EXPLOSIVES 390 CHIMIA 2004, 58, No. 6

Chimia 58 (2004) 390–393 © Schweizerische Chemische Gesellschaft ISSN 0009–4293

Commercial High Explosives

Otto Ringgenberg* and Jörg Mathieua

Abstract: Non-military explosives are used mainly for mining and tunnel construction, for building demolition and for various special uses such as setting off avalanches and for seismic investigations. Common to all explosives is their heterogeneous structure, the great work capacity (blast effect) and the advantage that the detonation releas- es only small amounts of poisonous explosion gases. Modern explosives for tunnel construction can be pumped and are capable of exploding only on site, by the addition or chemical generation of microbubbles. With the intro- duction of electronic detonators, explosive technology entered a new era. These detonators are very safe and pre- cise, and it is possible to program up to 1600 detonators in one blasting operation.

Keywords: Blast effect · Detonator · Explosive plating · Explosives · Tagging

1. Introduction itary explosives, exhibit a strong propulsive oil as the combustible component. effect (work capacity or blast effect), but These cost-effective explosives have at- In contrast to military explosives, which are only a restricted ability to accelerate metals tained world-wide importance because they mostly based on uniform molecules, explo- (brisance). are easy to produce and very safe to handle, sives for non-military use are composed of even as freeflowing loose materials. Their oxidising, reducing, sensitising, and inert high sensitivity to moisture, however, due components. In order that the greatest pos- 2. Historical Development to the strongly hygroscopic behaviour of sible explosive or blast effect can be the ammonium nitrate, limits their possible achieved, and that the smallest possible The beginning of work with explosives use to dry drill-holes, which means that amounts of the poisonous explosion gases in mining, and therefore also in tunnel con- their use in tunnel construction is severely CO and NOx are created in the detonation, struction, started in 1627. In that year, the restricted. In 1956, the American Melvin A. the mixtures are mostly adjusted to a bal- miner Caspar Weindl detonated in Slovakia Cook was the first one to succeed in mak- anced to positive oxygen balance. the first documented underground explo- ing ANFO-like explosives water-resistant. Traditional explosives are made sensi- sion, using black powder. From there on, He developed an explosive mixture made tive by means of blasting oils such as glyc- the customary method of driving shafts by up of water, ammonium nitrate and alu- erol trinitrate, nitroglycol or mixtures of ‘Feuersetzen’, working with miners’ ham- minium, and used it successfully. Because these two. Explosives such as TNT are mers and iron tools, was slowly replaced. of their paste-like, granular, sludgy consis- added as well. Modern formulations are Until the second half of the 19th centu- tency, explosive mixtures of this kind are characterised by high stability during stor- ry black powder remained the only explo- referred to as ‘slurry explosives’. In 1970, age and an insensitive behaviour. They are sive used in mining and tunnel construc- simple and water-resistant nitrate explo- made capable of detonation only on site by tion. Over 200 years after black powder was sives were successfully developed in the introducing finely distributed gas bubbles. first used, the invention of DYNAMITE by USA. These are now the latest generation of Due to the heterogeneous structure of Alfred Nobel in 1865 brought a change to explosives which contain water but no in- non-military explosive formulations, a high working with explosives. Nobel succeeded herently explosive ingredients. proportion of non-ideal conversion during in making the blasting oil – better known as the detonation occurs, which does not con- glycerol trinitrate, which was actually dis- tribute to sustaining the shock front. Conse- covered 20 years earlier, safe to handle by 3. Composition of Non-military quently these explosives, in contrast to mil- absorbing it into kieselguhr. With the in- Explosives vention of this highly explosive material, the forerunner of all present-day gelatinous 3.1. Gelatinous Explosives explosives, and the introduction of drilling For over 120 years the most commonly by machine, the necessary conditions for used non-military explosives have been the *Correspondence: O. Ringgenberg modern tunnel construction were created. gelatinous explosives. They consist mainly TSSA Tunnel Service AG A patent for an explosive without blast- of a mixture of blasting oil gelatinised with Walchistrasse 30 ing oil, but based on ammonium nitrate, had nitrocellulose – so-called explosive gelatine CH–6078 Lungern Tel.: +41 41 679 77 90 already been applied for in Sweden in 1867. – and the oxidising agent ammonium ni- Fax: +41 41 679 77 95 The first ANFO (Ammonium Nitrate Fuel trate. Normally the proportion of gela- E-Mail: [email protected] Oil) explosives containing no blasting oil tinised blasting oil is between 20 and 40%. a armasuisse gained world-wide acceptance only in the With that percentage of blasting oil, these Science and Technology Feuerwerkerstrasse 39 mid 1950s. These consist solely of ammo- explosives are without exception sufficient- CH–3602 Thun nium nitrate as oxidizing agent and mineral ly sensitive to be detonated by the energy of EXPLOSIVES 391 CHIMIA 2004, 58, No. 6

