A History of Research and a Review of Recent Developments

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