(54cb) Quantitative Evaluation of "Unconfined" Dust-Cloud Explosion Hazards

QUANTITATIVE EVALUATION

OF “UNCONFINED” DUST-CLOUD
EXPLOSION HAZARDS

A presentation to the 14^th
Global Congress on Process Safety

April 22 to 26, 2018

at the Orlando World Center Marriott

Abstract

When performing
an Occupied Building Risk Assessment, it may be necessary to determine the
blast pressure and blast impulse resulting from explosion of a mixture of
combustible dust and air in a nearby building or – possibly – outside a
building.  These scenarios would be similar to a confined explosion of a mixture
of air and a flammable vapor [or gas] in a building or an unconfined vapor
cloud explosion.

Ignition of
dense clouds of combustible dusts with low values of Deflagration Index [Kst]
are unlikely to yield significant blast pressures.  However, tests involving
ignition of dusts with values of Kst above 300 bar-meters per second show that
blast effects could be hazardous.

Although
more-sophisticated methods for evaluating explosion hazards are available, the
“TNT-Equivalence” method – with a “virtual distance” to a TNT source – is simple
and provides a good measure of blast hazards.  The heat of combustion of the
dust would be required, together with a value for the Deflagration Index. 
Also, if the dust explosion is partially confined within a building or other
structure, the pressure at which the structure would “burst” would be needed. 

This
presentation provides a calculation method for estimating blast pressure and
blast impulse, as based on the TNT equivalence of the combustible-dust
explosion.