Explosive Stresses: Shock, Blast, and Venting

DOE-HDBK-3010-94

5.0 Surface Contamination; HEPA Filters

5.4.2

E xp losive S tresses: S h ock , B last, an d V en tin g

5.4.2.1

S h ock E ffects

Very limited experimental data have been reported on the release of collected contamination

as a result of the failure of glass fiber media HEPA filters from a dynamic pressure pulse.

Gregory et al. (February 1983) reported the release of 0.341, 1E-6 and 2E-6 of the collected

solid particles for high-flow HEPA filter during explosive transient. The large release from

the first filter was attributed to a medium that was slightly creased prior to the test and

appears to be an artifact of the test equipment. All the filters appeared to have vented by

blowout of the filter media at selected locations along the rear folds of the pleated filter mat.

The areas for the other two filters vented were very small. The total collection area of a

HEPA filter is approximately 1.8 X 105 cm2. If all the collected contaminant in the area

affected by the blowout is approximately 0.1 cm2 (a slit 1 cm long X 0.1 cm wide) and the

contaminant collection efficiency in these area is the same for the rest of the filter, the ARF

would be ~ 5E-7. Dislodging all the contaminant is difficult since much of it penetrates

into the medium. Furthermore, the affected area would appear to be the depth of medium

exposed by the rupture of the glass fibers. The test results appear to be consistent with this

type of phenomenon. Thus, it would be anticipated that the amount of the deposited material

subjected to the mechanical stress of the filter rupture is a minute fraction of the nearly

200 ft2 filter mat. Only during the initial stages of use would a large fraction of deposited

material be located in the rear fold. Thus, if the high value is discounted, ARF and RF value

of 2E-6 and 1.0 bound the data.

5.4.2.2

B last E ffects

Gregory et al. (October 1983) also performed tests on from standard (1000 cfm) glass fiber

media HEPA filters. The break pressure from static pressure loading for standard HEPA

filters ranged from 9.1 to 20.0 kPa with a mean value of 16.3 kPa. High flowrate HEPA

filter demonstrated lower structural capacity with break pressures ranging from 9.0 to

15.9 kPa with a mean value of 11.0 kPa. Removal efficiency of the standard HEPA filters

for 0.46 m diameter polystyrene latex beads in tornado conditions degraded from the

99.97% for filter under normal conditions to 98.9%. The release of the approximately 1 kg

of 0.46 m diameter PSL collected for one type of standard HEPA filters was 1.46% and

0.71% with a mean value of 0.935%. Bounding ARF and RF values are assessed to be 1E-2

and 1.0.

5.4.2.3

V en tin g of P ressurized G ases T h rou gh F ilters

See subsections 5.4.2.1 and 5.4.2.2.

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