Dust/Vapour Explosions: Hybrid Behaviors? - Summary

Dust/Vapour Explosions: Hybrid Behaviors? – Summary

1-Sentence-Summary: Addition of flammable vapour (diisopropyl ether) to nicotinic acid increases the maximum pressure and maximum rate of pressure rise in a non-linear manner where the end result can be worse than the two fuels individually.

Authors: O. Dufaud, L. Perrin, and M. Traore

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Dust/Vapour Explosions: Hybrid Behaviors? - Summary

The authors of this paper perform experimental testing in a 20 L explosion chamber. The dust is nicotinic acid (B3 vitamin, also known as niacin) with a particle size defined by d10, d50, and d90 of 12, 26, and 104 µm, respectively. The vapour is diisopropyle ether which is relevant to the pharmaceutical industry.

The experimental tests were completed following the ISO 6184-3 standard using two pyrotechnic chemical ignitors of 5 kJ each. Summary plots of maximum pressure and maximum rate of pressure rise for the different mixtures tested are given along with analysis of the results.

Three of the main findings from this paper are:

  1. More than additive effects for maximum pressure and maximum rate of pressure rise are seen for the hybrid mixtures.
  2. Maximum pressure appears to change linearly with mixed volume fraction while rate of pressure rise increase is non-linear.
  3. Addition of either fuel below its flammability limit can increase the explosion parameter of the other fuel.

The following sections outline the main findings in more detail. The interested reader is encouraged to view the complete article at the link provided below.

Finding #1: Hybrid mixtures can have more than additive effects on explosion consequence

The authors found that there existed hybrid mixtures with larger maximum pressure and maximum rate of pressure rise than either of the fuels individually. For the fuels alone, 2.75% vol diisopropyl ether resulted in 8.8 bar gauge pressure, and 500 g/m3 niacin resulted in 8.4 bar gauge pressure. However, 9 bar gauge pressure was achieved for mixtures of 1.4% vol dissopropyl ether and 250 g/m3 niacin.

For maximum rate of pressure rise, the largest values for the fuels individually occurred for 2.75% vol diisopropyl ether (1310 bar/s), and for 750 g/m3 niacin (790 g/m3). The maximum hybrid rate of pressure rise was found to be around 1600 bar/s for approximetly 1.5% vol gas and 225 g/m3 dust.

Finding #2: Maximum rate of pressure rise may change in a non-linear manner with total fuel in the mixture

The plotted results in the paper demonstrate that the hybrid mixtures containing the maximum pressure lie on a straight line between the concentrations resulting in the maximum pressures for the two fuels individually. For example the 9 bar gauge maximum hybrid pressure lies on a straight line between 2.75% by vol diisopropyl ether and 500 g/m3 (approximately at the halfway point, 1.375% vol, 250 g/m3). Any mixtures off this straight line appear to be fuel lean or fuel rich, and result in a lower maximum pressure.

The plotted results for maximum rate of pressure rise show a non-linear trend with overall fuel mixture. The maximum hybrid value occurs at approximately one half of the gas concentration resulting in the maximum pressure, but at approximately 25% of the dust concentration. Also, the pressure rise rate falls off rapidly after this point with more dust addition. Overall, hybrid maximum rate of pressure rise is more complex than maximum pressure.

Finding #3: Addition of either fuel below its flammability limit has a large impact

The authors found that the addition of small amounts of diisopropyl ether or niacin to the other, had a large impact on the explosion consequences. For example the addition of of small amounts of diisopropyl ether (0.5% vol) to 250 g/m3 niacin caused the maximum pressure and maximum rate of pressure rise to increase from 7.3 bar gauge and 685 bar/s, to 8 bar gauge and 1100 bar/s.

My Personal Take-Aways From
“Dust/vapour explosions: Hybrid behaviors?”

This paper shows some very interesting results for hybrid mixtures. It is one of the only articles in the field to show “more than additive” effects for hybrid mixtures. This may be due to the kinetics of the on-board oxygen molecules in diisoproply ether (C6H14O) or niacin (C6NH5O2). Different flame temperatures due to the hybrid explosion may release these molecules allowing for further oxidation of the fuel. The use of strong chemical ignitors may also promote this behavior. This finding would have important implications for ignition sources in industry.

The use of contour plots in this paper make it difficult to extract exact quantitative information from the explosion results. Also, pressure-time traces such as those given in Pilao et al., 2006 and Denkevits, 2007, may make it easier to diagnose the more than additive and non-linear effects. It would also be useful to determine how these authors injected the vapour into the chamber, as this could be helpful to others in the field.

This article would be useful for anyone researching explosion of hybrid mixtures with more complex molecules than the typical hydrocarbons that have been studied previously. The data is also useful for those in the pharmaceutical industry where hybrid mixtures of this type can arise from excipient/solvent processes. These authors subsequently published explosion data for other hybrid mixtures relevant to the pharmaceutical industry (magnesium starate/ethanol and antibiotic/toluene) that would also be usefull (see Dufaud et al., 2009).

Full Citation:

  • O. Dufaud, L. Perrin, and M. TraorĂ©, “Dust/vapour explosions: Hybrid behaviours?,” Journal of loss prevention in the process industries, vol. 21, pp. 481-484, 2008.
    title={Dust/vapour explosions: {H}ybrid behaviours?},
    author={Dufaud, O. and Perrin, L. and Traor\'{e}, M.},
    journal={Journal of Loss Prevention in the Process Industries},

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