An explosive is a substance, an element, a compound, or a mixture, which is capable of exerting pressure on its surroundings on explosion / transformation.
Role of Forensic Science in Explosives Examination
Forensic Science plays a role concerning explosives. Explosives studied by forensic personnel mainly relate to mass destruction episodes wherein bombs are used for illicit activities. The explosive residues collected from the crime scene are examined for such causes especially the constitution of the explosive material, the source, and intention of the explosion.
Applications of Explosives
An explosive has many applications, which are legal and do not cause harm to any human, animal, or another living being.
- Legitimate Uses
An explosive might be used in blasting rocks for mining, oil explorations, satellite and spacecraft propulsions, in constructing roads, railway lines, etc, in firework displays, and may also be used for military purposes.
- Illegitimate Uses
The criminals are using explosives for destroying individuals or a nation by blasting bombs. The illegitimate use of explosives causes large-scale destruction, as well as a threat to the integrity of any nation, and is severely punishable under the Indian Penal Code, Explosive Act, and The Explosives Substance Act. Some common examples of explosives are RDX, TNT, TETN, ANFO, Dynamite, etc.
Explosives can be detected before explosions (during trafficking) and also after the explosion by forensic spot tests and also by hi-tech forensic analytical tools.
In simplest terms, we can define an explosion as a rapid increase in the volume of gaseous substances and release of energy along with the generation of high temperature and release of gases.
Also Read: QnA on Explosives
Classification of Explosives
The Explosives can be classified based on composition, velocity, sensitivity, and physical forms. But broadly explosives are of three types: Low explosives, high explosives, and miscellaneous. The latter is sub-divided into homemade explosives, nuclear explosives.
Low explosives are solid flammable materials that deflagrate. Low explosives liberate an enormous quantity of gases that generate sufficient pressure to force a projectile in a specific direction upon ignition and decomposition. The proportion of burning of explosives depends on combustion gas pressure, grain size, form, and composition.
Low explosives experience deflagration at amounts that fluctuate from a few centimeters per second to about 400 meters per second. Gunpowder or black powder, smokeless powder, flash powder, Pyrotechnics are a few common examples of low explosives.
Gunpowder was the first chemical explosive. Gunpowder is an admixture of sulfur, charcoal, and potassium nitrate. The sulfur and charcoal act as fuels, while the potassium nitrate works as an oxidizer. Gunpowder has been extensively used as a propellant in firearms and as a pyrotechnic composition in fireworks owing to the extent of heat and gas volume that it produces.
Pyrotechnics is a methodical technique involving the use of constituents skilled at undertaking self-contained and self-sustained exothermic chemical reactions for the generation of heat, light, gas, smoke, and/or sound. Pyrotechnics has the propensity to change fire into either a burst of striking fireworks or a dense cloud of clogging smoke. The fireworks are a blinking, fiery, short-lived burst of glowing, colored aerial lights.
The explosives detonate, meaning that the explosive shock front passes through the material at a supersonic speed. These are commonly used in carrying out activities involving mining, destruction, and military applications. The high explosives may be further grouped into primary and secondary high explosives. High explosives experience detonation with an explosive velocity ranging from 3 to 9 km/s. RDX, PETN, TNT, ANFO are examples of high explosives.
Primary High Explosives
The explosives which are extremely sensitive to mechanical shock, friction, and heat, to which they will respond by burning rapidly or detonating are known as primary high explosives. Lead Azide, lead styphnate, DDNP, and tetrazene are some of the examples of primary high explosives.
Mercury fulminate is prepared by dissolving mercury in nitric acid and then pouring it into ethanol. A vigorous reaction takes place, which is accompanied by the evolution of white fumes, followed by brownish-red fumes, and finally again by white fumes. Crystals of mercury fulminate are formed at the same time. The grayish-colored crystals are recovered and washed with water until all of the acids are removed.
A lead Azide is a form of primary explosive. It’s made by dissolving lead nitrate in a dextrin-based solution and adjusting the pH to 5 with one or two drops of sodium hydroxide. This solution is heated to 60-65 degrees Celsius and stirred. The sodium azide solution is then added dropwise to the lead nitrate solution, dissolved in a sodium hydroxide solution. The mixture is then left to cool to room temperature with continuous stirring. Lead azide crystals are filtered, washed with water, and dried.
They are also known as base explosives. They are comparatively unresponsive to shock, resistance, and heat. They may ignite when exposed to heat or flame in trivial, liberated quantities. To increase the power of blasting caps, they are sometimes added in small amounts. The secondary high explosives may be further divided into boosters and main charges.
