Appendix B. Operating Temperatures for HEPA Filters

DOE-STD-1066-99

Appendix B. Operating Temperatures for HEPA Filters

To be listed by Underwriters Laboratories under UL-586 as a High Efficiency Particulate Air Filter Unit,

HEPA filters are required to: (1) withstand 750 oF (402 oC) air for 5 minutes at rated airflow capacity

and have greater than 97% DOP efficiency, and (2) withstand a spot-flame test in which a Bunsen

burner flame is placed on the filter core with no after burning when the flame is removed.

However, it can be noted that there is a rapid decrease in the tensile strength of the filter media at

about 450 oF (234 oC), and when temperatures get above 800 oF (430 oC) the fibers in the filters begin

to break and curl up leaving pinholes in the filter media. Extended exposure to temperatures above

800 oF (430 oC) will cause destruction of the case in wood-cased filters and warping of the case in

steel-cased filters, resulting in bypassing of unfiltered air.

Although HEPA filters can withstand 750 oF (402 oC) temperature for a very limited time duration, they

should not be subjected to indefinite exposure temperatures higher than 275 oF (136 oC). Longer filter

life and more reliable service as well as an operational safety factor can be obtained when normal

operating temperatures are below 200 oF (94 oC) and high temperature extremes are avoided.

Continuous operation of HEPA filters at higher temperatures is limited primarily by the filter sealant,

used to seal the filter core into the filter case. At higher temperatures, the sealants lose their strength,

causing filter failure. For example, standard urethane seals are suitable for service at 250 oF (122 oC),

while some silicone seals can withstand 500 oF (262 oC).

Since different sealants are available and different filter manufacturer's rate their filters for different

temperatures, the best practice is for ventilation system designers and operators to determine the

manufacturers limiting continuous service temperature if continuous operation at high temperatures

are necessary.

B-1