The CHEMIST and CHEMICAL ENGINEER m the EXPLOSIVES INDUSTRY DAVID E. PEARSALL* Mellon Institute of Industrial Research, Pittsburgh, Pennsylvania
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ACH year the technical colleges and engineering schools of this country send forth a goodly number of young men trained in chemistry and chemical engineering who are ambitious to get positional opportunities in their chosen calling. Fortunate are the few who have an understanding of the conditions obtaining in any one of the many branches of the large and ever-growing process industries. Thus there is a need in the literature of a series of articles by specialists in the key industries, so that the student may gain a conception of the phases which relate not only to materials and equipment, but also to personalities, physical environment, and factors conducive to a successful career. A preview of an industry might tend to prevent what may later be termed a mistake in securing congenial and fruitful employment. The author having been associated with the explosives industry for a number of years herewith attempts to convey a rather broad but brief summary of the explosives field which, i t is hoped, will enable the young chemical engineer or chemist to locate the explosives industry as an integral part of chemical technology and a t the same time to give him sufficient information of a specific nature so that he may picture to himself what the industry is like and decide whether or not he might find it to his liking. The term "explosives" is synonymous to many with the word "war." The explosives industry to be described, however, is essentially a peacetime manufacture which has played a vital part in world progress. Ranking the American chemical and allied industries according to the value of their products made in 1936, the explosives industry would he placed about thirteenth in a list of thirty-one. This ranking does not include the related fields of ammunition and fireworks and also excludes the numerous other products manufactured by companies whose original business consisted entirely of explosives manufacture. The order that will he followed in discussing this subject will be as follows: (1) Types of explosives produced-what they are. (2) Manufacture of explosives, considering the various chemical and chemical engineering factors. (3) Testing of explosives.
* Industrial Fellow, Mcllon Institute of Industrial Research, Pittsburgh, Pennsylvania.
(4) The use of explosives. (5) Modern industrial significance.
I t should be stated here, that it is not planned to discuss those blasting methods which employ various mechanical devices or equipment, because such methods are outside the field of explosives being described in this article. TYPES OF PRODUCTS OF THE EXPLOSIVES INDUSTRY
The various kinds of explosives may be classified in a number of ways. For the purposes of this article they will he put in four groups, wiz., black powders, high explosives, smokeless powders, and blasting initiators. Black Powders.-Black powders are the oldest type of explosives known, dating back to about the early part of the thirteenth century. Their origin is variously ascribed to China, Germany, and England, there being no clear certainty on the subject. In England, Roger Bacon (1214-1294) is generally credited with the invention. Black powder consists of a mechanical mixture of sulfur, charcoal, and nitrate in the proportion found by experiment and use to give the desired results. A typical black powder for blasting contains about seventyfive per cent. nitrate, fifteen per cent. charcoal, and ten per cent. sulfur, together with small amounts of moisture, graphite, and an antacid such as calcium carbonate. For rifle powders, fuse powders, and other special uses, potassium nitrate is used in black powder manufacture because of its superior moisture resistance; these powders are termed "A" powders. Powders coutaining sodium nitrate are less expensive and are used extensively in blasting; they are known as "B" powders. " A and "B" powders are furnished in several differentgrain sizes. Other factors heing the same, the speed of the powder depends upon the grain size, the coarsest grains heing the slowest burning. Black powders are also supplied in pellet form. These pellets are usually about two inches long by one and one-fourth to two and one-half inches in diameter and are wrapped in a paper cartridge, there being four pellets to one cartridge. These cartridges, which have many advantages over the loose powders, have become quite popular.