Secondary High Explosives- Boosters
An explosive booster serves as a link between a low-energy and a low-sensitivity explosive like TNT. It increases the explosive shockwave from an initiating explosive to the point where the second charge is detonated. PETN and RDX are categorized as Boosters.
PETN (Pentaerythritol tetranitrate)
PETN is prepared by nitrating pentaerythritol, which in turn is made by mixing formaldehyde with calcium hydroxide in an aqueous solution held at 65-70 degrees Celsius. Nitration of pentaerythritol is achieved by adding it to concentrated nitric acid at 25-30 degrees Celsius to form PETN. The crude PETN is then removed by filtration, washed with water and then neutralized with sodium carbonate solution, and finally recrystallized from acetone. This results in a 95% yield of PETN.
RDX (Cyclotrimethylenetrinitramine, 1,3,5-Trinitroperhydro-1,3,5- triazine)
RDX is synthesized by adding hexamethylenetetramine to excess concentrated nitric acid at 25 degrees Celsius and warming it to 55 degrees Celsius. RDX is precipitated with cold water and the mixture is then boiled to remove any soluble impurities. Finally, purification of RDX is carried out by recrystallization from acetone.
TNT is also produced by the C-nitration process. It is formed by the nitration of toluene with a mixture of nitric and sulphuric acids. Toluene is first nitrated to mono-nitrotoluene and then to di-nitrotoluene and finally, it gets converted to crude tri-nitrotoluene.
The Bachman method produces HMX as a by-product during the production of RDX. Hexamethylenetetramine, acetic acid, acetic anhydride, ammonium nitrate, and nitric acid are mixed and heated at 45 degrees Celsius for 10 minutes. Ammonium nitrate, nitric acid, and acetic anhydride are then slowly added and left on a steam bath for 12 hours. A precipitate form that contains 27% RDX and 73% HMX.
HNS (Hexanitrostilbene)/ 1,1′-(1,2-ethenediyl) bis [2,4,6- trinitrobenzene]
HNS stands for hexanitrostilbene and can be prepared by many methods. For example:
- By the reaction of nitro derivatives of toluene with benzaldehyde, by the reaction of nitro derivatives of benzyl halides with alkaline agents.
- By removing hydrogen chalcogenide
- By the oxidation of nitro derivatives of toluene
Ammonium Nitrate is formed by injecting gaseous ammonia into 40-60% nitric acid at 150 degrees Celsius. By spraying droplets of molten ammonium nitrate solution, dense ammonium nitrate crystals are formed. The spray produces spherical particles known as ‘prills’. These crystals are non-absorbent and used in conjunction with nitroglycerine.
Another explosive formed by the C-nitration process is TATB. It is produced by the nitration of 1,3,5-trichloro-2,4,6-trinitrobenzene, where, 1,3,5-trichloro-2,4,6-trinitrobenzene is prepared by the nitration of tri-chlorobenzene with a mixture of nitric acid and sulfuric acid. 1,3,5-trichloro-2,4,6-trinitrobenzene is then converted to 1,3,5-trinitro-2,4,6- triaminobenzene (TATB) by nitrating with ammonia. The yellow-brown crystals of TATB are filtered and washed with water.
Dynamite is divided into gelatine and non-gelatine classification. Gelatine dynamite is made by dissolving nitrocellulose in nitroglycerine and forming a gel at 45-50 degrees Celsius. By using large vertical mixer blades, the mixture is stirred. The other components are added once the gel has been produced. After that, the explosives combination is extruded or pressed into long rods, which are then cut into smaller pieces and packaged in paraffin-coated paper cartridges.
Non-gelatine dynamite is made in the same way as gelatine dynamite but without the use of nitrocellulose in the formulations.
Gelatine dynamites are basically of four types:
- Gelatine dynamite
- Semi gelatine dynamite
- Ammonia gelignite
It includes the:
- Molotov Cocktail
- Improvised Explosive Device
A Molotov cocktail is made up of a glass bottle half-filled with flammable liquid, commonly gasoline (petrol) or alcohol (methanol or ethanol); the mouth of the bottle is sealed with a cork or other airtight stopper (rubber, glass, or plastic); and a cloth rag is wrapped tightly around the mouth. The weapon is activated by soaking the rag in a flammable liquid right before use, lighting it, and then throwing the bottle at the target. On impact, the bottle shatters, spraying flammable liquid all over the target, which is then ignited by the burning rag.
