Particle classification scheme

Two other similar cases were subsequently experienced and as a consequence it was decided to act on the side of safety by reclassifying barium, calcium, silicon particles as indicative, rather than unique, to the discharge of a firearm. 

Particle Type Number Approximate % Number Approximate % 

Discharge residue particles from starter pistol blanks were examined for comparison with discharge residue particles originating from firearms ammunition. Table 19.1 gives the starting pistol discharge residue particles classified according to their consistency with FDR particles. 

The particles detected were all in the size range 1 to 19 pm. Both spherical and irregular particles were found and all had the appearance of having partially or wholly condensed from a vapor or melt, and all exhibited some degree of curvature. They did not exhibit any degree of crystallinity and their surface details were smooth, irregular, cratered, or nodular. The physical characteristics of the particles were indistinguishable from FDR particles. 

Individually, the starting pistol discharge residue particles could not be distinguished from FDR particles, by physical appearance, by size range, or by elemental composition, which includes the additional accompanying elements. ft is a reasonable assumption that discharge residue particles from 

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The particle classification scheme is the basis of the particle analysis method for FDR detection and identification. A revised particle classification scheme is presented in a later chapter. 

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). 

The validity of the particle classification scheme was tested by examining items that may produce similar particles, paying particular attention to blank cartridges, the main uses of which that are likely to be encountered in casework are cartridge tools and blank firing replica/imitation firearms. 

The particle classification scheme is based on modern primed ammunition and consequently mercury fulminate-primed ammunition is not included. Mercury-containing particles from the discharge of mercury fulminate-primed ammunition are rarely detected in casework. Discharge residue from such ammunition was tested in an effort to provide an explanation for this. Discharge particles from Sintox-primed ammunition was also examined with a view to anticipating future problems the criminal use of... 

To clarify the list of accompanying elements in the particle classification scheme and the levels at which they are found. 

From casework statistics the unique particles (those containing the combination lead, antimony and barium, and those containing antimony and barium) occur in the ratio 7 3, respectively. Approximate percentages for indicative particles are lead-only 55% lead, antimony 20% lead, barium 8% antimony-only 7% barium, calcium, silicon 5% barium-only 5%. Table 19.3 gives an indication of the levels of the primary elements in each particle type. Table 19.4 gives an indication of the levels of accompanying elements in each particle type and is the basis for note b in Table 19.5, Particle Classification Scheme. 

The original particle classification scheme192 has been revised based on casework experience, research work on blank cartridges, and so forth, and a detailed analysis of 14 years of casework results. The particle classification scheme used in Northern Ireland since 1984 is given in Table 19.5. The indicative particles are in tentative order of decreasing significance. 

The particle classification scheme, developed as described in reference 200, did not include mercury fulminate-primed ammunition, which is frequently encountered in Northern Ireland, and is currently manufactured in some Eastern Bloc countries. 

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