Page 715 - Dust Explosions in the Process Industries

682 Dust Explosions in the Process industries

A.l .I .2
Initial State and Composition of the Cas in Which the Dust
Is Dispersed or Deposited

The data in Table A. 1 apply to
Atmospheric pressure (from -0.2 to +0.2 bar(g)).
Oxygen content of air (from 18 to 22 vol% 0,).
Normal ambient temperature (from 0 to 40°C).

In general, P,,, and under certain conditions also (dPldt),, or Kst, increase propor-
tionally with the absolute initial pressure. Increased oxygen fraction in the atmosphere
increases both the ignitability and the explosibility, whereas a lower oxygen content
than in air reduces the hazard correspondingly. Increased initial temperature increases
the ignition sensitivity (reduces MIE). Normally, data for conditions that deviate sig-
nificantly from the standard test conditions have to be determined specifically in each
case.
If the gas phase contains some combustible gas or vapor, even in concentrationscon-
siderably below the lower explosibility limit for the gas or vapor, hybrid effects can give
rise to considerableincrease of both ignition sensitivityand explosibility.In such cases,
specific tests definitely have to be conducted.

A.1.2
COMMENTS ON THE VARIOUS ITEMS IN TABLE A.l

A.1.2.1
Selection and Identification of Dusts

The original table, published in German by the BIA (1987), contains nearly 1900
dusts. Therefore, the selection of about 375 dusts in Table A. 1 constitutes about 20%
of those in the original tables. When making the selection, the samples of a given dust
material that gave the most severe test data were normally preferred. In addition,
sequences for some given dust materials showing systematic effects of, for example.
moisture content or particle size were included. Examples of this are data for peat and
aluminum.
Inthe original German table, the dusts are identifiedby a code number, which has been
omitted here. However, the sequence of the dusts in the condensed table is identical to
that in the originaltable. If required, the dusts in the condensedtable can be easily iden-
tified in the original German table by means of the particle size data and the ignitability
and explosibility data.

A.1.2.2
Particle Size Distribution

Most of the dusts were tested as received. However, in some cases, fractions passing a
63 ,um sieve were tested.