Dusting, air

When dispersed as a dust, adipic acid is subject to normal dust explosion hazards. See Table 3 for ignition properties of such dust—air mixtures. The material is an irritant, especially upon contact with the mucous membranes. Thus protective goggles or face shields should be worn when handling the material. Prolonged contact with the skin should also be avoided. Eye wash fountains, showers, and washing faciUties should be provided in work areas. However, MSDS Sheet400 (5) reports that no acute or chronic effects have been observed. 

For example, in rotary vacuum dryers it is possible to prevent the formation of explosible dust-air mixtures by setting and monitoring a certain partial vacuum (negative pressure). This pressure value must be determined by experiment for each type of dust. With pressures of less than O.I bar, in general, hazardous effects of dust explosions need not be anticipated. If the vacuum system malfunctions, the partial vacuum must be released by inert gas and the instaUation shut down. 

Sparks Discharge Spark discharges can ignite dust-air mixtures up to an MIE of 1 J. If an uncertainty area is taken into account, this corresponds to an EIE of I to 10 J. 

Propagating Brush Discharge The incendivity of the propagating brush discharge is so large that an ignition of dust-air mixtures with an MIE up to around 100 J must be anticipated. For dust-air mixtures, this corresponds to an EIE range of 10 to 100 J. 

FIQURE 6-1.3.1. Hypothetical effect of adding ether to different dust-air mixtures. 

Ignition of a flammable dust-air mixture is more difficult than with flammable vapour-air mixtures. A larger source of heat is required, and a larger volume of fuel must be heated to the ignition point. The same range of potential ignition sources is applicable as for air-vapour mixtures. 

The dimensionless ratio R is the ratio of the maximum deflagration pressure, in absolute pressure units, to the maximum initial pressure, in consistent absolute pressure units. For gas/air mixtures, R shall be taken as 9.0 for dust/air mixtures, R shall be taken as 10.0. 

Bruderer, R. E., Ignition Properdes of Mechanical Sparks and Hot Surfaces in Dust-Air Mixtures, Ibid., p. 152. 

Barlknechi, W., Ignidon Capabilides of Hot Surfaces and Mechanically Generated Sparks in Rlammable Gas and Dust/Air Mixtures, FZfflMi/Ojberfflfaon.f Prog-., V. 7, No. 2, 1988, p. 114. 

Increasing the surface area of a combustible solid enhances the ease of ignition. Solid particles less than about 10 pm in diameter settle slowly in air and comprise float dust . Such particles behave, in some ways, similarly to gas and, if the solid is combustible, a flammable dust—air mixture containing a distribution of particle sizes can form within certain limits. 

Ignition of a flammable dust—air mixture is more difficult than with air—vapour... 

A. Fox. R. M. T. Rosario, and L. Larsson, Monitoring of bacterial sugars and hydroxy fatty-acids in dust air-conditioners by gas-chromatography mass-spectrometry, Appl. Environ. Microbiol. 59 4360 (1993). 

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

Maximum reduced explosion overpressure PreThe maximum pressure generated by an explosion of a dust-air mixture in a vented or suppressed vessel under systematically varied dust concentrations. 

Combustible dust-air mixtures These mixtures can be avoided or restricted if the combustible dust can be replaced by a noncombustible dust or the dust concentration can be kept so low that an explosive dust-air mixture is never actually formed. 

Combustible dust-air mixtures For every installation a check has to be made to determine which ignition source may become effective and whether it can be prevented with a sufficient degree of safety. With more sensitive products and complex installations, it becomes more and more difficult to exclude ignition sources with ample safety. 

The following empirical equations, Eqs. (23-15) to (23-17), allow the calculation of the size of a vent area A for combustible dust-air-... 

Table VI compares results from air, dust and slurry investigations on VFA and phenolic/indolic compounds in piggeries. Relative values are used. When comparing the results derived from investigations on dust, air or slurry it is necessary to use relative values because of the different dimensions, for experience shows that in spite of large quantitative differences between two samples within the group of carboxylic acids and within the group of phenolic/indolic compounds the proportions of the components remain rather stable (36). In the group of VFA acetic acid is the main component in air, dust, and slurry followed by propionic and butyric acid. The other three acids amount to less than 25%. In the group of phenols/ indoles p-cresol is the main component in the four cited investigations. However, it seems that straw bedding can reduce the p-cresol content in this case phenol is the main component, instead (37).

Theoretical investigations of the problem were carried out on the base of the mathematical model, combining both deterministic and stochastic approaches to turbulent combustion of organic dust-air mixtures modeling. To simulate the gas-phase flow, the k-e model is used with account of mass, momentum, and energy fluxes from the particles phase. The equations of motion for particles take into account random turbulent pulsations in the gas flow. The mean characteristics of those pulsations and the probability distribution functions are determined with the help of solutions obtained within the frame of the k-e model. 

The dust-air mixture was ignited in the center of the site by the energy release in a ball-shape volume. 

Smirnov, N.N., V. F. Nikitin, J. Klammer, R. Klemens, P. Wolanski, and J. C. Legros. 1996. Dust-air mixtures evolution and combustion in confined and turbulent flows. 7th Colloquium (International) on Dust Explosions Proceedings. Bergen, Norway. 552-66. 

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