Table 1. Example of an ammonium saltpetre gelatine composition the form of a ‘water-in-oil emulsion’ with the help of emulsifying agents. Similar to Components Content [%] Effect ANFO explosives and slurries of the blast- ing-agent type, they contain no components Nitroglycerine 24.5 Sensitisation classified as pure explosive materials. Until hollow microspheres or gas-forming chem- Collodion wool 1.5 Gelatinisation of the nitroglycerine. ical ingredients e.g. nitrites in combination (nitrated cellulose with The water serves to stabilise the collodion with thiourea are added, the material matrix 11% N content) + water wool of emulsion explosives is therefore inca- Ammonium nitrate 61 Oxidising agent pable of detonation. This characteristic and the insensitivity to impact and friction is not Barium sulphate 3 Flame reducing agent achieved by any other type of explosives. They are the safest commercial explosives Cellulose 4.5 Reducing agent and optimisation of in terms of handling today. Another positive mechanical properties asset is the particularly high resistance to Dinitrotoluol 5.5 Source of energy water and the only slight toxic composition of the explosive clouds in respect of CO and NOX. Emulsion explosives are manufac- a single blasting cap. Gelatinous explosives can be used only in the form of cartridges. As gelatinous explosives age, migration of the blasting oils takes place. This process is greatly accelerated by large temperature fluctuations. A shelf life of two years is therefore usually specified for gelatinous explosives. Table 1 shows an example of a gelatinous explosive composition.

3.2. Ammonium Nitrate Fuel Oil (ANFO) ANFO consists of 94% granulated porous ammonium nitrate and 6% oil as fuel. ANFO explosives are classified as so- called hard-to-detonate explosives. They can be detonated only when activated suffi- ciently by a booster charge, and are there- fore responsive to blasting caps only to a limited extent. Fig. 1 illustrates the open ex- plosive mining of lime with a mixed charge of ANFO and gelatinous explosive.

