HEPA Filters - hdbk301094

DOE-HDBK-3010-94

5.0 Surface Contamination; Summary

5.4

HEPA FILTERS

5.4.1

Thermal Stress

HEPA filters, both unused and removed from service due to high differential pressures (clogged), were

tested using solid particles at a range of temperatures less than required for failure. The efficiencies of

the filters prior to testing for 1.8 .m particles ranged from 99.97% to 99.9999989%. Two high flow

(2000 cfm) and one 1000 cfm HEPA filters with glass fiber media and various sealant and gasket

materials were tested. No releases were found at temperatures below 150oC (175oC for one of the high

flow filters). For the 1000 cfm type filter, the release rates for temperatures from 175oC and 190oC

started at 1E-6/min and reduced to 5E-8/min within 1 hour (the lower limit of detection was 2E-8/min).

The high flow HEPAs were tested to temperatures of 200oC and 250oC with release rates starting at 2E-

4/min and 2E-5/min and reducing to 3E-7/min in 30 min and 2E-8/min in 60 min. The decay in release

was exponential during the initial 30-minutes approaching the 60-min rate asymptotically. There was no

release of contamination from a oven-fired, mineral sealant, high flow type filter at temperatures up to

350oC and the release in other types of HEPA filters is associated with the emission of smoke (binder,

degradation of inert dust on filter, pyrolysis of gaskets). Thus, it appears that the heat-induced release

from 1000 cfm HEPA filter prior to failure may be as high as 1E-5. It is assumed that HEPA filters

destroyed by flame intrusion or by the impact of air at a temperature sufficiently high to melt the glass

fiber are subjected to high temperature air to result in the release given above for heat-induced release.

The RF is assumed to be 1.0 without an experimental basis. ARFs for high-flowrate HEPA filter may be

an order of magnitude higher (1E-4). On these bases, bounding ARF and RF values for the impact of

heat upon loaded HEPA filters are assessed to be 1E-4 and 1.0.

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