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Commercial explosives are solid or liquid materials that can he instantly converted to large volumes of gas by such means as heat, friction, sparks, or shock. The explosive action may be caused by a progressive burning or by an instantaneous molecular rearrangement. Black powder is a ddagrating explosive, that is, i t is fired by ignition and the gases are generated progressively as the burning speeds through the charge. High Ez$losiwes.-In contradistinction to the burning type of explosives just described, high explosives are detonating explosives, i. e., they are fired by shock from a n intermediate agent or detonator and the transformation from solid to gas takes place with extreme rapidity as the shock wave is transmitted through the explosive. This is essentially a chain reaction. High explosives include all dynamites, gelatins, permissibles, and the low powders. The development of high explosives which has taken place in the last hundred years, has been marked by the introduction of nitrocotton in 1845, nitroglycerin in 1846, detonators in 1864, dynamite in 1867, and gelatins in 1875. Most of these advancements emanated from Nobel, the Swedish chemist. Before discussing the high explosives, i t will be necessary to define explosive "strength," which refers to the power or force developed hy the explosive when it is used. The strength rating is based on the nitroglycerin content of the straight dynamites; i. e., a forty per cent. strength straight dynamite contains forty per cent. nitroglycerin and any other forty per cent. dynamite has a disruptive force equal to the forty per cent. straight dynamite weight for weight. This does not mean that the relative energy of a sixty per cent. dynamite would he twice that of a thirty per cent. dynamite because the ingredients other than nitroglycerin and sodium nitrate which enter into the composition of dynamite have some explosive strength of their own when mixed with nitroglycerin. Thus the actual measured strength of an explosive is not directly proportional to the amount of nitroglycerin in i t and is determined experimentally. Dynamites are mixtures of nitroglycerin and absorhents. The first dynamites made by Nobel used the inert absorbent kieselguhr, while modem dynamites contain combustible absorbents and other explosive ingredients. Dynamites are of several types known as straight, extra, low freezing, and so forth. At present almost all dynamites are low-freezing, representing a most important step in the development of explosives, as in times past much trouble and many accidents were attributed to frozen dynamites. Ordinary nitroglycerin is not a nitro body but glycerol trinitrate and has a freezing point of about 13'C. This freezing point is lowered by replacing part or all of the nitroglycerin by aromatic nitro-compounds such as DNT or mixtures of DNT and TNT, by related nitric acid esters such as dinitroglycerin or the polymer tetranitrodiglycerin and nitrated sugars, and by ethylene glycol dinitrate. Straight dynamites are composed of nitroglycerin, sodium nitrate, wood pulp, and a small amount of an antacid. Extra dynamites are those in which am-
monium nitrate partly replaces the nitroglycerin. Straight dynamites are quick acting and have a high shattering effect or brisance; extra dynamites have a slower speed of detonation and produce less shattering. The wood-flour is present as an absorbent for the nitroglycerin, hut takes part in the explosive reaction. Both the straight and extra dynamites are produced in strengths varying from fifteen per cent. to sixty per cent. Nitroglycerin may be gelatinized by the addition of a certain amount of nitrocellulose; e. g., eight parts nitro-cellulose completely gelatinize ninety-two parts of nitroglycerin and form a plastic elastic colloid which is known as blasting gelatin. This explosive is of practically one hundred per cent. strength and has high brisance. As the gelatins had may advantages over the dynamites, especially for wet work, means were soon sought to modify their explosive force so that they would be more generally useful. This was accomplished hy adding various dopes to the gelatins and by using less nitrocotton in gelatinizing the nitroglycerin. These developments are known as gelatindynamites and are also quite plastic. The gelatindynamites are furnished in twenty per cent. to ninety per cent, strengths. The semi-gelatins are still later developments; they retain some of the plasticity of the gelatins, but a t lowered costs. They consist mainly of ammonium nitrate with only sufficient gelatinized cotton to make them cohesive. Permissibles are explosives that are similar in all respects to samples which have passed certain tests prescribed by the United States Bureau of Mines to determine their suitability for use in gassy and dusty coal mines. All explosives when fired produce a flash or flame, which varies in length, duration, and temperature. Black blasting powder gives the largest and longest lasting flame; dynamites give much hotter flames hut they are smaller and exist for a shorter time. Permissible explosives are specially designed to yield a small flame of brief duration and low temperature. Thus, if they are used in accordance with the prescribed conditions, there is little likelihood of gas or dust ignitions taking place. Most of the present-day permissibles are of an ammonium nitrate or a gelatin base. One of the newer developments in explosives is the socalled high-count explosives. These are dynamites or semi-gelatins containing special carbonaceous materials as absorbents which make the dynamites more bulky and raise the cartridge counts in some cases from as low as 300 to 500 per one hundred pounds of explosive. Many of these low-density explosives are permissihles. The cartridge count of explosives is frequently used as the measure of their density. There are also the so-called "low" or hag powders, which are dynamites of low strength varying from five per cent. to twenty per cent.; i. e., they are intermediate between the black powders and the high-explosive dynamites. It will have been noted that the active ingredients of high explosives are based on the use of nitric acid esters
