"POLAR" TYPES

Evening Post, Issue 13, 16 January 1936, Page 6

"POLAR" TYPES

NEW EXPLOSIVES

PREVENTING ACCIDENTS

It has been decided by the Government that, in the interests of public safety, a modified non-freezing type of explosive, employed in mining and for other similar purposes, would in future be supplied for the New Zealand market. With that end in view, negotiations were recently concluded with Nobels (Australasia) Proprietary,l Limited, the firm which supplies practically all the explosives used in New Zealand. The Minister of Internal Affairs <the Hon. W. E. Parry) stated yesterday that the' decision was come to as a result of rigid tests made by State experts. The position now would be that the lead given by Great Britain would be followed. In future j only the "Polar" types of explosives | would be approved for importation into New Zealand, except for special purposes. The Minister explained that one of the physical properties of nitro-glycer-ine, which is the basis of most of the "high" explosives, such as gelignite and blasting gelatine (as compared with ordinary gunpowder, which is technically a "low" explosive), was that this material froze at a temperature of 40deg Fahr., or Bdeg above the freez-ing-point of water. In the frozen condition the explosive was very irregular in its action, being sometimes extremely insensitive and failing to explode in the bore hole, and on other occasions capable of being detonated by a comparatively minor shock. WINTER ACCIDENTS. / The departmental records showed that the number of accidents occurring in the use of explosives was always higher during the winter than in the summer months. It was probable that the majority of these accidents were due to the explosive used being either frozen or in a "chilled" condition, in which it was less sensitive than normally to explosion by a detonator. The standard practice recommended by the makers when explosives were found to be frozen was to thaw them in a water-jacketed pan, hot water being used. Despite continual warnings, however, miners and other users adopted tmsafe methods of thawing' which resulted in accident. A case of this sort, for instance, occurred at Halcombe in July last, where a house was wrecked and all the occupants injured owing to the placing of frozen explosives in the kitchen oven to thaw. . For many years past technologists: had been experimenting with different materials in an attempt to obtain an explosive of equal strength to the standard variety which was not subject to freezing. Anew type of explosive had lately been introduced in .which the glycerine used in the manufacture of nitro-glycerine was partly replaced by a proportion of ethyleneglycol. It was found that the resulting explosive froze at a much 'lower temperature than ordinary nitro-gly-cerine, and experience had shown that the modified explosive would resist without freezing the severe winters in countries such as Canada.

In Great Britain the regulations under the Explosives Act had been amended to provide that only the lowfreezing explosives, or. as they are known in the trade, "Polar" explosives, may be used, and negotiations were undertaken about two years ago by the officers of the Mines, Public Works, and Internal Affairs Departments, with .the representatives of the explosives company with a view to similar provision being made in New Zealand.

One of the difficulties met with was that part of the explosives used in New Zealand are manufactured in Victoria, and as ethylene-glycol was not manufactured in Australia it would be necessary to import this, and the cost of the low-freezing explosives would therefore be slightly higher than that of thie ordinary nitro-glycerine types. As a result of further investiagtions, a compromise was reached. under which it had been found possible to supply this market with the low-freezing explbsiyes without any, increase on the previously existing prices. TESTS MADE. A sample consignment of Polar explosives, including gelignite, blasting gelatine, and samsonite (the latter being a special explosive used for coalmining) was imported into New Zealand at the beginning of last winter. These samples were sent to the mining areas in the South Island, where they would be subject to extremes of temperature, and from time to time during the winter the samples were tested against the ordinary explosives. An inspectional visit to these localities has since been made by the chief I inspector of explosives, together with a representative of the explosives company. The inquiries made showed that the Polar explosives had stood up in an excellent way to all the tests, and had "shown no signs of freezing,' even when exposed in the open air to hardfrost conditions. The power of all types of this explosive was found to be equal, if not superior, to those now in use.

The Minister added that, as an old miner, he realised to the full the value of the advance which had been made in the production'of a non-freezing explosive, and he had little doubt that the use of the improved type of explosive would result in much greater freedom from accident in future.