Spark discharge sensitivity

Another type of testing, that of electrostatic sensitivity, has been demonstrated in some cases to be more properly a delicate test of the ignitability of the material under localized thermal stress which correlates best to the friction sensitivity of the system under test rather than to electrostatic hazards. On the other hand, electrostatic tests done in the supposed atmosphere above a propellant mixer were reduced in absolute value by more than an order of magnitude when the ammonium perchlorate dust actually present was introduced in the test since this altered the potential path for spark discharge within the system. 

For a fixed distance, sparking occurs at a critical voltage leading to smoke, flame, flash, crackling, decomposition, ignition or explosion. This critical voltage is a measure of electric spark or electrostatic discharge sensitivity of the explosive under test [71-73]. 

Static Electricity and Sensitivity to Initiation by Electrostatic Discharge. See under Electrostatic Discharges and Sensitivity of Explosives to Initiation by Them in Vol 5, E38-L to E55-L Addnl Refs 1) M.S. Kirshenbaum, Response of Lead Azide to Spark Discharges Via a New Parallel-Plate Electrostatic Sensitivity Apparatus . PATR 4559 (1973) 2) Ibid, Functional... 

Extensive measurements have been made on lead azide in the U.S.S.R. in recent years, but no description is provided of the lead azide. Sten gach [33] carried out a study on the sensitivity of lead azide to spark discharge in relation to density, size of crystals, interelectrode distance, temperature, and presence of inert impurities. The lead azide was pressed into a chamber containing a spark gap formed by two pointed electrodes. The mean density of the azide was varied from 1.1 to 2.7 g/ml and the interelectrode gap was varied from 0.020 to 0.50 mm (0.0008-0.020 in.). The 50% firing point was used as a measure of sensitivity. 

Another method is to use a small wire in a capillary tube as the counter electrode with a spark discharge. The system does not possess high sensitivity but can reveal local differences in compositions that may be significant in quality control. 

The electric spark sensitivity or electrostatic sensitivity test determines the minimum amount of energy of an electric spark discharge that will cause initiation of the tested sample. 

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