and aromatic nitro compounds in ceneral and on nitroglycerin in particular. -One class-of compounds that has found commercial outlet is the nitrostarches. The nitrostarches overcome one objection of nitroglycerin explosives in that they produce no headaches when they are used; however, they may possess certain undesirable features and are not extensively manufactured. Nitramon is a new development in the explosives field. This explosive consists of canned ammonium nitrate which has a small amount of a sensitizing agent added to it and which is packed in the can to a definite density. This explosive is extremely insensitive and requires a special priming device to detonate it. On this account it possesses unusual safety features. In addition to the classes of explosives described, there are various other types which appear on the market from time to time. Some of these are based on the use of potassium chlorate as the oxidizing agent and many of them have proved unsatisfactory and dangerous. It is interesting to point out that the perchlorates have largely replaced the chlorates because they are more stable and less sensitive, although they contain more oxygen than the chlorates. Smokeless Powders.-The smokeless powders, which are propellants, consist essentially of two types, uiz., the single-base or solvent colloided nitrocellulose powders, and the donble-base powders in which certain amounts of nitroglycerin are used along with the nitrocotton. In addition, inorganic nitrates, inerts, and stabilizers such as diphenylamine are added. The speeds of these powders may he varied and controlled by the use of accelerators (such as nitroglycerin) and of retardants which may be plasticizers of nitrocellulose, e. g., triphenyl phosphate. The powders are made in both fast- and slow-burning varieties, the fast powders being used in shot-gun shells, while the slower ones are for rifle and military propellants. The burning speeds are also controlled by the sizes and shapes of the powder grains or pellets. Blasting Initiators.-There is another class of explosive compounds known as detonating materials that has high hrisance, velocity, and sensitivity. These materials are used to initiate the explosion of other less sensitive explosives, such as the blasting and propellant powders. The detonating materials are used either alone or in mixtures, and are enclosed in caps or tubes, known as detonating caps, and detonating fuse for use with blasting explosives, and percussion caps for use with ammunition. The blasting cap usually contains mixtures of fulminate-chlorate or azide-nitrates; modem caps frequently have a base charge of a material such as tetryl, or nitromannite in addition to the initiating charge. The explosives used in detonating fuses are as powerful as those used in caps, but are relatively insensitive and require a cap for detonation. These fuses contain such compounds as (1) phlegmatized fulminate, (2) picric acid (melinite), (3) TNT (tritol), and (4) PETN (pentrit).
MANUFACTURE OF EXPLOSNES
The manufacture of explosives, which will now be considered, should be of special interest for it is diflicult to conceive of an industry in which the need of technical men is greater than in the explosives field. F i s t , the chemical engineering factors present in explosives manufacture will be discussed, following which flowplans for the manufactnre of black powders and of dynamites will he briefly described. Chemical Engineering Factors.-The chemical engineering factors that enter into explosives manufactnre are the same factors that enter into all chemical manufacturing; however, here they find limiting conditions and special situations to a greater.degree than in most of the allied industries. Let us consider these factors under the following divisions: (1) plant locations, (2) construction and materials of constmction, (3) unit processes, and (4) plant and health hazards. The manufacture of explosives in this country dates back to colonial times when the supply of powder could no longer be obtained from England and when it came into great demand. Thus numerous black powder plants were erected mainly in the eastern part of the iand. As the general development of the country took place westward, powder manufacture likewise went westward until today there are explosive plants located all over the nation. These plants, however, are usually located so that they are near various mining operations, which are the largest users of explosives. In 1936 there were twenty-two different manufacturers of explosives in the United States, operating about seventy-four plants. The greatest concentrations of these plants were in Pennsylvania (ten per cent.), California (ten per cent.), and Illinois (five per cent.). On account of the nature of explosives, the plants are always located in rather isolated spots so that they are not a menace to the surrounding territory, and likewise so that their surroundings are not detrimental to them. Locations are chosen if possible, that have natural bamcades such as hills, slopes, and so forth; however, if natural harricades are not present, artificial ones are placed around each building so that an explosion in one building will not be communicated to the others. The nitroglycerin plant is frequently located on a hill so that gravity flow may be used. Locations are selected first with a view to safety, and second to economy of operation. This is also true of the magazines in which the explosives are stored. The distances between buildings are governed by the American table of distances, set up by the Institute of Makers of Explosives. One hears a great deal about materials of construction, and in an explosives plant not only a knowledge of materials is required but also sufficient engineering to construct the buildings themselves and the equipment in them. Here again the factors of safety and economy of operation govern design. The huildings are so designed that, should an explosion occur, a minimum of damage will result. This is accomplished in various ways, one of which is to build rigid or reenforced walls,
and to have a light roof. The inside walls will he smooth so that dust will not accumulate, and they may also be curved and shaped. If an explosion occurs, the walls will deflect the explosive wave so that it will he away from the operators and equipment and will blow off the roof or other lightly constructed section. Barricades are also placed around machines; in some operations the machines are operated from behind barricades, using a system of mirrors to view the operation if this is necessary. Wood is utilized to a large extent for construction; also non-sparking metals and insulating materials are used wherever possible. As both sulfuric and nitric acid plants are usually located with a dynamite plant, much lead and glass-lined equipment is also used.' In nitroglycerin and dynamite manufacture, special precautions must be taken so that the equipment does not absorb the nitroglycerin, as many accidents have occurred when the equipment is being replaced or repaired. The explosives industry is primarily one of unit processes and unit operations, each of which is segregated from the others. Hence, it tends to he a batch type rather than a continuous flow type operation. In the manufacture almost every type of chemical engineering, processing and equipment is met with. This will he amplified later on in the discussion of the flowplans for the manufacture of black powders and dynamites. In the explosives industry plant and health hazards are watched perhaps more closely than anywhere else, and every known precaution is taken. As already described, great care is taken in selecting the plant location and in the plant huildings and equipment. Special caution is exercised on all moving parts, and equipment drives, such as motors, are explosion proof and in addition usually placed in separate buildings from where the equipment is operating. All machines are insulated and grounded to prevent static electricity accumulations and danger from lightning discharges. Explosion-proof lighting fixtures are used in the buildings and all buildings and equipment are painted white or a light color and kept scrupulously clean from dust and accumulations of waste material; hence the name of "white area" or "clean area" for the parts of the plant in which explosives are actually made. Matches and cigarette lighters are not permitted to be carried into explosive plants and must he deposited a t the entrance where they can he reclaimed on leaving. All plants are guarded by watchmen and are enclosed by fences. All workmen in danger areas wear special shoes or rubbers and special clothes or overalls changed before leaving the plant. Some operations, such as incorporating or wheeling hlack powder, are always conducted without an operator being present in the building, the machine being controlled from remote switches. In other operations, the number of men present is limited. Nitroglycerin has a powerful physiological action which causes violent headaches, either from handling it when it is absorbed by the skin, or by breathing the va-
