A History of Research and a Review of Recent Developments
A History of Research and a Review of Recent Developments
A History of Research and a Review of Recent Developments
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Gas explosions 63<br />
reported by Palmer [3.11] in a book on dust explosions <strong>and</strong> fires. The sugars<br />
were dextrose, sucrose <strong>and</strong> raffinose, <strong>and</strong> the rates <strong>of</strong> pressure rise (dp/dt) for<br />
any given pressure were found to be given by an equation <strong>of</strong> the form<br />
(dp/dt)=Ap–Bp 2 .<br />
(3.5)<br />
Experiments on peat dust explosions (peat can be thought <strong>of</strong> as geologically<br />
young coal) have been carried out in Finl<strong>and</strong>, with varying particle size<br />
distributions <strong>and</strong> moisture content. At zero moisture content average particle<br />
diameters <strong>of</strong> 54, 96 <strong>and</strong> 165 microns gave rise to values <strong>of</strong> p m <strong>of</strong> 8.4, 7.8 <strong>and</strong> 7.7<br />
bar respectively, <strong>and</strong> values <strong>of</strong> (dp/dt) m <strong>of</strong> 610, 413 <strong>and</strong> 395 bar/sec. The times<br />
from ignition to peak pressure were 35, 47 <strong>and</strong> 45 msec. A moisture content <strong>of</strong><br />
14.1% by weight with an average particle diameter <strong>of</strong> 38 micron gave p m= 8.4<br />
bar, (dp/dt) m=513 bar/sec. A moisture content <strong>of</strong> 33.6% by weight with a particle<br />
diameter <strong>of</strong> 72 micron gave values <strong>of</strong> 7.2 <strong>and</strong> 248 respectively. In reporting the<br />
Finnish experiments Kjäldman [3.12] also reported analytical work to model<br />
the explosive process. Essenhigh [3.13], however, has made the point that there<br />
has not been a great advancement in theoretical methods in recent times, <strong>and</strong><br />
that most research since the late eighteenth century has been experimental. The<br />
main safety measure against dust explosions is the efficient venting <strong>of</strong> bins <strong>and</strong><br />
containers, <strong>and</strong> this is dealt with in detail in reference [3.11] <strong>and</strong> in an industrial<br />
fellowship report issued by the Institution <strong>of</strong> Chemical Engineers [3.14].<br />
In an appendix to his book, Palmer gives the explosion properties <strong>of</strong> a<br />
comprehensive selection <strong>of</strong> dusts, powders <strong>and</strong> particles, ranging from tea,<br />
tobacco, soap <strong>and</strong> rice to chemically complex cellulose, polyethylene <strong>and</strong> sodium<br />
powders. A selection <strong>of</strong> maximum explosion pressures in lb/in 2 <strong>and</strong> rates <strong>of</strong><br />
pressure rise in lb/in 2 /sec has been made by the author using Palmer’s figures,<br />
<strong>and</strong> is given in Table 3.1.<br />
Further information on pressures <strong>and</strong> pressure rise rates in relation to dust<br />
concentration has been summarized in ref. [2.38], using the earlier publication<br />
by Bartknecht [3.15].<br />
3.3 GAS EXPLOSIONS<br />
The best-known examples <strong>of</strong> gas explosions are associated with coal mining<br />
<strong>and</strong> the use <strong>of</strong> gas for domestic heating <strong>and</strong> lighting purposes. A major hazard<br />
in mining operations has always been the explosion <strong>of</strong> coal dust <strong>and</strong> firedamp<br />
(methane gas). Wherever coal is found underground there is likely to be methane,<br />
a product <strong>of</strong> the ageless decomposition <strong>of</strong> organic matter in coal, which is<br />
highly inflammable <strong>and</strong> difficult to detect. We are told that the ‘working’ <strong>of</strong><br />
methane in a coal seam makes a sound like the faint humming <strong>of</strong> bees.<br />
From the earliest time miners were conscious <strong>of</strong> the danger <strong>of</strong> using naked<br />
flames for light when working underground, <strong>and</strong> problems like this led to the<br />
well-known development <strong>of</strong> the safety lamp by Sir Humphrey Davy in 1815,