Page 750 - Dust Explosions in the Process Industries

Appendix 703

to 50%, typically 25-30%, than those generated by the same dusts in larger vessels, such
as the 1 m3 standard IS0 (1985) vessel and the 20 liter Siwek sphere. It does not seem
advisable to indicate any general relationship between P,,, from the early USBM tests
and more recent data from larger vessels.

A.2.7
AXIMUM RATE OF PRESSURE RISE

These data were determined in the same Hartmann bomb experiment as the maximum
explosion pressures. However, there seems to be some justification for indicating the fol-
lowing tentative correlation between (dPldt),,, in the closed Hartmann bomb and the Ks,
from the 1 m3 standard IS0 (1985) method (see Table A.4).

Table A.4 Examples of correlation of rates of pressure rise

Note: For quite coarse powders (nonhomogeneousdust concentration distribution in Hartmann bomb) and for
very fine, cohesive powders (poor dust dispersion in Hartmann bomb), this correlation can be substantially in
error.

A.2.8
AXIMUM PERMISSIBLE O2CONCENTRATION FOR INERTING

USBM used two methods, an open glass tube with electric spark ignition and the Godbert-
Greenwald furnace at 850°C. As would be expected, the latter method gave consides-
ably lower limiting O2concentrations for inerting than the former.
Generally, the values of Table A.2 fall somewhere between the two USBM values for
similar dusts. The arithmetic mean of the two USBM values then might be compatible
with the data in Table A.2.

ASTM. (1988) “Standard Test Method for Pressure and Rate of Pressure Rise for Combustible Dusts.’’
ASTM E 1226-88. ASTMAnnual Handbook 14.02.West Conshohocken, PA: ASTM, pp. 688-698.
Berthoid, W. (1987) Bestimmung dev Mindestziindenevgie von Staub/Luft-Gemischen. Vortschritt-
berichte Series 3, no. 134, VDI. Dusseldorf VDI-Verlag.
BHA. (1987) Bvena- und Explosioizs-Kenngrossen von Staiiben. Berufsgenossenschaftliches Institut fur
Arbeitssicherheit. Bergbau-Versuchsstrecke. Institut fur Explosionsschutz und Sprengtechnik.
Bielefeld: Erich Schmidt Verlag GmbH & Co.
Dorsett, H. G., M. Jacobson, J. Nagy, et al. (1960) “Laboratory Equipment and Test Procedures for
Evaluating Explosibility of Dusts.” Report Inv. 5624. Washington, DC: US. Bureau of Mines.