pors, because it is slightly volatile at ordinary temperatures. Most persons engaged in nitroglycerin explosives work rapidly establish an immunity to its effects although this immunity is quickly lost by an absence of a day or two from nitroglycerin work, and must be reestablished when the work is resumed. The aromaticnitro bodies have definite toxic effects and great care must be observed by the workmen in their manufacture. Some of these nitro-compounds, such as picric acid (TNP), color the skin and hair yellow, which color cannot be washed off but will gradually disappear when absent from the piaic acid. These compounds also produce a dermatitis in certain people who have sensitive skin. The toxicity of DNT was brought out not long ago when it caused numerous cases of blindness among women who were taking an antiobesity remedy containing it. I t is, therefore, apparent that the management and the workers of an explosives plant must be continually on the alert to prevent any of these various potential plant and health hazards from becoming actualities. That they are successful in doing this is attested by the splendid records of their low accident and occupational disease rates. Flmw-Plans for Manufacture of Black Povders and Dynamites.-Black powders are made much the same way today as they were one hundred years ago. However, some technical changes have taken placc, such as improvements in the- type of equipment used. The flow-plan of hlack powder manufacture is as follows. The sulfur and charcoal are usually premixed in hallmills and then added to the wheel-mill along with the nitrate. The wheel-mill or edge-runner has two large diameter runners, each weighing several tons. These runners are usually made of iron and frequently the bed-plate is also of iron, in which case the runners must he suspended and not actually rest on the plate. The ingredients are milled until thoroughly uniform, the operation being referred to as incorporation. The product known as wheel-mill cake is taken from the mill to the press-house. In the press-house the larger cakes are broken between rolls and a press charge is then built up. The press consists of a number of plates and frames, the latter being filled with the broken up wheel cake. When assembled, it resembles a plate and frame filter-press. The pressure is usually applied hydraulically. After pressing, the cakes are removed from the press and frames and taken to the corning-mill. This mill consists of a number of pairs of breaker-rolls having various sized corrugations and so arranged with conveying belts that the cakes are gradually and automatically reduced in size to the desired limits. The powders are then sieved in rotary screens and finally taken to the glaze-drums, which are large horizontal drums made of wood. These drums hold several of the wheel-mill or press-charges so that a certain amount of blending takes place. The drums are revolved until the moisture conditions are right, when graphite is added and the rotation continued until a satisfactory graphite glaze has been applied to the grains. Follow-
ing this operation there is further blending and then packing. A typical flow-plan for the manufacture of nitroglycerin dynamite is as follows. The glycerin and mixed acid are added to a nitrator fitted with cooling or refrigerating brine coils. A drowning tank is always placed below the nitrator so that the entire charge may be quickly emptied into it should the reaction become uncontrollable. Following the reaction, the nitroglycerin and spent acid are run off into a separating tank, from which the spent acid goes to a settling tank for removing traces of nitroglycerin and then to the acid recovery system. The nitroglycerin goes to a water washing tank, then to a neutralizing tank containing sodium carbonate solution, and finally to a storage tank. As previously described, dynamites consist of nitroglycerin and various other absorbent and explosive ingredients. These other ingredients, termed "dope," consist of wood flour, sodium nitrate, sulfur, and so forth. All the dope ingredients are weighed out and then placed in a suitable dryer; after drying they next go to the dope mixer. The dried and mixed dope and nitroglycerin are then brought together in a dynamite mixer. These mixers may be made of wood, bronze, or other non-sparking material and contain mechanical agitators. In the manufacture of gelatins and gelatin dynamites the operations are similar to those described except that the nitroglycerin is first colloided with the nitrocotton by agitation and heat. The jelly is then taken to the mixer. Often the tank used for colloiding the nitroglycerin is mobile and is taken to the mixing house where the agitators are lowered into it. WernerPfleiderer type mixers are frequently used for viscous gelatins as they give a kneading action similar to a dough-mixing machine. Various other type machines are used for the less plastic gelatins. After the mixing the dynamite or gelatin dynamite is ready for cartridging. Paper cartridges are formed on a special machine which crimps one end and permits the other end to remain open. These cartridges are usually paraffined and then taken to the pack houses. Packing in the cartridges is now accomplished automatically for both dynamites and gelatins, although most of the gelatins were formerly band-packed. A Hall-type dynamite packing machine is constructed mainly from wood. This machine has a member rotating on a horizontal axis and contains four chambers or shuttles. The rotation of the shuttles is intermittent by quarter-turns; the sequence of the operation is inserting the paper shells, packing them from above with dynamite, closing and folding the ends of the cartridges, and removing the filled and crimped cartridges. The daily output of one of these Hall machines is quite high. The gelatin dynamite packing machines are frequently semi-automatic and the explosive is forced from a hopper through a multiple nipple plate by means of a worm or hydraulic pressure. The gelatin is extruded directly into the preformed paper shells and the ends are crimped automatically. A worm type machine is less efficient than the hydraulic piston type.
