 2m away drops the pressure to 3201kPa and an impulse of 830kPa-ms - notice the massive difference of just 1m

3kg at 3m away and your pressure is 938kPa and impulse of 500kPa-ms

These pressures are using a software called WINDAS and specifically is used to measure blast loads against glazing, but the pressures are the pressures - so the further away you are, the better.

By the way, a 400ton explosion at 50m away gives a reflected pressure of 21118kPa and an impulse of 111636kPa-ms - crazy..but the actual reflected pressure is similar to the 3kg of TNT at 1m standoff

If i was you i would do searches on internet for standoff distance from blasts etc... have fun!

 

[jmw]

I recall from my ROC days we had a very basic sensor in our bunker called a BPI or blast pressure indicator. OK so this was for nuclear explosions but the principle is the same.
Basically just a very simple pressure sensor which will indicator the maximum pressure from a blast.
It seems to me that the Military, experiencing the problem from IEDs, would find it useful to fit some simple sensors on the vehicles inside and out so they can build a picture of the sort of blasts they have to contend with.
Coupled with various simple measurements I would have though this could be very valuable information.

How expensive can that be?
How valuable?

JMW

http://www.ViscoAnalyser.com