TO PREVENT ACCIDENT

Dominion, Volume 28, Issue 252, 22 July 1935, Page 8

TO PREVENT ACCIDENT

Experiments With Special Gelignite

LOW FREEZING EXPLOSIVE

To prevent accidents that result from the careless warming of explosives, the Department of Internal Affairs is conducting experiments in West Coast and Southland mines with a special lowfreezing gelignite and there are some hopes that this special explosive will prove satisfactory for New Zealand conditions, said Mr. J. Girling Butcher, Inspector of Explosives, in the course of an interview. No regulations would be effective to prevent accidents such as that which occurred a week ago when several people were injured as the result of au explosion of gelignite that was being warmed in a kitchen oven. Every packet of gelignite had a notice, plainly printed, warning against the improper use of it and instructing that to thaw frozen explosives a special warming pan with a water jacket was essential. Beyond that, regulations could not go, but the crop of accidents that occurred every year might be avoided by the use of a new kind of gelignite. Gelignite did become frozen under New Zealand conditions, said Mr. Butcher, and there were recognised safe measures for thawing. One was to use a double-lined vessel with a water jacket; another was to store gelignite in manure-pits to secure slow warming well within a safe temperature; aud the method adopted by mining companies was to heat magazines with electric heaters in such a manner that there was no possibility of contact.

The reaction of gelignite to freezing was very peculiar. It all depended upon the crystals of the nitro-glycerine. Sometimes frozen gelignite became very insensitive and would not detonate; at other times freezing so changed the crystals that the nitro-glycerine became extremely sensitive. It was thought that formation of needle-shaped crystals caused extreme sensitivity under freezing conditions. It was known for a fact that gelignite sometimes needed no percussion or heat to explode it. One piece of frozen gelignite was tossed over a tip. It exploded in the air merely as the result of the movement! “The department is now experimenting with low-freezing gelignite which is made with a modification of the ordinary nitro-glycerine freezing at a much lower temperature," said Mr. Butcher. “This will not require thawing under New Zealand conditions. Samples are under test in the Ohai group mines in Southland and on the West Coast. It will be stored in unheated buildings through the winter, and samples will be tested from time t<s time to determine its effectiveness. “It is possible the whole of the mining explosives will be changed over to this type if the tests are satisfactory and the necessary arrangements can be made for satisfactory supply. There is some difficulty owing to the fact that ethylene glycol, from which this explosive is made, is not manufactured in Australia.

“Gelignite usually is made with nitoglycerine jellied with nitro-cotton —a modification of guncotton. The jelly is mixed in with a dope of nitrate of potash and wood meal. At about 200 degrees Centigrade nitro-glycerine decomposes. Under those conditions it must explode. It is usual for two or three fatalities to occur every year through heating explosives carelessly, in spite of every precaution and warning. The experiments are designed to avoid that.”