TESTING OF EXPLOSIVES
The testing of explosives constitutes an important branch of the explosives industry and employs a great many technical men; who are usually chemists, physicists, and chemical engineers. This testing may be divided into chemical tests and physical tests. Chemical Tests.-All explosive plants have routine chemical control laboratories which are constantly analyzing the raw materials going into the process, to insure that they meet quality and strength specifications. These laboratories also furnish information for strengthening the spent acids, and analyze samples of completed products. In addition, the explosives companies have central research laboratories where new explosives are evolved, old ones improved, and all complaints and competitive explmsives examined. The explosives chemist must be an expert analyst on both gravimetric and volumetric methods. Materials used in explosives are composed entirely of two classes, viz., (1) those that give off oxygen when they undergo reaction, and (2) those that take up oxygen. Thus in designing an explosive it is attempted to control the relative proportions of these two classes so that a neutral or slightly positive oxygen balance is obtained. In making these calculations the oxygen balance of the paper shell and its paraffin coating is taken into account as well as the dynamite ingredients. With a proper oxygen balance, the gases given off by the explosive are composed almost entirely of carbon dioxide, nitrogen, and water. When a powder is not properly balanced carbon monoxide and oxides of nitrogen are found in the gases of decomposition, and, as these gases are extremely toxic, they are objectionable for use in closed areas such as mines. Gas analyses are always made to determine the products of combustion, and at times the solids products of combustion, if any, are also analyzed. Physical Tests.-In addition to the chemical tests, complete physical tests are made on explosives to determine their explosive properiies. Some of these tests will now be described briefly. The pressure dweloped is ascertained by exploding a measured quantity of explosive in a pressure bomb known as a Bichel Gage, which is fitted with a pressurerecording gage similar to the Crosby engine indicator, the drum with chart being revolved a t a definite speed by an electric motor. The actual strengths of the explosives are determined by means of ballistic pendulums or ballistic mortars. These strengths are sometimes referred to as "unit deflecting charges" and represent the weight of an explosive that will produce a deflection of the pendulum to the same degree as a standard weight of a standard explosive. The ballistic pendulum consists of two parts, (1) a cannon in which the explosive is fired, and (2) a pendulum which receives the impact of the products of explosion and stemming. The ballistic mortar is similar to the ballistic pendulum except that its weight is much less, and the explosive is stemmed with a cylindrical steel shot which is projected from the mortar.
Other factors being the same, the velocity or rate of detonation of an explosive determines its shattering effect. The velocities are measured in several ways, the most common one being the use of the Mettegang recorder. This consists of a soot-covered rotating drum, a vibration tachometer for measuring the speed of the drum, and an induction coil with terminals so connected that it projects sparks on the soot-covered drum. Wires inserted a t measured distances apart in the explosive are connected to the recorder, and the time interval between the rupturing of the two wires is found from the marks on the rotating drum. Another method of recording the velocity is by means of a special camera having a rotating drum on which a film is attached, or by a camera having a stationary film and a revolving mirror. A third and relatively simple method of measuring velocities is that of d'Autriche, in which the unknown explosive speed is compared to that of a detonating fuse of known speed. Other physical tests, all of which require special equipment, are those for determining (1) impact sensitivity, (2) friction sensitivity, (3) duration and length of .flame, and (4) the measurement of the pressure waves sent out by an explosive. This latter is found by means of Schlieren photography, which depends upon changes in the refractive index in the air caused by the explosive pressure wave, and is recorded by the camera through the deviation caused in a restricted system of light rays.
