Primer discharge

Table 22.9 Mercury Levels from Primer Discharge...

P. Bergman, E. Springer, and N. Levin, Hand Grenades and Primer Discharge Residues, Journal of Forensic Sciences (JFSCA) 36, no. 4 (1991) 1044-52. 

A. F. Schlack, "Susceptibihty of Electric Primers and Electrostatic Discharges" ia Minutes of the 15th Explosives Safety Seminar, AD-775 580, NTIS, Spriugfield, Va., 1973. 

Molecules such as TATP (49) possess explosive strength similar to TNT. Furthermore, TATP is extremely sensitive to heat and vibrational shock and can be ignited with an open flame or small electrical discharge i.e. does not need a primer unlike conventional explosives. 

A study of static charge build-up on the human body in an arctic environment and how it might affect initiation of primers was reported recently (Ref 57). For an earlier discussion of charge build-up on humans see Ref 33. Operations are considered hazardous when the electrostatic energy potential during the suspected operation exceeds the threshold initiation level for the hazardous material. The human body can constitute a hazard when the material can be initiated by a discharge of less than 0.015 J, as is the case with primary expls... 

Several techniques have been utilized for the detection of firearms discharge residue on the hands of an individual who has recently handled or discharged a weapon. Testing for the presence of nitrates proved unreliable and was discarded. Colorimetric tests for barium and antimony from primer composition were found to lack sufficient sensitivity for general application. 

The development of neutron activation analysis (NAA) as a sensitive and specific method of trace elemental analysis led to its application during the 1950 s for the detection of firearm discharge residue. Its ability to detect and identify very low concentrations of barium and antimony, elements associated with most primer compositions, was encouraging. 

Numerous terrorist activities as well as many serious criminal offensives involve firearms. When a firearm is discharged, a variety of materials is emitted by the muzzle (accompanying the projectile), including primer and gunpowder (propellant) residues... 

In conventional ammunition lead, antimony, and barium are emitted when the ammunition is discharged. These three elements are undesirable from a health viewpoint and pose a major problem for firearms instructors in indoor firing ranges, as they are exposed to an unhealthy environment each working day. To solve this problem Dynamit Nobel AG developed a nontoxic primer composition called Sintox. Lead styphnate is replaced by 2-diazo-4,6-dinitrophenol (diazole) and the barium nitrate and antimony sulfide are replaced by a mixture of zinc peroxide and titanium metal powder. 

Organic constituents could originate from the primer mixture, the propellant, sealers/lacquers/lubricants from the ammunition, and also from lubricants and organic debris already present inside the firearm before discharge. The main source of organic discharge residue is the propellant. 

Particles due to the discharge of a firearm can be loosely divided into two types those originating from the bullet, and those originating from the primer. This is a broad general classification only and is not absolute. Particles classified as primer particles because of their elemental content are... 

Discharge particles can be broadly classified into bullet particles and primer particles. This is not unexpected considering that while vapors are miscible, most inorganic compounds in the liquid and solid state cannot dissolve metals, and vice versa. Upon solidification the metals would be expected to separate from the compounds and form separate particles. 

Experiments were conducted involving the addition of tracer compounds to the propellant, followed by an examination of the discharge particles to determine if any of the particles and which type contained the tracer.173 The tracer was found in primer particles only, which supports the proposition that they should be found dissolved in the oxides and salts originating from the primer and not in the bullet particles. A similar experiment involving the coating of bullets with metals not normally associated with firearms ammunition, followed by examination of the discharge particles, supported the proposition that the bullet material makes a contribution to the primer particles. 

At the start of 1978 the particle analysis method183 replaced the flameless atomic absorption bulk elemental method184 as the firearm residue detection method in the NIFSL. Since then the particle analysis method has been substantially improved by the use of a sample concentration/cleanup procedure,185 the addition of a backscattered electron detector, and the development of an automated residue detection system.186 187 Despite these improvements the technique remains costly and labor intensive. Certain aspects of the system required further work, in particular, the particle classification scheme discharge particles from mercury fulminate-primed ammunition and discharge particles from new primer types (Sintox). 

As antimony sulfide is widely used in primer compositions, sulfur is frequently present in discharge residue particles and can occur at major, minor, or trace level (see Table 19.5). Consequently the occurrence of sulfur at major level is not an accurate indicator of the use of black powder. The particles should be considered as a group and it is clear that the frequent occurrence of both potassium and sulfur at high level is strongly indicative of black powder. However, as can be seen from Table 20.9 the use of black powder does not necessarily yield overall high levels of potassium. Potassium does not normally occur at major level in FDR particles (see Table 19.5) and its presence at major level in any of the particles suggests the use of black powder. 

The residue on the surface of a discharged bullet appears to originate from the base of the bullet itself, from the primer, and from inorganic additives to the propellant. Firings numbered 8,21,34, and 35 had lead-free primers yet lead was detected on the perimeter of the bullet holes. Ammunition with barium-free primers gave barium on the perimeter. 

To clarify the situation it was decided to investigate the possibility that the antimony originated from the bullet. Discharge residue particles originating from ammunition with antimony-free primers and antimony-hardened bullets were examined for the presence of antimony. Results are given in Table 20.14. 

Table 20.14 Discharge Particles from Ammunition with Antimony-Free Primers...

Burned K and S at major level Cartridge case and primer cup Cu with a trace of Zn Discharge primer residue (elements listed in descending order) ... 

There is no lead or barium in the primer yet discharge particles from this ammunition frequently contain lead, antimony, and barium. The lead and barium must come from other components in the ammunition (bullet core/propellant) and/or from contamination in the firearm. Tin was also frequently present in the discharge particles and originates from the tinfoil disc used to seal the primer cup in mercury fulminate primers. 

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