Gases maximum explosion pressure

Tlie maximum explosion pressure is a function of the initial pressure, P. If tlie initial pressure is increased by a factor of 2, tlie maximum explosion pressure and the maximum pressure rise will also increase by a factor of about 2 for both naminable gas and dust mixtures. Wlien tlie initial pressure is less tlian 10 mbar, il is usually no longer possible to Iwve an explosion. 

The maximum explosion pressure is a function of and is directly proportioiuil to die initial pressure. Blast waves are pressure waves of finite amplitude tliat are generated in air by a rapid release in energy and an instantaneous rise in pressure. The most conunon plant explosion types eiicomitered in iiidustiy are chemical, nuclear, expanding vapors, and pressurized gas. 

This is valid for the same degree of gas mixture turbulence and the same ignition source and is illustrated in Figure 7-58. Influence of the vessel shape is shown in Figure 7-56. The behavior of propane is considered representative of most flammable vapors including many solvents [54]. The maximum explosion pressure does not follow the cubic law and is almost independent of the volume of a vessel greater than 1 liter. For propane, town gas, and hydrogen, the volume relationship can be expressed ... 

FPN No. 2) The explosion characteristics of air mixtures of gases or vapors vary with the specific material involved. For Class I locations. Groups A, B, C, and D, the classification involves determinations of maximum explosion pressure and maximum safe clearance between parts of a clamped joint in an enclosure. It is necessary, therefore, that equipment be approved not only for class but also for the specific group of the gas or vapor that will be present. 

Finely powdered silicon can give significant dust explosion hazards. Relationships of sensitivity to spark ignition and of explosibility to particle size are studied [1]. Maximum explosion pressures of 6.4 bar, with maximum rate of rise of 884 bar/s have been determined [2], Silicon dust is likely to result from processes using silanes in the gas phase [3],... 

Flammability limits for vapors are determined experimentally in a specially designed closed vessel apparatus (see Figure 6-14 on page 255). Vapor-air mixtures of known concentration are added and then ignited. The maximum explosion pressure is measured. This test is repeated with different concentrations to establish the range of flammability for the specific gas. Figure 6-5 shows the results for methane. 

Initial pressure affects maximum explosion pressure and rate of pressure rise. If the initial pressure is increased above atmospheric pressure, there will be a proportional increase in the maximum explosion pressure and in the rate of pressure rise. Reducing the initial pressure will cause a corresponding decrease in maximum explosion pressure until finally an explosion reaction can no longer be propagated through the gas mixture. 

The maximum pressure is derived from the ideal gas equation. The original gas, at 1 atm. and 298 K, consisted of iHa, Oaand 2Na, whereas the final gas at 2920 K consists of IH2O and 2Na. Since PV = nRT, with V and B constant, it is easily shown that the maximum explosion pressure is... 

An explosion pressure, is the pressure in excess of the initial pressure at which the explosive mixture is ignited. The rate of pressure rise is represented by dP/dt. This is the change in pressure with respect to time. The rate of pressure rise is a measure of the speed of the flame propagation therefore, it is also a measure of the violence of the explosion. Typical values of maximum explosion pressures in a closed vessel range from 7 to 8 bar. The rate of pressure rise can vary considerably with the flammable gas. The influence of vessel volume on the maximum rate of pressure rise for a given flammable gas is characterized by the cubic law ... 

The temperature rise and the possible increase in gas molecules as a result of combustion causes the pressure in a closed vessel to rise. The violence of a gas explosion can be expressed by the maximum explosion pressure, Pmax. and the maximum rate of pressure rise, (dP/dt)max. measured in a closed test vessel. " The product of the maximum rate of pressure rise and the cubic root of vessel volume ... 

Containment means to construct a vessel or equipment to withstand the maximum explosion pressure resulting from gas explosions. The following points should be considered ... 

Brisance is the destructive fragmentation effect of a charge on its immediate vicinity. The relevant parameters are the detonation rate and the loading density (compactness) of the explosive, as well as the gas yield and the heat of explosion. Brisance is a measure for the time required to build up the maximum explosion pressure. 

Chapter I, Vapor Cloud Explosions, presents recent research on the safety hazards and explosion damage potential associated with the accidental release of combustible vapor clouds. Stock et al. report on experiments with explosive clouds formed by turbulent jets of propane, natural gas, or hydrogen released through various-sized orifices. They found significant scale effects, e.g., the maximum explosion pressure increased with the size of the vapor cloud and with the turbulence level in the jet. Desrosiet and coworkers have experimented with asymmetric explosions of vapoi clouds. They present results on how the ignition asymmetry of a hemi-... 

Excessive temperature can lead to premature failure of an item of equipment at pressures below its design maximum working pressure. Such a failure can create a leak, potentially leading to fire or explosion if gas is leaked or to oil pollution if oil is leaked. This type of failure should be gradual, with warning as it develops, and thus does not require as higli a degree of protection as those previously mentioned. 

The pressure of explosion Pe is the maximum static pressure which may be achieved when a given weight of explosive is burned in a closed vessel of fixed volume. The pressure attained is so high that the Ideal Gas Laws are not sufficiently accurate and have to be modified by using a co-volume a. At high pressure... 

Problem A mixture of hydrogen gas and the theoretical amount of air, at 25 C and a total pressure of 1 atm., is exploded in a closed vessel. Estimate the maximum explosion temperature and pressure, assuming adiabatic conditions. In order to simplify the calculation, the mean heat capacities of nitrogen (8.3 cal. deg. " mole " ) and of water vapor (11.3 cal. deg. " mole" ), for the temperature range from 25 to 3000 C, may be used they may be regarded as independent of the (moderate) pressure. 

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