Air Line Rupture cont'd

DOE-HDBK-3010-94

7.0 Application Examples; Feed Preparation Example

airflows in localized areas. The bounding ARF and RF assigned for this phenomena

are either 5E-3 and 0.4 (subsection 4.4.2.3.2) for venting of pressurized volumes at

pressures less than 0.17 MPag or 5E-3 and 0.3 (subsection 4.4.2.2.2) for accelerated

airflow parallel to the surface of powders. The higher value is arbitrarily selected,

and the maximum initial respirable source term, neglecting the resuspension

contribution of material not in proximity to the airflow, is:

5000 g * 0.4 * 5E-3 * 0.4 = 4 g

The most extreme case is if the break results in: (1) the pressurized air line pointing

directly at exposed powder no more than 20 cm from the pressurized release; (2) the

pressurized air pointed downward at the powder so that the underlying metal surface

supports maximum impact; and (3) optimal angle of impact with the powder. In such a

case, larger amounts of material are driven airborne, with the total respirable source

term being directly dependent on the nature of the powder (adhesiveness and size

distribution), characteristics of the surface, and angle and velocity of gas impacting

the powder. For all practical intents and purposes, meaningfully estimating a source

term for such a highly unlikely condition is an indeterminate problem.

All of the releases discussed above are inside the glovebox and would be precluded by

normal use of a flow-restricting orifice in the air line feeding the glovebox. Because

the basic purpose of a flow-restricting orifice is to prevent disrupting confinement

differential pressures, the application of the release data to the case of glovebox

overpressurization is briefly considered as well. If the line break is not in close

proximity to any material, the effect on the powder in the glovebox is bounded by the

aerodynamic entrainment calculation already made. Given that a significant

pressurization is not expected to last more than several seconds, the overall airborne

release from process material is, at most, in the milligram range.

The other major potential release mechanism is reverse flow through glovebox-

mounted HEPA filters. The reverse pressurizations typically experienced in a

glovebox environment are not large enough to damage filters, and the bounding value

for a high pressure pulse of gas through filters defined in this handbook is

conservative for the effect. The bounding ARF and RF assigned for this phenomena

are 2E-6 and 1.0 (subsection 5.4.2.1). If a typical dirty glovebox filter loading of

10 g is assumed, the maximum initial respirable source term is:

10 g * 1.0 * 2E-6 * 1.0 = 20 g

As is expected from historical experience, the estimated releases are not large.

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