HEPA housings can undergo a decontamination process for multiple reasons. Most frequently, HEPA housings are decontaminated prior to filter changeout. They can also be decontaminated as part of a yearly routine or during construction/renovation. HEPA housings can be on the supply or exhaust side of an HVAC system for a facility. On the supply side, they are purifying the incoming air to maintain sterility for a clean facility. On the exhaust side, they are purifying the air exhausting a facility that works with biologically hazardous organisms to prevent their escape.
Formaldehyde used to be the most prevalent decontamination method used to attain a 6-log sporicidal kill. This method was effective, but the process typically took over 12 hours and held considerable safety concerns. Formaldehyde is a carcinogen known to leave residues behind. Both of these attributes are concerning, especially if a HEPA housing is on the supply side of the room.
Hydrogen peroxide vapor is another decontamination method utilized for HEPA housing decontamination. Due to adsorption issues into the HEPA filter itself, aerating HEPA housings can take considerably longer and typically lasts overnight. Adsorption into the filter material can cause uneven concentration amounts on either side of the filter too, potentially limiting the success of the decontamination.
Chlorine dioxide has become a more optimal decontamination method, especially when considering HEPA housings. Chlorine dioxide gas works faster, with overall cycle times between 1.5-3 hours. Part of this is because chlorine dioxide does not leave a residue and the aeration time is shorter. For exhaust HEPA housings, aeration is accomplished by simply turning on the exhaust blower and opening the “infeed” and “exhaust” dampers on a HEPA housing. This method aerates a HEPA housing in under a minute. For supply HEPA housings, this is accomplished by using a carbon scrubber to break down the CD gas. This method aerates a HEPA housing in under an hour.
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