The blast lab

How much damage can an explosion cause and how can we measure it?
07 July 2015

Interview with 

Dr Bill Proud, David Sory, Imperial College London


How much damage can an explosion cause and how can we measure it? bomb damageExplosives researcher Bill Proud is developing techniques for testing how different materials respond to the shock waves caused by a blast. He even has a device that uses donated human body parts to help him to understand the injuries that can be sustained in an explosion. Bill and his PhD student David Sory showed Tom Crawford around their bomb lab...

Tom - Here we are at Imperial or more precisely, the physics laboratory and right on cue here is the man of the hour, Bill Proud. Very nice to meet you, Bill.

Bill - Hello.

Tom - I'm a bit of a pyromaniac so I'm itching to get started. Should we head inside?

Bill - Well, on the hottest day of the year, that's a good idea.

Okay, so we're going into a laboratory environment. So appropriate safety equipment must be worn. So, here's your lab coat.

Tom - It's a little big. Okay, safe as houses. We've just entered the lab and it kind of reminds me of being back at high school in chemistry to be honest. There's lots of cabinets. I can see some things that look like fume cupboards... Oh, and here we go, there's a very long tube-like device which I assume is what we're going to be firing.

Bill - This device, the split-hopkinson pressure bar. It's a device that does compressive loading on samples. Compression meaning you're squeezing them to be shorter than they would normally be. The kind of pressures we're introducing here are over the time periods of say, 100 microseconds. So, 100 millionth of a second. That doesn't sound like a very long period of time, but that's certainly more than enough time to fracture bones, destroy metal, break ceramics. The advantage of this device is it has a very clean on, off pressure pulse. And that has advantages in making the results easy to analyse.

Tom - But when you're looking at ceramics and metals, is that to sort of advise which building materials should be used, what kind of material should be used in protective equipment for example?

Bill - That's true. We are looking at the human body. We are looking at the thing the human body is in contact with. So, if you think of body armour, if you think of clothing, if you think of shoes, all of those have a mixture of combinations of polymers, foams, ceramic faces to buildings, the metals that are used in vehicles.

Tom - David, has very kindly or perhaps very stupidly said that I can have a go at firing this thing myself. So, what do I do?

David - You just press on the boom button.

Tom - I'm a little scared about this, but let's give it a go. Do you think you can count me down?

David - Firing in 3, 2, 1...shooting!

Tom - What you've just heard was the sound of a short metal rod, not too dissimilar to a bullet, being fired along a 1-meter long tube into a series of aligned metal rods. The samples being tested are placed in between these metal rods where sensors are positioned to record the response of the sample to the blast wave. This is all great fun Bill, but what do you actually learn from these experiments?

Bill - The aim of the Royal British Legion Centre for Blast Injury Studies is to understand the mechanisms of blast injury on people, what kind of injury pattern they will get, how to mitigate against that kind of injury and also, to understand the long term pathology. This means, how people recover from blast injury.

Tom - What kind of injuries could occur as a result of a blast?

Bill - The human body has a lot of air-filled cavities in them. We're talking about the ears. They're the most blast sensitive organs we have. Then you get problems with your larynx. But the other and largest and most obvious part of the human body are the lungs. You have conditions called blast lung where people are exposed to blast wave and immediately afterwards, they feel okay. But over a period of days, their health will decline and if adequate treatment is not given, ultimately, many of them can die. There's also a whole area called solid blast where metal plates, solid objects, they push on the human body and can produce very severe injuries.

Tom - I'm getting a feeling that might be where we're going next.

Bill - Yes, you'd be completely right.

Tom - So, where on earth have you brought us now, Bill? We've been down about 10 flights of stairs through 6 secure doors. What's going on?

It's a completely white room, much bigger than the previous lab. Everything looks very clean and we've been instructed not to touch any of the surfaces.

Bill - So, we're in the very basement of the Royal School of Minds in Imperial College London and we're in a room that we house a device called ANUBIS. ANUBIS stands for An Under-Belly Impact Simulator.

Tom - It's like a rectangle made out of metal girders and in the centre of this rectangle is some kind of structure poking upwards which is housing some kind of large steel drum which I would assume is the thing that's going to move and cause the blast. Is that correct?

Bill - The large steel drum is the pressure vessel and on top of that there's a metal plate. That metal plate can be accelerated at velocities of up to 30 meters a second. We would use this for testing what you might call structural components. So, that could be, for example, legs.

Tom - Do you mean like, actual human legs?

Bill - Instead of doing studies on say, animals and then trying to extrapolate that to people, we can do work on human tissues. So yes, human legs and therefore, we can understand directly what the effect is. 

Tom - By using actual human tissue in the lab, Bill and his team are able to reproduce the same conditions seen in the field, for example in Iraq or Afghanistan. This is verified following an experiment by a  military medic with first-hand blast injury experience.

During the experiment, measurements are made of the exact forces felt by the human tissue, which along with high speed video camera imaging, allow the scientists to see exactly where and how the bones and soft tissues begin to break and tear in an impact. Pinpointing these locations is key to understanding where the forces are concentrating and therefore where the injuries start. This data can then be used to design protective equipment to try to prevent injury.

Bill - All of these human tissues are donated by people, when people donate their bodies to medical science for example. But it's very important that we have that type of material to work with because this means we can stop guessing of how an animal corresponds to a person. We can go, "This is what happens with the person."

Tom - Yeah, nothing beats the real thing.

Bill - In a way, yes.

Kat - I thought they were going to blow up an actual human leg there for a moment. That's Bill Proud and his PhD student, David Sory from Imperial College London.


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