drilled holes a t the mine face and pushed into position with a wooden pole, the fuse extending well beyond the face. Other dynamite cartridges are pushed into the drill-hole until the required number is obtained. This operation is followed by the plugging of the hole, usually with clay or other handy, easily packed material, which is called tamping or stemming. The tamping eliminates the dangers of a blown-out shot and increases the efficiency of the explosive. The position of the priming cartridge varies, but is frequently next to the last cartridge put in the hole. Various advantages are claimed for the different positions in which it is placed. When black powder is to be ignited by means of fuse, it is not necessary to use a detonating cap. Fuses are ignited by means of special lighters of various types or by open lights. In the electric method of detonation, electric blasting caps or E. B. caps, as they are commonly called, are used in place of fuse and caps. These caps differ from fuse caps in that they are sealed and have two leg-wires extending from them by which means they are connected to a source of current and to various electrical hook-ups. The present-day caps are of the low tension type, in which a platinum bridge-wire is heated to incandescence and thus ignites the priming and detonating compounds in the caps. Some explosive makers surround this bridge-wire with a match-head composition which ignites the cap charges. . In the early development of E. B. caps, high-tension caps were used in which the ignition was supplied by a spark jumping from one terminal wire to another. Primers are prepared the same THE USE OF EXPLOSIVES as for fuse and cap blasting and the holes are loaded in A study of this industry would he grossly incomplete the same manner. The circuits are connected in variwithout reference to the uses of explosives. This is ous ways, and batteries, blasting-machines (dynamos) most readily accomplished by considering briefly first and power circuits are used for ignition. the methods of using explosives, and, secondly, the With fuse and cap blasting, i t is difficult to cause a number of holes to go simultaneously; on the other fields in which explosives are employed. Methods of Using Explosives.-The early use of ex- hand, i t is quite easy to have a rotation of shots in any plosives was attended with many dangers, one of the desired order merely by trimming the fuses to different greatest being caused by the lack of a good means of lengths. To secure rotational firing with electric caps providing a time interval between applying the fire and it is necessary to use special delay caps which contain the subsequent explosion. This problem was solved burning elements between the bridge-wire and the in a very satisfactory way by the Englishman, William detonating compounds. These elements may be pieces Bickford, in 1831 through his invention of safety fuse. of fuse, or metallic cylinders containing either black A safety fuse consists of a powder train surrounded by powders or thermite powders. A third method of blasting that has become quite various textile and waterproofing materials, and presents the appearance of an insulated electrical wire. prevalent ih the last twenty years, particularly for large The fuse has the purpose of carrying fire to the charge quarry shots, is that in which detonating fuse is used. a t a predetermined and uniform rate. Although pres- In this procedure, lines of the Cordeau detonant are ent-day fuses are still made on this same principle, they placed the length of each hole and then connected to have been greatly improved in all respects, and have central lines, one of which is joined to either a cap and remarkable burning regularity under various conditions fuse or else to an electric-blasting cap. In this way no of use. When safety fuse is employed in blasting, the detonating caps are placed in the holes thereby increasmethod is referred to as the fuse and cap method. To ing safety; also less explosive is needed as the detonatinitiate a charge of dynamite, a detonator is crimped on ing fuse increases the force of the cartridges by about the end of a piece of fuse of required length. This fifteen per cent. Although the holes will fire in their capped fuse is inserted in a dynamite cartridge after a proper sequence, the effect is that of an instantaneous hole has been punched in it. The fuse is then tied shot. This effect is attributable to the fact that the to the dynamite cartridge aud the assembly constitutes velocity of the detonating fuses ranges from 5000 to what is known as a primer. The primers are placed in A000 meters per second. The maximum detonating
velocity of a gelatin is about 8000 meters per second, while the various semi-gelatins and dynamites range in velocity from about 3000 to 7000 meters per second. These figures compare with speeds of 3500 meters per second for a No. 6 blasting cap, 6000 meters per second for nitrocellulose powders, and 300 meters per second for black powder. In considering velocities, it must be borne in mind that the velocities are controlled to a large extent by the densities of the explosives, an increase in density resulting in an increase in velocity. The velocities are also affected by the degree of confinement in the borehole and the initial detonating impulse. It is this control of the velocity that permits the adapting of the explosives for different uses. Consumers of Exfi1osives.-The bulk of explosives produced in the United States are consumed chiefly by the mining, quarrying, and construction industries. However, they are also used in less quantities for agricultural work, in lumbering, in producing oil-wells, and in demolishing old buildings. According to the United States Bureau of Mines Report of Investigations No. 3350, the production of explosives in the United States in 1936, listed according to classes, was as follows. High explosives Pemissibles
approximately approximately approximately
82,000,000 lbs. 262,000,000 Lhs. 48,000,000 lbs.
Total
approximately
392,000,000 lbs.
