Venting of Pressurized Powder

DOE-HDBK-3010-94

4.0 Solids; Powders

and components. Shock and blast waves and associated TNT equivalents were estimated for

1.8 and 4 meter diameter flammable gas clouds. The point of detonation was assumed to be

0.75 m from the front of the glovebox.

The modelling indicated that even relatively weak shielding such as the lexan windows or

gloves of the glovebox provided significant shielding from shock waves. This was due to the

speed of the shock wave (total glovebox envelopment in 2.5 milliseconds), which would

almost completely pass over the structure and initiate reflection waves in the time it took for

shielding material to fail: "the shock wave moving inside the glovebox is approximately

spherical in shape and much weaker than the outside shock." Peak overpressures in the

glovebox ranged from ~ 8 to 28 psig at the glovebox floor and from ~ 5 to 15 psig at

0.3 m above the glovebox floor. As would be expected, the higher pressures were on the

side of the glovebox facing the explosion.

The peak velocity and density of the shock and blast wave moving across the bottom of the

glovebox were 300 m/sec and 0.004 g/cm3 respectively. Kinetic energy density was

computed from these values. Halverson and Mishima (1986) had developed an empirical

equation for wt% of powder airborne as a function of energy density. In this calculation,

powder mass was minimized (~ 30 g) to maximize energy absorbed per gram. The fraction

of material driven airborne was estimated to be 5E-3. The main uncertainty associated with

this calculation is the unaccounted potential for localized, high energy density regions that

would be expected in a non-uniform distribution. To attempt to determine the relative

severity of conditions inside the glovebox, massless tracer particles were inserted into the

model to follow flow with no drag. Particle motion indicated an absence of strong shear

forces or turning forces that might enhance breakup. Most particle movement was uniformly

to the rear of the glovebox.

The explosion study is considered to support the basic interpretation of phenomena in studies

by Mishima and Schwendiman. Based on those studies, values for ARF and RF of 5E-3 and

0.3 appear to be conservative for the suspension of a powder from a smooth, unyielding

surface from the pressure impulse generated (i.e., gas flow parallel to surface) by an

explosion. The release phenomena is considered to cover powders shielded from the direct

impact of the blast as well. Examples of such situations include powder buried under debris,

in a can/container that is uncapped by the blast, or in a glovebox with blast external to the

glovebox.

4.4.2.3

Venting of Pressurized Powder

For the entrainment due to the rapid burning of a limited volume of combustible mixture

(equal to an unconfined vapor explosion - cloud volume, <0.25 volume of container) over

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