3.3. Slurry Explosives Slurry explosives are mixtures of aque- ous, inorganic salt solutions and non-solu- ble liquid and/or solid oxidisable reaction partners. Components providing oxygen are various nitrates, most commonly am- monium nitrate. Characteristic of this type of explosive is the high water content of 10–20%, in which some or all of the salts Fig. 1. Open explosive 3 which provide oxygen are present in solu- mining of 13,000 m tion. From this water content, the frequent- Jurassic lime with 4000 kg ANFO and ly used name ‘water-gel’ is derived. Two water-gel explosive. types of slurries are known. Slurry explo- Top: immediately after sives (SE), which are rendered sensitive ignition of the explo- with explosive materials, and slurry blast- sion. Middle: Devolu- ing agents (SBA), which contain no inher- tion of the explosion ently explosive materials and are sensitised with pushing the ma- by introducing a large number of very small terial without shying cavities, so-called hot spots. effect to the surround- ing area. Bottom: The 3.4. Emulsion Explosives explosion ended with a good result. The for- In general the term emulsion explosives mation of dust was is used for mixtures of high-concentration normal and the infra- salt solutions containing oxygen and com- structure remained bustible components. They are stabilised in free of damage. EXPLOSIVES 392 CHIMIA 2004, 58, No. 6 tured either in cartridges or in pumpable cient resistance in an explosion. Currently After ignition, this explosive coating deto- bulk form [1]. three products are approved in Switzerland. nates in the tube with a velocity of 2000 Of these, two provide visual coding in the m/s, so as then to ignite the delay stages of 3.5. Explosives for Underground form of several layers of paint. These parti- the incorporated time detonators. Mining cles can be evaluated visually under the mi- With the introduction of the first elec- In mining (especially coal mining), the croscope. In the third product the informa- tronic detonators to the market 15 years risk of so-called firedamp explosions is tion is present in chemical form, which ago, detonator technology reached a new high. The use of conventional explosives is makes chemical analyses necessary for de- peak. Instead of the traditional pyrotechnic therefore impossible. These atmospheric coding it. Explosive manufacturers are re- delay elements, electronic detonators con- explosions are explosions of mixtures of quired to change the code after a specified tain an integrated switching circuit in the methane (‘firedamp’) and air, or of coal quantity of explosive has been produced, or form of a microchip. Each detonator is pro- dust and air. The shock wave created in such after a maximum production period. vided with its own power supply, a capaci- events extends throughout the whole tor. In respect of the structure of the explo- gallery system. However, atmospheric ex- 4.2. Tagging of Explosives for the sive part, the electronic detonator is identi- plosions are not set off by the first spark Purpose of Detection cal to a modern instantaneous igniter. which occurs. Depending on the flame tem- As a result of the explosive attack on a Irrespective of the delay time, with this perature, ignition takes place only after a Pan Am aircraft over the town of Lockerbie, type of detonator the scatter of the delay delay of up to several seconds. At 650 °C the international agreement on the tagging time is less than half a millisecond. The this time is about 10 sec, falling to 1 sec at of plastic explosives for the purpose of de- time interval can be programmed freely for 1100 °C. In order to prevent atmospheric tection was drawn up. This has meanwhile each detonator within a range of 0 to 15,000 explosions being set off, so-called permis- been ratified by 91 states, including ms. A total of up to 1600 detonators can be sible explosives had to be developed. These Switzerland. This form of tagging is in- used in any one blasting operation [4]. are characterised by a particularly low tended as a preventive measure. With ex- flame temperature in the reaction gases. plosive-detection systems in operational With conventional gelatinous explo- use, hidden explosives are expected to be 6. Performance sives this effect is achieved by the addition detected easier. The agreement applies to of up to 40% of sodium chloride. The lat- both non-military and military explosives. In order that debris can be cleared away ter’s relatively high thermal conductivity efficiently and further use of the material and specific heat extracts energy from the produced by the blast is not restricted, the hot gas clouds, and as a result the flame 5. Detonators rock must not be broken down into exces- temperature of the reaction gases is re- sively small pieces by blasting. In mining duced. In mining and tunnel construction, and and tunnel construction, explosives are High-safety explosives are materials also in the demolition of buildings and oth- used which are highly effective in moving which contain inverse salt pairs. Instead of er structures using explosives, the success material (work capacity) but have a limited the potentially explosive ammonium ni- of the operation depends on the various se- shattering effect (brisance). The high trate, harmless ammonium chloride and ries of explosions being set off at specified propulsive blast effect of non-military ex- sodium nitrate are added to the formulation. time intervals. On one hand, the sequence plosives is based on their high explosion If the glycerol trinitrate, which is present in of the explosion is determined by the initi- heat and the large quantity of reaction gas- low concentration is detonated, its energy ation delays; on the other hand, the shock es which are released in the detonation. In remains concentrated in the drill-hole. This effect on the surrounding area can be great- comparison to military formulations, non- energy is sufficient to briefly create ammo- ly reduced. The need for explosive charges military explosives exhibit a lower detona- nium nitrate and sodium chloride again, to be set off not simultaneously, but in a tion velocity, as well as lower pressure and which then react in the well-known way. If, specified sequence which is defined as pre- temperature in the detonation front. This re- however, a neighbouring charge has already cisely as possible, has been a requirement sults in a lesser shattering effect on the im- carried away rock, so that the safety explo- placed on explosive technology from the mediate surrounding area. This behaviour is sive is freely in contact with the methane- very beginning. In earlier times, different mainly attributable to the fact that non-mil- air mixture, detonation of the glycerol trini- delays were achieved by time fuses of dif- itary explosives exhibit a markedly lower trate only hurls off the unrestrained mixture ferent lengths, or by an appropriate se- density, as well as a high proportion of non- of the inverse salt pairs, and a firedamp ex- quence in lighting them. Today – as a result ideal conversion in the detonation. Table 2 plosion can thereby be avoided. of intensive research and development – presents the performance data of a choice of highly precise electric, non-electric and commercial high explosives. electronic delayed-action ignition devices 4. Tagging [2] are available [3]. With electric detonators the time delay 7. Explosive Plating 4.1. Tagging for the Identification of is achieved by appropriate pyrotechnic de- Commercial Explosives lay elements. Until the early 1950s, only In addition to mining and tunnel con- All non-military explosives used in detonators with half-second intervals were struction, non-military explosives are also Switzerland must include a tagging compo- available. Today detonators with short time used for a large number of special applica- nent by means of which the origin and peri- intervals of 20 to 500 ms can be used, which tions, such as building demolition, setting od of manufacture can be established reli- facilitate a precise time graduation up to a off avalanches, seismic investigations, ably, even after the explosion. This is stated maximum of 6 sec. blasting of drainage channels in the oil in the ordinance issued under the Federal In non-electric detonation systems, the industry and also in metal-forming tech- Law on Dangerous Explosive Materials ignition impulse is transmitted by the deto- nology. (Explosives Ordinance), Article 18. These nation of very small amounts of an explo- A further special application is explo- tagging substances are required to provide sive in a plastic tube. To achieve this, the in- sive plating. This process enables various good detectability, simple storage, chemi- ner surface of the tube is dusted with 16 to metals to be joined which cannot be weld- cal resistance in the explosive, and suffi- 20 mg of explosive per metre tube length. ed conventionally. The resulting thin layers EXPLOSIVES 393 CHIMIA 2004, 58, No. 6