Black powders
The use of these explosives is approximately accounted for by the information given in Table 1. TABLE 1 Block lndurl~y
bowdrr
Coal mines Metal miner Quarries and "on-metallic mineral miner Railroad aod other eonsfruetion Miecellaneour
87 1
3 0
-
High Pwmirsiblc ex$loriurr (in fie" ud.) 98 2' 29 1 19 38 1 5
New Uses for Exfi1osives.-New uses for explosives are constantly coming to light. Two of the most important of these are (1) in geophysical prospecting, and (2) in accelerating swamp fill. Geophysical prospecting, or exploring down as it is sometimes called, is a method of determining and plotting the sub-structure from the surface of the earth. When an explosive is detonated it sets up seismic or elastic earth waves so that it is comparable to a miniature earthquake, and seismographs record these waves. If the vibrations of these waves are recorded from a distance, it will be found that a part of the energy travels a t the ground surface, a part is refracted should there be a harder medium below, and a part will be reflected from the interface between the formations. Therefore the two methods of prospecting are known as refraction and reflection. By measuring, the speed, magnitude, and character of these waves a knowledge of the substructure is obtained, and it is possible to predict the
location of sulfur, salt, oil, gas, and metals with considerable accuracy. Modern highways are frequently built over swampy and marshy land on which it is impossible to obtain a satisfactory permanent footing. By exploding charges of dynamite in such areas, the muck, or other unstable material, is blasted away to permit a fill to be placed on a firm, hard, bottom which will result in a permanent stable roadbed. MODERN INDUSTRIAL SIGNIPICANCE
The history of civilization is closely linked up with the history of the explosives industry, and for almost every advance made in explosives development corresponding progress has resulted in the advancement of man's physical environment. Civilization as we know it today would have been impossible without the aid of explosives, and i t is only through their use that the mining industry and the metal industry have gone forward to their present positions. In the United States 62,000 ounces of silver were produced in 1860. Nobel made the first dynamite in 1867; by 1870 the output of silver advanced to 10,000,000ounces and in 1936 the production was almost 63,000,000 ounces. In 1869, before dynamite was regularly adopted for mining of copper ore, the production was 72,000 tons, while in 1935 about 19,000,000 tons of ore were mined. These figures, of course, vary with general industrial conditions, but it can be readily realized that the tremendous advances made since the middle of the nineteenth century would not have been possible without the use of explosives. Growth of Exfilosiues Industry.-In the early days of explosives manufacturing history there were numerous small manufacturers. During the latter half of the nineteenth century and around the early part of the twentieth century a period of general business expansion took place, in which many small companies were absorbed by the larger ones. The explosives industry shared in this expansion. By 1907 the Government considered that the du Pont Company dominated the explosives manufacturing field and instigated suit under the Sherman anti-trust act. In 1912 the du Pont Company was dissolved into the three companies, viz., (1) du Pont, (2) Atlas, and (3) Hercules. These three companies, together with the explosives division of the American Cyanamid and Chemical Corporation, which division was organized in 1933, are the largest presentday manufacturers of explosives; accordingly the modern growth of this industry has taken place during the past twenty-five years. Both the Atlas and Hercules Powder Companies celebrated their twenty-fifth anniversaries last year. The Hercules Powder Company in its anniversary booklet called "Looking A h e a d states that the original markets in mining, quarrying, and construction are relatively the same today as they were twenty-five years ago, i. e., the annual poundage of explosives produced has remained practically constant, although these industries have increased apace
with the general industrial expansion in the last quarter centurv. This situation in fact exists onlv because mode& explosives have been so improved that they do more work per pound than the older ones. The major powder companies have, however, undergone tremendous growths since 1913, which can be attributed to diversification of the products manufactured with corresponding expansions in their markets. Today these companies are leaders in the chemical industry which speaks well for the farsightedness of their managements and the ability of their technical personnel. Ofifiortunities in the Exfilosinres Field.-There are .. many opportunities for technicians, particularly chemists and chemical engineers, in the explosives field. Like the other Drocess industries.. ex~losivesmanufacture is carried on with relatively few workmen. There are also few supervisors and consequently they have greater responsibilities; hence there has been a trend toward placing technical men in all supervisory positions. On becoming associated in the operating, development, or research branches of an explosives company, i t is customary to give the employee a training course. After this course, the man may remain in research and development work or he may be sent to one of the explosives plants as chemist. The line of advancement in the operating end would be from chemist A
to chief chemist, to supervisor, to assistant superintendent, and then superintcndcnt. Should the individual remain in research or technical work, the advancement would be in having greater responsibilities and being placed in charge of certain new developments. Many of the department executives a t the home offices of the companies have been chosen from among the research and development men. A third line of opportunity exists in the sales end. Most of the explosives salesmen are technically trained men who have become qualified to give expert blasting advice and see that the proper explosives are used and that they are applied correctly. In addition to the explosives companies themselves, there are opportunities for work on explosives in the mining industry and with the United States Bureau of Mines. Perhaps there may be some readers who are sufficiently interested in the subject of explosives to wish to learn further concerning it. For the benefit of such, a selected bibliography is included below. The literature on explosives is not particularly comprehensive and much that has been written is in foreign languages. Realizing that the difficulty incidental to translating an unfamiliar subject often causes the reader to lose the true meaning of the matter at hand, all oi the subjects we have listed in the bibliog~aphy,with two exceptions, are English originals or translations.
