Explosion prevention methods

Methods 1 and 2 prevent combustion at a rate sufficient to result in an explosion methods 3 and 4 are listed as protection methods based on limiting or preventing damage. Spark extinguishing is also listed as an explosion prevention method by NFPA69 (2000) but is only applicable to ducts transporting combustible dusts and must be used in conjunction with one of the other explosion prevention methods or explosion venting for protection of the complete system. 

Fire and Explosion Prevention. Prevention of fire and explosion takes place in the design of chemical plants. Such prevention involves the study of material characteristics, such as those in Table 1, and processing conditions to determine appropriate ha2ard avoidance methods. Engineering techniques are available for preventing fires and explosions. Containment of flammable and combustible materials and control of processes which could develop high pressures are also important aspects of fire and explosion prevention. 

Maximum Pressure and Rate of Pressure Rise and KJ These explosibility parameters are used in assessing whether equipment will contain the maximum pressure developed during deflagration, or to design deflagration relief vents and other explosion prevention systems (see NEPA 68 and 69). The test method is given in ASTM E 1226. 

Explosion suppression can be a very elegant method to prevent dust explosions. This method utilizes the fester propagation of the pressure wave in comparison to the flame fix>nt. The vessel to be protected is equipped with containers comparable in size and design to fire extinguishers. They are filled with a substance which suffocates the fire in a comparable way to powder extinguishers. 

The process factor is associated with the characterization of material being dried and the physical conditions to which it is subjected. This is a very important consideration because it enables for the recognition and assessment of fire and explosion hazards. For this factor, the basis of safety is the prevention methods (e.g., drying in an inert atmosphere, elimination of the formation of explosive mixtures, and rigorous exclusion of all possible ignition sources). 

It is to be noted that there is no need to duplicate any method of protection or prevention. Methods of dust explosion prevention and protection are described in three Institute of Chemical Engineers (IChemE) gnides [30-32] and in Refs. [33] and [34]. 

For materials undergoing exothermic oxidation, the methods given below will be satisfactory for explosion prevention, whereas for materials undergoing exothermic decomposition resulting in the release of large volumes of gases, these methods can be used only to protect, not to prevent, explosion hazards. 

The two main methods of explosion hazard control are explosion prevention (e.g. preventing formation of explosible dust clouds, removing all possible ignition sources, creating an atmosphere that cannot support combustion) and explosion protection (e.g. venting, suppression, containment and/or isolation). Quite often it is difficult to guarantee explosion prevention (e.g. due to equipment/instrumentation failure and/or human error). Explosion protection usually is pursued to protect personnel and minimise plant damage. Despite the similarities with gas explosions, dust explosions can be quite different ... 

The latter method typically requires less severe conditions than the former because of the labile nature of the organic anhydride (87,137). Both of these reactions can result in explosions and significant precautions should be taken prior to any attempted synthesis of a peracid (87). For soHd peracids the reaction mixture can be neutralized with sodium hydroxide and the resulting fUtercake washed with water. In the case of the sulfuric acid mediated reaction the peracid has sodium sulfate incorporated in the cake (135). The water of hydration present in the sodium sulfate is desirable to prevent detonation or deflagration of the soHd peracid when isolated in a dry state (87,138,139). 

Bv this method, in general, the expecl ed inherent maximum explosion overpressure of the order P = 7 to 10 bar will be reduced to a value of Pred.max < 2 bai. In this case, the static activation overpressure of the venting device is < 0.1 bar. The resulting P,ed,max i i y not exceed the design pressure of the equipment. The explosion as such is not prevented only the dangerous consequences are limited. However, subsequent fires must be expecl ed. 

In 1854, the Manchester Steam Users Association was formed to help with the prevention of explosions in steam boilers and to find efficient methods in their use. To achieve this, the Association employed the first boiler inspectors, whose services were then made available to the Association s members. Within a short space of time, the members became convinced that insurance to cover the high cost of repair or replacement of damaged boilers was desirable, and this resulted in the first boiler insurance company (The Steam Boiler Assurance Company) being formed in 1858. The scope of the services for inspection and insurance later extended to include pressure vessels, steam engines, cranes, lifts and electrical plant, the insurance protection in each case being supported by an inspection service carried out by qualified engineer surveyors. 

The present procedure is substantially simpler and quicker than the best previous procedure,3 which requires 4 days instead of 4 hours. It is also safer, for no explosions have been encountered with the present procedure, even on a 1.2-mole scale,3 whereas care must be taken to prevent explosion of the intermediate hypobromite when the Hunsdiecker method is used,3 and one detonation has been reported. In comparison with the peroxide method,4 it is simpler and gives better yields. 

Davy, H., On the fire-damp of coal mines and the methods of lighting the mines so as to prevent explosions, Phil. Trans. Roy. Soc., 106 1,1816. 

Olah, G. A. et al., J. Inorg. Nucl. Chem., 1960, 14, 295-296 Experimental directions must be followed exactly to prevent violent spontaneous explosions during preparation of the salt from silver oxide and boron trifluoride etherate in nitromethane, according to the earlier method [1], The later method [3] is generally safer than that in [2],... 

The material is impact-sensitive when dry and is supplied and stored damp with ethanol. It is used as a saturated solution and it is important to prevent total evaporation, or the slow growth of large crystals which may become dried and shock-sensitive. Lead drains must not be used, to avoid formation of the detonator, lead azide. Exposure to acid conditions may generate explosive hydrazoic acid [1], It has been stated that barium azide is relatively insensitive to impact but highly sensitive to friction [2], Strontium, and particularly calcium azides show much more marked explosive properties than barium azide. The explosive properties appear to be closely associated with the method of formation of the azide [3], Factors which affect the sensitivity of the azide include surface area, solvent used and ageing. Presence of barium metal, sodium or iron ions as impurities increases the sensitivity [4], Though not an endothermic compound (AH°f —22.17 kJ/mol, 0.1 kj/g), it may thermally decompose to barium nitride, rather than to the elements, when a considerable exotherm is produced (98.74 kJ/mol, 0.45 kJ/g of azide) [5]. 

It is fairly stable as an ethereal solution, but the isolated acid is explosively unstable, and sensitive to heat, shock or friction [1], In a new method of preparation of the acid or its salts, pyrolysis of 4-oximato-3-substituted-isoxazol-5(4//)-ones or their metal salts must be conducted with extreme care under high vacuum to prevent explosive decomposition [2],... 

Caution is advised [1] to prevent explosions when using an analytical method involving sequential addition of acetic acid, aqueous 4-toluenesulfonic acid and acetic anhydride to serum [2], It is difficult to see why this should happen, unless the anhydride were all added before the sulfonic acid solution. 

Dining interaction at ambient temperature in a bomb to produce poly (carbon monofluoride), admission of fluorine beyond a pressure of 13.6 bar must be extremely slow and carefully controlled to avoid a violently exothermic explosion [1], Previously it had been shown that explosive interaction of carbon and fluorine was due to the formation and decomposition of the graphite intercalation compound, poly (carbon monofluoride) [2], Presence of mercury compounds prevents explosion during interaction of charcoal and fluorine [3], Reaction of surplus fluorine with graphite or carbon pellets was formerly used as a disposal method, but is no longer recommended. Violent reactions observed when an exhausted trap was opened usually involved external impact on the metal trap, prodding the trap contents to empty the trap, or possibly ingress of moist air... 

In a new method for determination of sulfur in coal, the samples are oxidised with an aqueous mixture of permanganate and the peroxoacid. During the digestion, a reflux condenser is essential to prevent loss of water, which could lead to explosively violent oxidation. 

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