Table 2. Performance data of non-military explosives. In the lead-block test, the expansion of a de- fined cavity caused by detonation of the substance is measured.

Name Type Density Detonation Lead-block Gas volume (used as) velocity expansion test [l/kg] [m/s] [cm3/10 g]

Gamsit A gelatinous 1.40 6200 420 850 (cartridge) Gotthardit slurry 1.20 4700 – 715 100 (cartridge) Tovex S water-gel 1.30 4000 380 650 (cartridge) Emulga emulsion 0.95– 1.15a 3900–4500 cannot be max. 960 (pumped) measured: not sensitive to cap a The density can be adjusted locally, according to the nature of the rock

of the joint metals have high mechanical ergetic ‘jet’ comprised of the spalled mate- strength. For example, in the shipbuilding rials ejects metal oxides and surface debris industry, aluminium can be plated onto as the detonation front progresses. The mat- steel. With the aid of stripes of such con- ing surfaces collide under pressure of sev- necting elements, light aluminium super- eral million pounds per square inch. The structures can then be mounted on the mas- combination of surface cleaning and ex- sive steel hull by means of conventionally treme pressure produces a very thin contin- welded joints, without the use of rivets. In uous metallurgical weld [5]. the chemical industry this technology is used for the manufacture of reactor vessels Received: March 30, 2004 which are resistant to chemicals. To achieve this, thin layers of titanium are plated onto [1] W. Thum, ‘Sprengtechnik im Steinbruch steel, which serves as the base metal. und Baubetrieb’, Bauverlag, 1978, ISBN The process of explosive plating is 3-7625-0505-5. shown in Fig. 2. In preparation, the [2] Statement of K. Schlatter and J. Schärer, cladding and base metal mating surfaces Wissenschaftlicher Forschungsdienst Stadt are ground and then fixtured parallel at a Zürich, 2004. precise spacing. A measured quantity of a [3] O. Ringgenberg, A. Egger, ‘Felstechnik’, specifically formulated explosive is placed sprengtechnisches Handbuch für den on the cladding metal surface. The detona- Praktiker, Gasser Felstechnik AG, 2003. [4] J. Petzold, F. Hammelmann, Orica Ger- tion front travels uniformly across the sur- many GmbH, Troisdorf. Nobel Heft face from initiation. The cladding metal be- 1/2000. neath the detonating explosive is propelled [5] www.dynamicmaterials.com/clad/ to collide with the base metal at a specific detaclad.htm impact velocity and angle. The resulting momentum exchange causes a thin layer of material to be spalled from the mating sur- faces preceding the collision point. An en-

Fig. 2. The DETACLAD® process creates a high-strength, ductile, metallurgical weld