SELECT BIBLIOGRAPHY OF EXPLOSIVES (14)
Books (1) 0.. "The manufacture of eu~losives."The Mac. . GUTTMAN. millan Co., New York City, 1895,2 vds. (2) BRWNSWIG, H., "Explosives," translated by C. E. MuNRor and A. L. KIBLER,John Wiley & Sons, Inc.. New York 2.. L.LJ,
(3)
In19 . 7 . A .
ESCALES, R., "Schwarzpulver und Sprenpsalpeter," Verlae
PAYMAN, W. AND D. W. WOODHEAD, "The pressure
wave
sent out by a n explosive, Part 111, spark photographs with permitted explosives," Safety in Mines Research Board (British) Paper No. 99 (1937). W.. W. C. F , SHEPHERD, AND D. W. WOODHEAD, (15) PAYMAN, "High speed cameras for measuring the rate of detonation in solid explosives," Safety in Mines Research Board (British) Paper No. 99 (1937).
Articles COLVER,
E.
DE
W., "High explosives," D. Van Nostrand
Cn . NPW i t ~l.O l R -- , - - Vork C .~.>,
VAN GELDER,A. P. AND H. SCHLATTER, "Histmy of the explosives industry in America," Columbia Universitv Press, New York City, 1927. NAOUM, P., "Nitroglycerin and nitroglycerin explosives," The Williams & Wilkins Co.. Baltimore. ~,Marvland. 1928 LA M o r ~ e A., , "Blasters handbook," E. I . du Pont de Nemows & Co., Wilmington, Delaware, 9th ed., 1938. ~
(20)
C. HALL,
AND
Bulletins S. P. HOWELL, "The selection of explosives
used in eneineering & mining operations." U. S. Bureau of ,.T^ L."",
"0
llnl",
(22) (23)
-0 {LzrLT,.
-
STOW,C. G., "The I analysis. of.permissible " " .-., ~ explosives." U. S. Bureau of Mines a u u e t ~ nluo. YO (IYIOJ. TAYLOR, C. A. AND W. H. IIIN~ENBACH, "Explosive-their materials. constitution. a n d analyses," U. S. Bureau of Mines ~ d l e t i n N o219 . (1923). PERR~TI, G. S. AND J. E. TIFZANY, "The effect of substituting ethylene glycol dinitrate in permissible explosives," U. S. Bureau of Mines Report of Investigation No. 2935 ,,om,> \"'",.
(21)
(13) MUNROE, C. E. AND J. E. Bulletin No. 346 (1936).
TIFFANY, U. S. Bureau of M i n e
(24) (25)
MAJRICR, A,. "Detonating fuses of commerce," Chsm.Zlg., 60. 333-5 (1936). B A ~ ~ H U ST: , dynamite-the new Aladdin's lamps," Hercules Mixer, 4 (April and M a y , 1922). SCHLATIER, H., explosive^ 1876-1926," Ind. Eng. Chem., 18.905-7 11926). KERSHAW, S . safety in the manufacture of nitric acid, sulfuric, and mixed acids and nitrate or ammonium as used in the manufacture of explosives," ibid., 18, 4-9 (1926). LA MOTTE,A,, "High explosives." C k m . Met. E n g , 36, 460-3 (1929). BARAB.J., "Dynamite-Forerunner of Progress," E&osines Engineer, 14, 1 3 5 4 (1933). "Introducing nitramon," Du Pont Magazine. 29, 5-7 (1935). W?ODBURY, C. A. AND W. C. HOLMES, "Commercial exploswes industry,'' Ind. Eng. Chenz., 27, 632-7 (1935). MUNROE, C. E. rn J. E. TIFFANY, "Testing permissible explosives," ibid., 27, 655-8 (1935). MACNAB,W., "Chemical engineering in explosives manufacture." Trans. Inst. Chem. Enys. (London), 13, 9-13 f19.15\ ~--..,.
(26) HEILAND. C. A., ''Exploring with explosives," Ezplosives Engineer, 13 (1935). (27) BAW, J., "Modern explosives in industry," Mining Congr. 3.. 22, 5&7 (1936). B. L., "Dynamite strengths," Erplosives Engi(28) LUBELSKY, We?, 14, 361-5 (1936).
