Show PROPER SELECTION OF explosives the united states bureau of minos has just published bulletin 48 the selection of explosives used in engineering and mining operations by clarence hall and spencer P howell it deals with the characteristic features of the principal explosives plo used in engineering and mining operations erat ions and especially with the tests that show the suitability of different classes of explosives for various kinds of work the bulletin is published as one of a series dealing with tests of explosives and methods of reducing the risks involved in the use of ex explosives plo in mining work in large engineering projects and in mining operations requiring the use of explosives plo the selection of a suitable explosive from the many varieties offered for sale is of fundamental importance the various considerations involved in the selection of the proper class of explosives for the blasting to be done are given many explosives suitable for quarry work have been proven unsuitable for use in deep mines or in close workings in metal mining and in driving tunnels the character of the gases evolved by the explosive asive on detonation is an important consideration an explosive f for or use I 1 in n gaseous or dusty coal mines must be formulated and compounded so that its flame temperature and the height and duration of its flame are reduced enough to permit its being used with comparative safety in wet workings or in ill submarine blasting explosives impervious to moisture are requisite in extremely cold climates explosives that do not require thawing are desirable provided they are equally good in other respects an essential requirement of all explosives especially of those for use in tropical countries is that they shall remain stable without change in chemical or physical characteristics acte because of the varying conditions in the different projects on which explosives are used the fact is emphasized that some characteristics of explosives are of much importance in certain classes of work and of little or no importance in others As practically every class and every grade oi 01 commercial explosives is used in open air work to meet varying conditions the authors indicate the method of manufacture give typical composition of and state the use to which each of the following explosives plo is best adapted black lasting blasting powder granulated nitroglycerin powder 11 straight nitroglycerin dynamite low freezing dynamite ammonia dynamite and gelatin dynamite black blasting powder is stated to be iest best suited for work in which a gradual pushing or heaving effect is desired such as excavating cuts quarrying soft rock or stone and especially in quarries where large blocks of building stone are sought and in order to obtain the maximum efficiency fici ency the charge must be well confined by suitable stemming 0 granulated nitroglycerin powder is more effective and gives better results than black blasting powder in soft and seamy rock or in material that does not sufficiently confine the gases evolved straight nitroglycerin dynamites as a class develop greater disruptive force than any of the other commercial classes of explosives tested and for this reason they should be used for producing shattering effects or for b basting asting astin g very tough or hard materials whenever the conditions dit ions permit if the straight nitroglycerin dynamites are found to be too violent for certain classes of work the low freezing dynamites or the ammonia dynamites which have lower rates of detonation and hence less disruptive effect are recommended the slow freezing dynamites have the advantage of not freezing until exposed to a temperature of 35 degrees F or less but like all nitroglycerin explosives plo after they become frozen they must be thawed before use in order to insure the most effective results As the ammonium nitrate used in ammonia dynamite is deliquescent this class of explosive exposi ve absorbs moisture more readily than other dynamites therefore it is emphasized that care should be observed when storing this class of explosives in wet or damp places the gelatin dynamites have been used to a large extent in wet blasting such as in ill the removal of obstacles to navigation and in deep workings and as a general rule they are best suited for these purposes the products of combustion of explosives plo used in closed work are said to be of vast importance because in such work large quantities of explosives are genera generally aly used and they may produce dangerous quantities of poisonous gases on oil explosion the gelatin dynamite on detonation produce the smallest percentage percenta ge of poisonous gases but it is pointed out that this class clash of explosive is far from being satisfactory in this respect the bureau had a special gelatin dynamite made which on detonation produced no poisonous gases and it is believed that this illustration of the possibility of producing a gelatin dynamite that will not evolve Dois poisonous onous gases on detonation will WEI result in its being commercially merci ally manufactured this special gelatin dynamite was tested at the pittsburg testing station of the bureau in a limestone mine at west winfield pennsylvania and in a zinc mine at franklin furnace anew jersey the detailed results of which are arc reported in bulletin 48 the bulletin points out dangers arising from the burning of high explosives hy by showing the great grea t increase in the percentage of poisonous gases evolved the authors describe the methods of blasting followed at lock no 1 mon ougah onga hela ela river as an example of submarine operations giving the difficulties encountered showing the causes of MIS misfires f 1 re S and the methods used for overcoming these difficulties the tests incident thereto 0 showed that lariat variation lon in the cross sectional area of the bridge of an electric detonator was an im important factor in its failure to explode when in series with other electric detonators the bulletin closes with a table showing showing the relative potential energy disruptive effect which bears a close relation to the percussive or shattering force of explosives and propulsive effect which corresponds to the pushing or heaving force of mine explosives plo of different classes and grades glades |