THE ART OF BLASTING

Wanganui Chronicle, Volume 74, Issue 115, 18 May 1931, Page 12

THE ART OF BLASTING

EXPLOSIVES EXPERT WORLD-WIDE WANDERING.! Fur nearly -HI years Mr J. U. Leggo, of ti.e Nobels Ex plosives Company, has been handling explosives in various parts of the world, and he talks ot •‘beautiful shots' with the enthusiasm of an .artist. It happens that his task as a. technical adviser has never found greater scope than in New Zealand. It, is well known that some very large, blasting operations arc carried out in the Dominion, Imt it may not be known, says the New Zealand Herald. that some of the charges used by tlie Wilsons Portland Cement Company in breaking down limestone rock for cement-making are among the largest ever used in the world. The last contained Jsi tons of nitro-glycerine. But the most tricky explosive operations Mr Leggo was ever connected with were the series by which The “dumplings” at the intake and outlet of the Arapuni diversion tunnel were removed. The success of the job proved how valuable a servant of man explosives can when properly handled. A Beach in Peru. In his earlier days Mr Leggo was much in South America, uud many strange tales he can tell of that region. Once, two tons of gelignite was sent to a beach port in Peru where “Life goes by the manana principle.’’ “It was not surprising, therefore,” said Mr Leggo, “that the cases were left two weeks on the burning sand before some one decided that they should be placed in the shade of the scacliff. Four cholos were employed to do the job, but one of them dropped a case, which brought about detonating results. The consequence Nvas that the four cholos were blown to atoms. “The death of four natives did not worry the people concerned, and perhaps nothing more would have been heard about the matter but for the fact that not long afterwards they were loading cattle in the cruel way of the country. The beasts were driven into the water, lassooed, and hoisted on board the ship

“One bullock wandered down The beach to the spot where the gelignite had lain,” continued Mr Leggo. “Apparently part of the oil matter produced from it during the period of decomposition which makes it frightfully sensitive had leaked into the sand. Evidently the grating of the hoofs on the sand fired this unexpected charge and the bullock was blown to bits. Perhaps it was lucky, for any animal that dies young in South America is fortunate. A quarter of the beef landed on the roof of the agent’s place, and he got the wind up badly. He imagined that the beach was liable to do this sort of thing at any time, and 1 was sent to investigate. Of course the one explosion was bound to have cleared up all the explosive, but I made the necessary investigation to convince the agent that no more beef would rain upon him. Pilfered Gelignite “And that was a sad business at Cacabamba. Forty tases of explosive had been packed in from the coast on mules, a distance of 90 leagues, to an altitude of about 15,000 feet. When the stuff got there all the cases were found to contain scones making the exact 1 weight, but packed so nicely that they did not rattle. Fancy pilfering gelignite. “That reminds me of the transport contractor of Mollendo. 1 found that he had built a quadrangle of the cases of explosive and not only had the mules secured within but also his own hut, where his wife had a cooking fire going merrily. When I told him what sort of a fool he was, he explained that as the fire was not. up against the boxes they would be all right.” Mr Leggo had a bright story about Gympie, in Australia. Another explosives man set out to destroy 300 cases that had been condemned on a Satur- , day morning, when all the mine managers were in town. Instead of laying it in trails and setting fire to it against lhe wind, he made a heap and lighted ic. Soon the heat reacned the high temperature necessary to detonate the stuff and there was such au explosion that all the mine managers thought the boilers had burst. “It cost Gympie £12,000 to shift the lo’cal magazine after that,” said Mr Leggo, “and it also cost poor Frazer, who did it, his job. I well remember him coming in with his black moustache and white face, asking me if 1 had seen a boy and a horse and cart. Fortunately, the boy was safe.” Remarkable Powder Accident “Gunpowder is much more dangerous stuff io transport than the high types of explosives, which, with ordinary care, arc harmless. There was a remarkable accident once on the Blue Mountains. Four waggons were going over, the first loaded with barrels of ’ gunpowder. One barrel cracked and the powder trickled in a steady stream into the wheel rut. Apparently the tyre of the second waggon struck a spark on the metal and this trickle of powder acted as a fuse. The flame ran along to the first waggon, leaped up the stream that was falling, and the whole load exploded. The first two teams and waggons were destroyed.” Coining back io Arapuni, Mr Leggo said chat the main charge under the intake was laid in sealed kerosene tins ip. galleries so close to the river that the stones could be heard rumbling overhead. Blasting gelatine and gelatine dynamite were used because they are not affected by water. One pound to two tons of burden, four times the ordinary charge, was laid to so crumble the rock that it would wash away. The first shot; was a small one to lift the lip of the intake. Then the tunnel tilled with water, The purpose being to have the body of water behind the smashed rock after the outlet charge had been fired. For t his job on er 60 charges were laid in vertical pipes, an unusual system that was adopted to cur a channel and no more. The result was eminently successful, as also was the main charge at the intake, tired a week The Speed of T.N.T. A. T.N.T. fuse was used. The contraction stands for trinitrotoluene, a modern explosive, which has a detonating speed of no less than 17.500 feet a second, and which has so complete a detonating effect chat the power of the charges is enhanced. Before T.N.T, fuses electric detonators were used, hut as the effect of such detonators diminishes as it proceeds, very great technical difficulties would have had to be fared at Arapuni. As for the old gunpowder fuse, the speed of is ouly

two feet a mi mite, it would have been impossible to have fired two charges in perfect unison, much less (50. “It is a pity more people did not. know the speed of powder fuse," said Mr Lcggo. Also, they should know that the way to light it, is to apply the mutch when the phosphorus is itself exploding." Mr Leggo talked of the compounds of modern explosives, but the layman will hardly be interested. Yet it. is an arresting thought that ordinary glycerine which people rub on their chapped hands, becomes the agent of such terrific energy as is found in the modern explosive when treated with two acids.