Ashok G. Dastidar

Factors influencing the suppression of coal dust explosions

Abstract Laboratory-scale experiments were conducted to examine the influences of ignition energy, coal dust concentration and particle size of rock dust on suppression of coal dust explosions in a Siwek 20 L spherical explosion chamber. The amount of rock dust required to inert an explosion increased as the ignition energy used to initiate the explosion was increased. Excessively high amounts of rock dust were required when using high ignition energies. This is due to a phenomenon known as overdriving the explosion. Comparison of these results with those of other researchers showed that 5 and 2.5 kJ ignition sources give inerting levels similar to those obtained in mine-scale experiments and in the US Bureau of Mines 20 L chamber, respectively. Results showed that tests with an ignition source > 5 kJ may overestimate the amount of rock dust required to inert an explosion. The amount of rock dust required decreased as coal dust concentration increased beyond that required to produce a stoichiometric volatiles-air mixture. The experimental results also showed that as its particle size decreases, less rock dust is required to inert an explosion. Pocahontas and Pittsburgh coal dusts had similar inerting levels even though Pocahontas has a lower volatile matter than Pittsburgh. This can be attributed to experimental conditions in the 20 L. Siwek chamber, which drive off more volatile matter from the coal than in the standard proximate analysis test.

Evaluation of dust and hybrid mixture explosion potential in process plants

Dust explosions are a serious hazard in the process industries. They have resulted in the destruction of process plants and equipment, injury to workers, and loss of production. The five factors required for a dust explosion are: (1) fuel, (2) oxidant, (3) confinement, (4) dispersion, and (5) ignition source. These factors are often embodied in an “explosion pentagon.” Disruption of any one of these factors can prevent a dust explosion from occurring. Before mitigation of a dust explosion can take place, one has to realize the full extent of the explosion potential of the dust/powder material in the intended process environment. This can be achieved by focusing on the many ways that these five components can come together in a specific process condition to form a pentagon.

Influence of liquid and vapourized solvents on explosibility of pharmaceutical excipient dusts

Hybrid mixtures of a combustible dust and flammable gas are found in many industrial processes. Such fuel systems are often encountered in the pharmaceutical industry when excipient (nonpharmaceutically active ingredient) powders undergo transfer in either a dry or solvent prewetted state into an environment possibly containing a flammable gas.

ASTM E2931: A new standard for the limiting oxygen concentration of combustible dusts

The National Fire Protection Agency (NFPA) has a standard on explosion protection systems, NFPA 69, which provides guidelines on effective inerting to prevent explosions. The standard specifies that for inerting to be effective the oxygen concentration must be kept below the Limiting Oxygen Concentration (LOC). It then goes on to specify that the ASTM International standard E2079 be used to establish the LOC. The shortcoming of this approach is that ASTM E2079 only applies to combustible gases and vapors and not combustible dusts. As a result of this deficiency ASTM International has just introduced a new standard, ASTM E2931, Standard Test Method for Limiting Oxygen (Oxidant) Concentration of Combustible Dust Clouds. This paper discusses the nuances of this standard and compares experimental results between the 20‐L chamber and the 1‐m3 chamber. Differences in the test results between the vessels and between test methods may have safety ramifications to the end user of the data. The large variation present in the repeatability and reproducibility of the LOC means that the current common practice of using a 2% safety margin for particle inerting (the least stringent of the inerting methods) may be insufficient to ensure dust cloud explosion mitigation. It is possible that additional study and improved laboratory proficiency as the test standard matures will bring down these repeatability and reproducibility errors. Additionally, if LOCs are reported in Safety Data Sheets without accompanying information regarding the test method or test vessel size used, the mitigation strategy may not provide adequate protection.