Deflagration Hazards

Propagation of a combustion reaction can result in detonation or deflagration. A deflagration, with its lower flame speed, is the lesser hazard. These reactions can occur in any flammable medium, including dusts, and can be prevented or mitigated by techniques mentioned elsewhere in this volume and spelled out in the extensive NFPA publications and the loss-control literature (16,17]. 

With certain materials, a locally initiated decomposition can propagate spontaneously to a deflagration even in the absence of oxygen. These materials include a number of fine, dry powders. This section deals with such hazards. Important points to note are  

Materials to be dried or groxmd should be tested for deflagratabUity. Suppliers MSDSs or standard references will contain this information when tests have already been made. Materials especially likely to deflagrate include diazo compounds, aromatics with nitro groups, and heterocycUcs containing oxygen. 

Deflagration hazards can be controlled in many different ways. These can be classified into three groups  

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Benzoyl peroxide as a pure solid is classified as a deflagration hazard. When it is a solid containing about 30% water it is an intermediate fire hazard. As a paste (50% peroxide) it is a low fire or negligible hazard. See reference 18 for a definition of hazard classifications. Benzoyl peroxide containing 50% water will be purchased. It should be stored in a separate cool area, since all peroxides have short half-lives. 

Mixtures of stoichiometric proportions (zero oxygen balance) are a high deflagration hazard and show remarkable pressure increase effects on ignition [1], as well as lowest ignition temperatures by ARC [2],... 

The first aim of a thermal stability screening test (e.g., DSC/DTA) is to obtain data on the potential for exothermic decomposition and on the enthalpy of decomposition (AHd). These data, together with the initial theoretical hazard evaluation, are used in reviewing the energetic properties of the substance (Box 4) and the detonation and deflagration hazards of the substance (Boxes 7 and 8). The screening tests also provide data on the thermal stability of the substance or mixture, on the runaway potential, on the oxidation properties, and to a lesser extent, on the kinetics of the reaction (Box 10). 

Work on the deflagration hazards of organic peroxides has been done using a revised Time-Pressure test, to determine the characteristics of ignition sensitivity and violence of deflagration. Some correlation is evident between these characteristics and the AO content within each structurally based peroxide type. Also, for the same AO content, the nature of the characteristics appears to decrease hi the order diacyl peroxides, peroxyesters, dialkyl peroxides, alkylhydroperoxides [18],... 

The differences noted in deflagration hazards as a function of the methods of ignition (either by a fuse head or by a Nichrome wire heater) have been examined and are shown in Table 3.29. No noticable difference in the rate of pressure increase due to deflagration was obserbed for either of the methods of ignition. No effect in the assessment of deflagration hazard was observed when polyvinylidene films were used for wrapping the igniters and the samples. 

The proposed improved time/pressure test is conducted under closed conditions and assesses the deflagration hazard from the rate of pressure increase observed 81 8 3). It is, however, important to know in advance the differences between that and other... 

The purpose of the test is to determine the detonation or deflagration hazards of solid materials with combustible materials. A mixture of the test sample and a combustible material is put into the steel tube and ignited. The extent of cracking of the steel tube is observed. 

Combustible dust is a combustible particulate sohd that presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations, regard-... 

OSHA defines combustible dust as a solid material composed of distinct particles or pieces, regardless of size, shape or chemical composition that present a fire or deflagration hazard (the process that produces the explosion). When these particles are suspended in the air or some other oxidizing medium over a range of concentrations, an explosion can occur. These types of dusts include, but are not limited to, metal dust and organic dust (sugar, flour, paper, soap and dried blood), as well as dusts from certain textiles. 

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