Page 187 - Dust Explosions in the Process Industries

760 Dust Explosions in the Process Industries

the hair, and the skin, of the boy who was in the warehouse, the cause of it must be attributed to the
fire of the fine particles of the flour, which, floating in the atmosphere, were kindled by the inflam-
mable air, in the same manner as the powder from the stamina of certain vegetables, (particularly of
the pine, and of some mosses,) when thrown in the air, takes fire if any light is applied to it.
But it may be objected, that as the flour was not at all damp, and had not any sensible degree of
heat, there should not be any fermentation in it, and consequently no inflammable air should be pro-
duced: to this I answer,
First. That flour is never entirely free from humidity, as is evidently shewn by distillation.
Secondly. That although the degree of heat was not so great as to set free inflammable air by fer-
mentation, a sufficient quantity was set free, by what may be called a mechanical mean, to inflame
upon the contact of light; and to disengage, at the same time, all that which communicated with the
atmospheric air.
Thirdly. We must recollect that flour also furnishes alkaline inflammable air, which is produced
from the glutinous vegeto-animal part of the corn; and we know that this kind of inflammable air is
of a very active nature.
After having described this singular event, I shall beg leave to collect together, in this place, all
the known facts respecting spontaneous inflammations produced by different substances. A circum-
stantial account of these phaenomena cannot but be very interesting to those concerned in govern-
ment; not only as it may tend to prevent the unhappy accidents which result from them, but also as
it may sometimes hinder the suspicion and persecution of innocent persons, on account of events which
are produced merely by natural causes.

2.3
GRAIN DUST EXPLOSIONS IN NORWAY

2.3.1
WHEAT GRAIN DUST, STAVANGER PORT SILO, JUNE 1970

The explosion, which was discussed by Astad and Mo (personal communicationsfrom
A. Astad, director, Stavanger Port Silo, and A. Mo, Norwegian Grain Corporation, 1970),
occurred in Norway’s largest and newly built import grain silo in Stavanger on a hot,
dry summer day. Fortunately, no persons were killed, but some workers suffered first-
degree burns. Although the extent of flame propagation was considerable, the material
damage was moderate, due to the comparatively strong reinforced concrete structure of
the buildings and the venting through existing openings.
The entire event lasted for a period of about 25-30 seconds, during which a sequence
of six or seven distinct, major explosions were heard. In the middle of this sequence was
an interval of 10-12 seconds.The flame propagated a total distance of about 1500meters,
through a number of bucket elevators, horizontal conveyors, ducting, filters, and rooms in
the building. Dust explosions occurred in six of the large, cylindrical storage silos of total
volume 2000 m3 each, in one large, slightly smaller silo, in seven of the slimmer, inter-
mediate silos of capacities400 or 1000m3,in one 150m3silo, and in seven loading-out silos
with capacities of 50 m3each. The six largest silos had no venting, whereas the explosions
in the large silo of slightly smaller volume and in all the intermediate and loading-out silos
were vented through 0.4 m2manholes, which had their covers flung open.
It is of interest to note that only one silo was damaged in the incident, namely, one of
the six unvented,large storagesilos, which had its roof blown up, as shown in Figure 2.2.
It is thereforeclear that the maximum explosion pressures in all the other 21 silos, vented
and unvented, were lower than about 0.2 bar(g), which would be required to blow up
the actual type of silo roof.