GUNPOWDER & EXPLOSIVES
Overview
In the investigation of crimes involving the use of firearms, law enforcement
officers need to know whether a suspect has fired a gun or not and the gunshot range
or the approx. the distance of the shooter to the victim. When a firearm is discharged
unburned particles of the gunpowder may escape thru the breech of the gun and
deposit on the hands of the shooter, on the clothing of the victim and some may
remain in the barrel. These gunpowder residues can be detected by chemical
examination.
In connection with suspected bombings, the lab is requested to detect traces of
explosives that may be found in the remains of parts of a bomb. Explosives like
improvised and manufactured dynamite used in illegal fishing, are also examined.
Learning Objectives
At the end of the unit I am able to:
1. Define relevant terms.
2. Identify the chemical and physical properties of gun powder and explosives.
Lesson Proper
In the investigation of crimes involving the use of firearms, the three most
important problems may arise:
1. Determination of whether or not a person has fired a gun with his bare hands
within a pertinent period of time.
2. Determination of the probable gunshot range, which is the distance the firearm
was held from the body of the victim at the time of discharge.
3. Determination of the approximate time of firing of the gun or the approximate
date of last discharge.
Two Kinds of Gunpowder
1. Blackpowder – It is consists of an intimate mixture of charcoal (Carbon -15%),
(Sulfur – 10%), and (KNO3 or NaNO3 – 75%).
2KNO3 + 3C + S → 3CO2 + K2S + N2
2. Smokeless powder - It is consists of cellulose nitrate or glyceryl nitrate combined
with cellulose nitrate and some stabilizers. When exploded the following reactions
occur:
C12H14O4(NO3)6 → 9CO + 3N2 +7H2O + 3CO2
cellulose nitrate
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4C3H5(NO3) 3 → 12CO2 +10H2O + 6N2 + O2
glyceryl nitrate
Possible locations of gunpowder residue
1. Residue of the barrel of the gun.
2. In or around the wound.
3. On the clothing of the person fired upon at close range.
4. On the exposed surface of the hand of the person firing the gun.
Factors that affect the presence and amount of gunpowder residues
1. Type and caliber of the ammunition.
2. Length of the barrel of the gun.
3. The distance of the muzzle of the gun from the target
4. Humidity
5. Wind velocity and direction.
6. The direction of the firing.
Paraffin test (Dermal Nitrate test or Diphenylamine test or Lunge’s test) – a test to
determine whether a person fired a gun or not with his bare hands. The basis of this
test is the presence of nitrates in the gunpowder residue. Warm melted-paraffin wax
applied on the hands of the shooter will cause the pores of the skin to open and exude
the particles of the gunpowder residue. These particles are collected by the paraffin
cast and will appear as blue specks when the diphenylamine reagent is added to the
cast. The specks are generally located in the area of the thumb and forefingers.
Positive Result – Deep blue specks develop when nitrates come in contact with
diphenylamine reagent.
Note: The result of this test is not conclusive because it does not always show that
nitrates or nitrites were necessary results of the discharge of firearms. Other
substances yield the same positive reaction for nitrates or nitrites, such as explosives,
fireworks, pharmaceuticals, and leguminous plants such as peas, beans, and alfalfa.
(People v. Baconguis, 417 SCRA 66, December 2, 2003).
Factors to be Considered in the Interpretation of Paraffin Test Result:
1. Time of reaction
2. Number of specks
3. Location of specks
4. Character of specks
Other Sources of Nitrates:
1. Fertilizers
2. Urine
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3. Explosives
4. Cosmetics
5. Tobacco
6. Detergents
7. Firecrackers
Possibilities That a Person Maybe Found Negative Even If He Actually Fired a Gun:
1. Use of automatic pistol
2. Direction of wind
3. Wind velocity
4. Excessive perspiration
5. Use of gloves
6. Knowledge of chemicals that will remove the nitrates
Determination of the Probable Gunshot Range:
The clothing of the victim with bullet perforations should be submitted for possible
gunshot range. It is only possible to determine the probable gunshot range if the gun
was fired from a distance of zero (contact firing) to 36 inches (3 feet) based on the
distribution of powder patterns or the spread of a shot pattern.
Three Zones of Distance
1. Those in which the muzzle of the gun was held directly in contact with the body
or practically so. (contact wounds).
Contact wounds – Damage (on cloth) is due more to the flame and the muzzle blast
than to the penetration of the bullet. Describe by the following;
a. The gaping hole where fabric is badly torn,
b. The blackened area surrounding the bullet hole,
c. Singeing of the fibers at the entrance, and
d. Presence of partially burned powder residues around the entrance hole.
2. Those in which the muzzle of the gun was held from about 2 inches to 36 inches
away.
Distance from which the firearm was discharged Characteristic Pattern
4. Those in which the muzzle of the gun was held from 36 inches or more
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Distance from which the Characteristic Pattern
firearm was discharge
0 to 2 inches Gaping hole, smudging, singeing, tattooing and
burning. Smoke & soot is deposited around the hole of
entrance producing a dirty, grimy appearance.
Individual specks of tattooing around the hole are
visible with the naked eye.
2 inches to 8 inches Smudging
8 inches to 36 inches Partially burned and unburned powder particles are
driven into the surface around the gunshot hole
producing a black coarsely peppered pattern called
tattooing.
Beyond 36 inches Evidence of powder tattooing is seldom present.
Nitrate particles may be present.
Determination of the Probable Time The Gun Has Been Fired
1.Rust: Formation of rust inside the barrel after a gun has been fired is a good
indication for the determination of the approximate time the gun has been fired.
a. If a gun has not been fired at all, no rust can be detected inside the barrel of the gun.
b. If a gun has been fired, iron salts are formed and are found inside the barrel. These
iron salts are soon oxidized resulting in the formation of rust.
2. Presence of nitrite (NO2) – firearms could have been fired recently. Gives blue color
in paraffin test results.
3. Presence of nitrate (NO3) – firearms could have been fired but not recently. Gives
a yellow-green color in paraffin test results.
Types of Explosives
1. Mechanical – such as those caused by the expansion of gas-producing high pressure
beyond the capacity of the container.
2. Atomic – resulting from atomic transformations.
3. Chemical – produced thru the extremely rapid transformations of the unstable
substances accompanied by the formation of heat.
Classification of Explosives
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The speed of the chemical reaction or detonation of the explosives determines
the classification of explosives as low, initiating, or high explosives.
1. Low explosives are low burning and are used mainly as propellants, like black
powder and smokeless powder. Atomic explosive results from atomic
transformations.
2. Primary or initiating explosives are extremely sensitive to detonation by heat,
shock friction, and impact. They detonate without burning, like lead oxide and
mercury fulminate.
3. High explosives detonate under the influence of shock of the explosion of a primary
explosive. Examples are the following:
a. Ammonium nitrate – the cheapest and most readily available salt of nitric acid.
b. TNT (trinitrotoluene) – the most widely used explosive.
c. Nitroglycerine – most widely used commercial explosive.
d. RDX – considered one of the most important military explosives used today.
e. C4 – a plastic explosive that is white and dough-like in texture.
f. Chloroacetophenone – CN is the principal component in the filler used in tear gas
solutions.
4. Fire Bombs – Molotov cocktail which is an incendiary device, acids mixed with
gasoline, alcohol, and gasoline, etc.
References
Melcon S. Lapina, MSCrim, Forensic Chemistry, and Toxicology, [Powerpoint slides]
Aries Gallandez, Forensic Chemistry, International School of Asia and the Pacific,
[Document ]
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