A loud, sweeping sound comes from the nearest industrial plant, and it’s unmistakable that there’s been an explosion. The police and the fire service are already on the scene, working diligently to ensure that nobody nearby has been seriously injured; and to clear way any potentially dangerous debris. At home, your iPhone starts buzzing. It’s time to put down that cup of tea and the coveted “Forensic Analyst of The Year” invite you hold in your hands — we’re about to embark on some of the most daring work forensic science offers.
Scene security and preventing contamination
First things first, the scene: good old (not so common) sense applies here. Make sure what’s left isn’t likely to combust or collapse around you and ensure there is some structural integrity to whatever construction you’ll be walking inside. Leave this to the professionals – you may be an action man but in this case, chances are the bomb squad are more likely to know what they’re doing. We need to make sure we’ve got it properly secured, and then call in the photographers to snap up whatever remains — thereby preventing any questioning later that someone, well meaning or otherwise, trampled through the scene.
Now we’re ready to start looking for explosive residue: the traces left behind the explosive chemical reaction that has just taken place. There are three main areas we’ll be visiting on this residue hunt. They are the device itself (or its remnants); the origin of the blast; and any surrounding surfaces.
The heat of the moment: blast origin
With that in mind then, have a look at the origin of the blast first, as this may provide clues for where else to look for residues. The origin of the blast is frequently referred to as the “seat of the explosion” and depending on the device and its placement, may or may not have left a crater. Irrespective of whether a crater is present or not, the seat of the blast will certainly contain explosive residue and therefore we start our hunt here. Bits of the device itself may be present and also lend them selves to analysis. We take samples of soil, debris and the device from the crater and seal it in airtight containers, to prevent elements escaping in gas form. These will be analysed later.
Knuts and bolts: device components
Our second area of focus will be any components of the device that have been found. Examining the device is crucial as it will tell you what type of bomb caused the explosion in the first place, which provides valuable clues for investigators. The police and bomb squad will be wondering who had access to materials to build the type device present. So finding out what the bomb consisted of is vital. There are a vast amount of bombs ranging from the chemical to the mechanical and a similarly a wide array of detonators exist from electrical remote to physical buttons or switches. Any bits of the device discovered will have explosive residue all over it. Larger parts of the device can be seized and retained in the same air tight containers mentioned above.
Here, there and everywhere: surrounding surfaces
Finally, we need to look at the surrounding surfaces. Imagine standing in the middle of a room in your house, holding a balloon filled with very finely ground pink chalk. Now clap your hands around the balloon with ferocity. When you’ve realised that you’ve ruined all your furniture, you’ll see that everything in the vicinity is covered with a fine pink chalk residue. If we apply this principle to a bomb, we can see that every surface exposed to it (this may include people present at the time of the blast) will have the balloon’s (or bomb’s) fingerprints all over it, in the form of explosive residue. Bear in mind that the force of the blast may have caused these surfaces to become scattered over a wide area. Bits of residue may be found on roofs or in gutters. Again, these can be swabbed, or depending on the object, seized.
In reality, this is precisely the type of investigation that’s best left to bomb analyst experts; in fact, most local police stations don’t hire investigators familiar with explosive residue handling or analysis. Larger law enforcement organisations, like the FBI, are more likely to have the right specialists in-house.
Your Turn: Is there any other step involved in looking at explosive residues at the scene in question? Have you ever worked out in the field after an event like the one we’ve described? Let us know in the comments. We’d like to hear from you.