Explosives stemming

Explosion finely dispersed particles form explosive mixtures on contact with air. keep dust from accumulating, closed stem, explosion-proof efectrical equ xnent and lighting, prevent buidup of electrostatic charges by grounding, etc. ... 

Stanley Grossel/ President, Proce.ss Safety h- Design, Inc. Fellow, American Institute of Chemical Engineers Member, American Chemical Society Member, The Combustion Institute Member, Explosion Protection Sy.stems Committee ofNFPA. (Emergency Relief Device Effluent Collection and Handling)... 

It is unfortunately true to say that the views which most people hold on explosives stem either from first-hand experience of the effects of explosives used during times of war, or from reports of these effects. For military purposes explosives are required to cause destruction and are used in quantities so large or in such a fashion that destruction is inevitable. As a result, the impression is given of an overwhelming force causing uncontrolled devastation. 

It was early recognised that an explosive is more hazardous in a coal mine if it is fired in a borehole from which the stemming is omitted or blown out early by the explosive than if it is fired in a properly stemmed hole and does adequate work in bringing down rock or coal. The tests which led to the original permitted explosives, now called P1 explosives, were therefore designed to test the product under these conditions. 

Five shots are fired of 795 g explosive with direct initiation, stemmed into methane/air mixture. No ignitions may occur. 

Figure 14.10 illustrates the method of seismic prospecting on land by what is known as reflection shooting. A hole usually 10 to 12 cm in diameter is drilled to a depth of 15 to 30 m. The charge of explosive is likely to be 5 to 12-5 kg and the stemming used is usually water. As the explosive must fire under a depth of water which may exceed 45 m, special varieties of gelatines are employed (see p. 53). Alternatively, a powder explosive can be sealed into pressure-resistant metal containers. Special detonators are also employed, not only to withstand the possible head of water, but also to have a specially short bursting time (see p. 113). 

Stemming. The insertion, into the end of a borehole, of clay or other material which will resist the pressure of the explosive when the latter is fired. 

Though relatively stable,explosions have been caused by distillation to dryness [1], or attempted distillation at ambient pressure [2]. In a comprehensive review of the use of the hydroperoxide as a selective metal-catalysed oxygenator for alkenes and alkynes, attention is drawn to several potential hazards in this application. One specific hazard to be avoided stems from the fact that Lucidol TBHP-70 contains 19% of di-ferf-butyl peroxide which will survive the catalysed reaction and may lead to problems in the work-up and distillation [3], A thorough investigation of the stability and explosive properties of the 70% solution in water has been carried out [4]. The anhydrous peroxide as a solution in toluene may now readily be prepared azeotropically, and the solutions are stable in storage at ambient temperature. This solution is now a preferred method for using the anhydrous hydroperoxide [5],... 

Preliminaries. The combustion of suspended dusts and powders is quite complex and only imperfectly understood. The complexity stems from both fundamental and practical considerations. On the fundamental side, the ignition of suspensions of finely divided solids is influenced by hard-to-quantify factors such as the time-varying concentration of solids, the chemical activity and morphology of the particulate, and the degree of confinement provided by the vessel. On the practical side, industrial conditions are seldom sufficiently well-controlled or characterized to justify application of existing theoretical models. For all the above reasons, this chapter can provide only a very abbreviated coverage of ignition basics. The reader is referred to other sources for in-depth treatment of dust and powder explosions (Bodurtha, 1980 Bartknecht, 1981 Bartknecht, 1987). 

Accident Mitigation 28 Detection of leaks/ruptures 29 Emergency shutdown switch locations 30 Accessibility of isolation valves 31 Potential for fire/explosion in unit affecting other equipment 32 Critical controls, mitigation, communication, and fire protection sy stems functional and accessible after initial explosion or release 33 Back-up power supply/redundant feeds for critical electrical systems 34 Water supply for fire fighting 35 Routing of utilities... 

A worker walking across a high walkway in a process plant stumbles and falls toward the edge. To prevent the fall, he grabs a nearby valve stem. Unfortunately, the valve stem shears off and flammable liquid begins to spew out. A cloud of flammable vapor rapidly forms and is ignited by a nearby truck. The explosion and fire quickly spread to nearby equipment. The resulting fire lasts for six days until all flammable materials in the plant are consumed, and the plant is completely destroyed. 

Gulf of Mexico, South Marsh Island, Block 281, Platform C, Blowout, Explosion/Fire Unable to close drill stem safety valve or stand pipe valve, relief valve on mud pump released gas. 

Assuming the argument is valid, it would then be possible to contact fused NaCl (or, presumably NaOH, Na2S, or smelts with these constituents) with water and to state that the resulting explosion stemmed from a homogeneous nucleation of a solution of salt in water. Their hypothesis therefore explains qualitatively the effect of variations in smelt composition on explosivity. It also clarifies the result that green liquor normally explodes more violently than pure water since, in the former, there are dissolved salts (of the NaCl type) to enhance the salt effect at the interface. 

In the first set of experiments, the water vessels had rusted bottoms. Of the 21 tests, 14 produced explosions, but no correlation of explosion probability could be deduced. It was reported that, in all tests, molten aluminum reached the bottom of the vessel. High-speed movies showed that the entire explosion sequence between the first visible disturbance in the system to a full-scale chemical reaction was very rapid (on the order of 600 /Ltsec). Note that the word chemical was used in the quote. Lemmon suggests that chemical reactions play a key role in the explosion phenomenon, particularly for violent incidents. The proof that chemical reactions are important stems from the finding that strong explosions produced light and, also, limited spectrographic data indicated local temperatures in excess of 3000 K. The emphasis on chemical reactions was not stressed in the work of other investigators. 

In addition to erythrocytes, blood contains white blood cells, called leukocytes, of several types, and platelets, also called thrombocytes, which control blood clotting. Hematopoiesis (from the Greek, haimo, for blood, and poiein for to make ) is the process by which the elements of the blood are formed. The marrow of bone contains so-called stem cells which are immature predecessors of these three types of blood cells. Chemicals that are toxic to bone marrow can lead to anemia (decreased levels of erythrocytes), leukopenia (decreased numbers of leukocytes), or thrombocytopenia. Pancytopenia, a severe form of poisoning, refers to the reduction in circulatory levels of all three elements of the blood. One or more of these conditions can result from sufficiently intense exposure to chemicals such as benzene, arsenic, the explosive trinitrotoluene (TNT), gold, certain drugs, and ionizing radiation. Health consequences can range... 

Fickett in "Detonation Properties of Condensed Explosives Calculated with an Equation of State Based on Intermolecular Potentials , Los Alamos Scientific Lab Rept LA-2712 (1962), pp 34-38, discusses perturbation theories as applied to a system of deton products consisting of two phases one, solid carbon in some form, and the other, a fluid mixt of the remaining product species. He divides these theories into two classes conformal solution theory, and what he chooses to call n-fluid theory. Both theories stem from a common approach, namely, perturbation from a pure fluid whose props are assumed known. They differ mainly in the choice of expansion variables. The conformal solution method begins with the assumption that all of the intermolecular interaction potentials have the same functional form. To obtain the equation of state of the mixt, some reference fluid obeying a common reduced equation of state is chosen, and the mixt partition function is expanded about that of the reference fluid... 

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