Post Blast Explosive Residue Collection and Analysis

A picture of a blast where a text is written as Post blast residue collection and analysis

The investigation of explosions features a long history in forensic science and covers incidents ranging from accidents within the home or workplace to major terrorist attacks.

However, establishing the nature of an explosion can be a significant challenge to the forensic investigator as fire often follows an explosion. This causes complications for the investigators as maximum valuable evidence is then destroyed.

Explosives may be solid, liquid, or in gaseous form. The most commonly found explosives in the crime scene include the following:

  1. Blasting explosive– Cylindrical form wrapped in waterproof papers and stamped with maker’s name
  2. Gun powder– Black, brown, or grey color available in cylindrical, grain, or powder form.
  3. Guncotton– It has a look of ordinary cotton.
  4. Fulminates– White or grey powders, which are extremely dangerous.
  5. Picric acid and picrates– Yellow crystalline or powder form.
  6. Ammonal – Silvery brown powder.
  7. Chlorate or potash– Crystals or white powder.
  8. Arsenic sulfide– Yellow or orange powder
  9. Detonators and caps- It contain detonating charge in metal tubes or cups.
  10. Crude bombs and IEDs– Explosives contained in bottles, jars, coconut shells, pipe coupling, cloth or jute balls, transistors, tiffin carriers, soft drink cans, etc.

Bomb Disposal, Collection, and Handling of Explosives

During the removal, guarding, or handling of explosives, all persons should be kept away. In addition, investigating officers should be careful about the booby traps.

BOOBY TRAPS are bombs which are timed to explode in the presence of a person while he is engaged searching premises for any incriminating objects.

In most cases of an explosion, a bomb disposal squad is summoned. Use detectors like a metal detector, explosive detectors, and x-ray fluoroscopy extensively at all vulnerable points.

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Unexploded bombs may be found in public places such as railway stations, bus stands, airports, industrial installations, cinema houses, etc. Therefore, it is crucial to protect human life and public property.

When a substance is solid or liquid, a few solid grains are taken on paper or tin foil. After removing it at least five meters away from the main bulk, it is tested by

(a) Placing it on a flat surface and then hammering and

(b) Burning a small portion over a small flame.

  • In liquid, 10 to 15 ml is placed in a small clean bottle corked up, and after packing in cotton wool in a box or tin, it should be sent to the concerned controller of explosives. 
  • In the case of solid, a few grains are placed in a clean small bottle, filled with clear water, and then packed and sent for examination. If any change is found with water, a perfectly dry and clean bottle should be used and packed, and sent in the same manner. 

When the object is ablating explosive, detonators, cap, fuse, cartridge, firework, etc., they should not be sent through post under any circumstances. Instead, a few samples should be separately packed in cotton wool, placed in a wooden box, and sent through a messenger to controller explosives with the report.

  • Bombs can be found in military grenades, soda water bottles, tiffin carriers, jam tin, coconut shells, etc. It should not be touched or moved. It is always safe to send information to the controller of explosives or bomb squad for assistance.
  • In cases of bombs made of soda bottles, it is placed as it is in a string bag, and then with the help of a solid cord, it is lowered into a large bucket containing hot water from a safer distance.
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It is left for around 24 hours without disturbing. It may be then taken out and carefully wrapped in wet straw or cotton wool and then packed in a wooden box. It is then sent for further examination.

  • If phosphorus is found in incendiary devices, it is advised not to touch with hands. It should be transferred to a small bottle containing water, well corked, and then packed and sent.
  • If sulphuric or nitric acid is present, the sample should be separately sent in a glass stoppered bottle, securely sealed.
  • If an orange powder or whitish-yellow powder is found in large quantity, it should be moistened with water, and only a portion of a sample, wetted with water and adequately packed, should be sent for further examination.
  • When a gas cylinder is found, the cylinders should be kept cool and sent for examining and ascertaining their nature.

Examination of Explosive Residue

A police officer moving around in a crime scene where a blast had happened earlier

At the explosion scene, some quantity of explosive, explosive ingredients, or degraded product of explosives would invariably be found on victims of explosion or the debris that lie in and around the place.

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Collection of these materials and systematic chemical analysis in the laboratory help identify the explosives used and help reconstruct the device used in the explosion.

  • Visual examination of the debris is the preliminary step as it can put together the exploded ingredients to identify the explosive devices and locate the traces of chemically unchanged explosives. Microscopic examination will help in detecting traces of unconsumed explosives.
  • Various chemical tests have been developed to detect organic and inorganic traces of explosive debris.
  • Modern instrumental methods are the most preferred methods for isolating and detecting explosive materials from the debris.
  • Solid particles can be examined using infrared spectroscopy (IR) or scanning electron microscopy coupled with an energy dispersive X-ray analyzer(SEM-EDX).
  • Vapor trace analyzer(VTA) is used for detecting volatile organic explosives, such as nitro-glycerine, ethylene glycol dinitrate (EGDN), TNT, RDX, and PETN.

However, because of the high volatility of these compounds, High-performance liquid chromatography (HPLC) coupled with mass spectrometry is used.

New technologies and instrumental techniques have improved detection limits of explosive traces in post-blast residues in the recent past. The application of new technology to detect and identify explosives will help investigators suppress criminal misuse of explosives.

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