Deflagration, described

Prior to reading this subject, it is advisable to see "Burning (Combustion) and Deflagration of Gases, Vapors and Dusts Detonation and Explosion of Dusts and Mists (Vapors) and Detonation (or Explosion), Development (Transition) from Burning (Combustion) or Deflagration described in this Volume... 

This book covers many aspects of DBA design, selection, specification, installadon, and maintenance. It explains how varions types of flame arresters differ, how they are constrncted, and how they work, ft also describes when a flame arrester is an effective solntion for mitigation of deflagrations and detonations, and other means of protection (e.g., oxidant concentration rednction) that may be nsed. It also briefly covers some aspects of dnst deflagration protection. 

Fabiano et al. (1999) describe an explosion in the loading section of an Italian acetylene production plant in which the installed flame arresters did not stop a detonation. The arresters were deflagration type and the arrester elements were vessels packed with silica gel and aluminum plates (Fabiano 1999). It was concluded that the flame arresters used were not suitable for dealing safely with the excess pressures resulting from an acetylene decomposition, and may not have been in the proper location to stop the detonation. 

Nichols (1999) describes a nnmber of reaction forces that are generated dnring deflagrations and detonations in piping systems snch as ... 

This volume consists of two parts Chapters 1-6 and Chapters 7-9. Chapters 1 through 6 offer detailed background information. They describe pertinent phenomena, give an overview of past experimental and theoretical research, and provide methods for estimating consequences. Chapter 2 describes the phenomena covered, identifies various accident scenarios leading to each of the events, and describes actual accidents. In Chapter 3, principles such as dispersion, deflagration, detonation, blast, and radiation are explained. 

This chapter describes the main features of vapor cloud explosions, flash fires, and BLEVEs. It identifies the similarities and differences among them. Effects described are supported by several case histories. Chapter 3 will present details of dispersion, deflagration, detonation, ignition, blast, and radiation. 

A deflagration can best be described as a combustion mode in which the propagation rate is dominated by both molecular and turbulent transport processes. In the absence of turbulence (i.e., under laminar or near-laminar conditions), flame speeds for normal hydrocarbons are in the order of 5 to 30 meters per second. Such speeds are too low to produce any significant blast overpressure. Thus, under near-laminar-flow conditions, the vapor cloud will merely bum, and the event would simply be described as a large fiash fire. Therefore, turbulence is always present in vapor cloud explosions. Research tests have shown that turbulence will significantly enhance the combustion rate in defiagrations. 

The preceding section described the state of transition expected in a deflagration process when the mixture in front of the flame is sufficiently preconditioned by a combination of compression effects and local quenching by turbulent mixing. However, additional factors determine whether the onset of detonation can actually occur and whether the onset of detonation will be followed by a self-sustaining detonation wave. 

A much more pronounced vortex formation in expanding combustion products was found by Rosenblatt and Hassig (1986), who employed the DICE code to simulate deflagrative combustion of a large, cylindrical, natural gas-air cloud. DICE is a Eulerian code which solves the dynamic equations of motion using an implicit difference scheme. Its principles are analogous to the ICE code described by Harlow and Amsden (1971). 

Pj = the maximum initial pressure at which the combustible atmosphere exists, psig R = the ratio of the maximum deflagration pressure to the maximum initial pressure, as described in Code Par 5-3.3.1... 

In 1957, a flame propagating in a long tube under conditions resulting in a deflagration to detonation transition (DDT) was given the name "tulip" by Salamandra et al. [7]. This term was subsequently commonly applied in detonation studies to describe this typical shape [8,9]. Figure 5.3.2 shows a few... 

In Chapter 8.4, A. Teodorczyk presents the complex problem of transition from deflagration to detonation (DDT). He reviews the phenomena associated with the DDT process in smooth tubes according to the classical scheme and then describes DDT in obstructed channels. 

Deflagration A melting point test has been described for diazo compounds. The first 1 mm of a melting-point tube filled with c. 10 mg of test compound is inserted in a melting-point apparatus heated at 270°C. Once decomposition starts, the tube is removed. The decomposition rapidly propagates through the entire mass for unstable diazo compounds no such propagation is reported for stable versions. 

When epichlorohydrin was in the presence of trichloroethylene with chloride ion traces, there was a deflagration. Similar accidents have been described with other epoxidic substances. 

Deflagration A melting point test has been described for diazo compounds. The first 1 mm of a... 

More stable than its lower homologues, it merely deflagrates on heating. Higher homologues appear to be still more stable [1], Safe procedures (on the basis of detonability experiments) for preparation of anhydrous solutions of peroxypropionic acid in chloroform or ethyl propionate have been described [2],... 

When designing reliefs for gas or dust explosions, special deflagration data for the scenario conditions are required. These data are acquired with the apparatus already described in section 6-13. 

The results of a number of tests such as those described in Chapter 2 led to classifications for the peroxide group. These tests included the determination of the hazards of decomposition (deflagration and detonation), bum rate, fire hazard, and reactivity hazards. Five different classes were formulated, as listed in the NFPA 43B Hazard Class, from the test results. Emergency procedures have been established for these five classes. 

Thermodynamic cycles are a useful way to understand energy release mechanisms. Detonation can be thought of as a cycle that transforms the unreacted explosive into stable product molecules at the Chapman-Jouguet (C-J) state,15 which is simply described as the slowest steady-state shock state that conserves mass, momentum, and energy (see Figure 1). Similarly, the deflagration of a propellant converts the unreacted material into product molecules at constant enthalpy and pressure. The nature of the C-J state and other special thermodynamic states important to energetic materials is determined by the equation of state of the stable detonation products. 

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