An improvised explosive device (IED) is a product, assembled in contravention to the existing rules of law of the nation adopting unconventional or semi-conventional methods of formulating ammunition/explosives, with a criminal/anti-national intention. IED is also known as a homemade bomb. For example- roadside bombs, letter bombs, bombs incorporated in briefcases/vehicles, etc
Components of an IED
IEDs are formed by incorporating destructive, lethal, and noxious, pyrotechnics or incendiary chemicals. An IED is composed of explosives, a detonator, a power source (battery), and an Initiation mechanism (switch).
While looking for an IED, keep the following do’s and don’ts in mind:
1. Don’t touch or handle suspicious objects
2. Don’t believe that only one device has been planted.
3. For all locations up to 250 sq. ft., use a maximum of two people per room.
4. Mark the area to be searched
5. Trust nothing and assume nothing to be safe
6. Obtain maximum information about the device
7. Before entering a room, pay careful attention to any strange voices or sounds.
8. Be careful with any hidden dangers, both at the entry during the search.
9. Take a visual survey of the entire room.
10. Search the area from front to back.
11. Make a report about the area and the suspected material as soon as possible.
12. Ask for help from expert
A letter bomb is an explosive device that is sent through the mail and is intended to injure or kill the recipient when it is opened. They are also used in terrorist attacks. They are usually designed to explode immediately on opening, to seriously injure or kill the recipient.
A booby trap is a device, which is made to startle, surprise, attack, or kill an individual. A booby trap is generally triggered accidentally by the presence or movements of the victim. Booby Trap often has some form of enticing to attract the victim towards it. The booby trap is sometimes placed on busy roadways or activated when the victim acts such as opening a door, picking up something, turning something on or off, and so on.
It is generally known as a radiological dispersion device (RDD). A dirty bomb is a radiological weapon. It is a combination of radioactive material with conventional explosives such as dynamite. A dirty bomb is used to contaminate the affected area with radioactive material. The primary goal of a dirty bomb is to threaten people. People may also be exposed to radioactive substances.
Characteristics of Explosives
The following are some of the important characteristics of an explosive which are very important to determine whether the explosive is suitable for a particular use:
- Availability and cost
- Sensitivity to initiation
- Velocity of detonation
- Power, performance, and strength
- Explosive train
- Oxygen balance
- Chemical composition
- Chemically pure compounds
- A mixture of oxidizer and fuel
Various physical effects are depending on the type of explosion whether it is mechanical, chemical, nuclear, or electrical. The severity of the effect depends on several factors, such as type of explosion, amount of energy or fuel present, weather conditions, and others. The chemical reaction goes on when an explosive material explodes/detonates.
It creates four types of effects as Blast Pressure, Thermal, Fragmentation, and Ancillary.
Blast Pressure-Positive and Negative
Positive Blast Pressure
Positive blast pressure is the first effect that follows an explosion/detonation of an explosive. The expanding product gases push on the surrounding air when an explosive charge explodes or a containment vessel fails following a deflagrating low explosive in a pipe bomb. It produces and forces out a shock wave.
Negative Blast Pressure
After the energy generated in the positive-pressure phase of an explosion expands, the longer-lasting, lower velocity negative blast pressure phase begins.
Fragmentation is missiles. The results from an explosion may be a part of the explosive casing, container, earth, building material, target area, or other items affected by the explosion. It may be subassemblies or fragments or fragments of apparatus or constructions or complete items. An exploding explosive or bomb does not affect the fragmentation effect of an explosion. Fragmentation can and does result from accidental explosions of other materials such as gas, dust, and mechanical assemblies.
The incendiary or thermal effect is the heat produced from the explosion or decomposition of an energetic material. The temperatures from this reaction and burning process, depending on the explosive, can reach or even exceed 70000 F. This is very fast and there is a short release of heat.
Effect on Living Things
People close to or in the vicinity of blast incidents are prone to get affected. Usually, the following individuals are used to get more affected:
1) People wearing little or no protection
2) Bomb Disposal Technicians
3) Soldiers wearing body armor or deminers.
Overpressure is the abrupt and extreme upsurge in ambient pressure which can harm the internal tissues, probably leading to everlasting harm or death.
Fragmentation includes shrapnel. It also includes debris, soil, and vegetation from the site covering the blast source which is very common in anti-personnel mine blasts.
When the overpressure wave collides with the body it can cause low levels of blast-induced acceleration. Resultant injuries array from insignificant to unsurvivable.
Finally, wounds and casualties can result from the explosive fireball as well as inflammable means projected onto the form. Personal protective instruments, like a bomb suit or helmets, collaborative, visors, and foot protection, can effectively diminish the special effects, depending upon the charge, proximity, and other variables.