Free-Fall Spill and Impaction Stress

DOE-HDBK-3010-94

5.0 Surface Contamination; HEPA Filters

5.4.4

F ree-F all S p ill an d I mp action S tres s

Material accumulated on the filter media could be dislodged by the jarring of the media/filter

by a single severe shock (e.g., earthquake, impact of heavy object such as aircraft engines,

forklift) or by mechanical vibration. In the case of a severe shock, it is assumed that the

housing holding the filter banks would also be compromised and material made airborne both

in and out of the housing are of concern. The media is a relatively fragile material with

considerable flexibility and dislodging only the accumulated particles does not appear to be

consistent with experience. Rather, the fragmentation of the media by the vibration/shock

appears to be principal mode for particle generation as shown in Table A.55 from Arnold

(1986) where filters without accumulated Pu (although other inert, airborne materials may be

collected) release the same fraction of particles as loaded filters within each filter set.

Arnold (1986) reported on a series of studies conducted at the Rocky Flats Plant on the

particles generated by HEPA filters (large plenum sized filters, 2-ft x 2-ft x 1-ft), and filters

used to seal the exhaust outlets on gloveboxes (8-in x 8-in x 6-in and 12-in x 12-in x 6-in)

subjected to repetitive slamming on a hard, unyielding surface and mechanical crushing. In

one study, 30 plenum-sized filters, wrapped in two layers of plastic, were mechanically

crushed and approximately 0.75 lb of material in an outer box holding the filter during

transport were collected. Less than 5 wt/o of the collected material was in the size range of

<200 m (LLD, sieves used) and <0.5 wt/o was <25 m. All the filter media

disintegrated under test conditions for filter from plenum FU2B (from a recovery facility

where strong acid vapors are present in the effluents) and the particulate weight listed is that

for all the media. The Matrix Weight listed in that table for filters from other plena is the

total weight of the filters and ranges from 13,190 g to 24,380 g. On that basis, the media

represents from 5.3% to 12.2% of the total filter weight. The average weight of a plenum

sized filter in this study was given as 17.613 kg (the average weight of plenum sized filters

was 18.18 kg and 18.1 kg in other studies) and the total weight of 30 plenum sized filters

would be 528.39 kg. The total mass of particles collected, 255 g, represents 0.0483 % of

the total filter weight. If it is conservatively assumed that the total media mass is 5% of the

total filter weight, the particles collected represent 0.97% of the filter media mass and the

fraction <25 m LLD is 0.005% of the filter media mass.

Thirty plenum-sized filters were crushed in a hydraulic press and a total of 34.1 g of

particles collected. The total filter weight was 528.29 kg with a media mass of 26.42 kg

under the assumption that the media mass is 5 wt/o of the total filter mass. Thus, the

particles represent 0.13 wt/o of the total media mass. The size distribution of particles

generated was found to be 8.525% <200 m with no measurement of the 10 m fraction.

In the other portions of this study, the 10 m fraction was no greater than 10% of the

<200 m fraction and on this basis, the fraction 10 m and less would represent 0.0013

wt/o of the media mass.

Page 5-32