Jeya Rajendran and T. L.Thanulingam
Abstract: The noise levels from sound-producing firecrackers, both commercial and newly formulated, were measured. Commercial sound-producing firecrackers produce noise in the range of 130.7 dB(AI)/150.4 dB(C) peak to 142.8 dB(AI)/162.6 dB(C) peak at a distance of 4 m. A set of pyrotechnic compositions of potassium nitrate (KNO3), sulphur (S), aluminium (Al) and boric acid (H3BO3) was used to produce different varieties of sound-producing firecrackers for analysis. A bulk density of 0.44-0.50 g cm-3 was maintained for homogeneity of the mixture. The factors influencing the sound from firecrackers, such as amount of mixture, weight percentage of oxidizer and fuel, particle size of the ingredients, bursting strength of the paper used for the inner paper case of the firecracker unit and variation in percentage composition, were studied. The noise level produced from different sizes of firecracker units shows a linear relationship with the weight of the mixture used and the bursting strength of the paper. It was found that the pyrotechnic mixture of composition 57.5/20/22/0.5% KNO3/S/Al/H3BO3 in a firecracker unit made from 240 gsm kraft paper and bursting strength 2.2 kg cm-2 produced allowed sound levels of <125 dB(AI)/145 dB(C) peak at 4 m distance. The efficiency of the pyrotechnic mixture for making fireworks is explained by measuring the safety characteristic data of thermal and mechanical sensitivity. Furthermore, a comparison between a mixture containing potassium chlorate, i.e. KClO4/S/Al(H3BO3), and KNO3/S/Al(H3BO3) was made on the basis of sensitivity measurements. The limiting impact energy (LIE) of pyrotechnic flash compositions of KNO3/S/Al/H3BO3 falls in the range of 5.3 J making the mixtures class III explosives. The ignition temperature was found using differential scanning calorimetric (DSC) analysis to be in the region of 437.9-498 °C. Self-propagating decomposition occurred only at high temperatures for KNO3/S/Al(H3BO3) making the mixture thermally stable.
Keywords: Sound level, noise level, pyrotechnic mixture, impact sensitivity, friction sensitivity, flash composition, firecrackers.
Ref: JPyro, Issue 27, 2008, pp60-76
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