NOISE
Two basic audible effects are produced by explosive and pyro- technic devices: a loud explosive noise (called a "report" or "salute" in the fireworks industry) and a whistling sound.
"salute" in the fireworks industry) and a whistling sound. A report is produced by igniting an explosive mixture, usually under confinement in a heavy-walled cardboard tube. Potassium chlorate and potassium perchlorate are the most commonly used oxidizers for report composi s , which are also referred to as "flash and sound" mixtures. hese mixtures produce a flash of light and a loud "bang" upon ignition. Black powder under sub- stantial confinement also produces a report.
"Flash and sound" compositions are true explosives, and they will detonate if a sufficient quantity of powder (perhaps 100 grams or more) is present in bulk form, even if unconfined! Chlorate-based mixtures are considerably more hazardous than perchlorate compositions because of their substantially lower ig- nition temperatures. However, flash and sound compositions made with either oxidizer must be considered very dangerous. They have killed many people at fireworks manufacturing plants in the United States and abroad. Mixing should only be done using remote means, and the smallest feasible amount of com- position should be prepared at one time. Bulk flash and sound powder must never be stored anywhere near operating person- nel.
The famous Chinese firecracker uses a mixture of potassium chlorate, sulfur, and aluminum. The chlorate combined with sul- fur makes this mixture doubly dangerous for the manufacturer. The ignition temperature of the potassium chlorate/sulfur system is less than 200°C! The presence of aluminum - an excellent fuel - guarantees that the pyrotechnic reaction will rapidly prop- agate once it begins. Safety data from China is unavailable, but one has to wonder how many accidents occur annually from the preparation of this firecracker composition. The preparation of potassium chlorate/sulfur compositions was banned in Great Britain in 1894 because of the numerous accidents associated with this mix- ture!
The standard American flash and sound composition is a blend of potassium perchlorate, sulfur or antimony sulfide, and alu- minum. The ignition temperature of this formulation is several hundred degrees higher than chlorate-based mixtures, but these are still very dangerous compositions because of their extreme sensitivity to spark and flame. Ignition of a small portion of a "flash and sound" mixture will rapidly propagate through the en- tire sample. These mixtures should only be prepared remotely, by experienced personnel. The table lists several "flash and sound" formulas.
Flash and Sound Compositions