For years now, many of us have been wary of UV exhaust hoods. Unsure how well they would work if specified in a project and unsure if they would be the correct choice. Some have been swayed because there is a maintenance cost involved. Yet we know duct cleaning does not come cheap, but that is another story.

Another question involved the type of cooking that would be exhausted by the UV hood? And what was all this talk about no grease, only a fine gray powder? How can that be a fact? We all know, grease is thick and gooey. Should we believe the marketing hype that it magically changes to powder via the UVC process?

A task group within NFPA 96 was asked last year to prepare a preliminary report addressing how ultra violet lamp technology works in commercial kitchen exhaust hoods. The preliminary findings were submitted late last year to the full NFPA 96 Committee as Version 1.1, dated October 25, 2006. UP YOUR STACK will provide you with the highlights of these preliminary findings.

• UV exhaust systems use a C lamp (UVC) to remove grease. The wavelength of the lamp operates at 180-280 nanometers. The high energy light along with the ozone that is created, breakdown both grease particles and grease vapors into apparently benign end products.
• Grease ducts beyond the UVC system appear to be further cleansed as a result of continued system operation during non-cooking periods.
• UVC appears to work best on vapors and particles less than <5.0 microns.
• Many systems include high efficiency mechanical filters beyond the UVC system to remove micron particles greater than >5 microns.
• The type of cooking will affect the performance of a UVC system.
• Cooking temperatures, water content, type of fryer oil and age of the oil will affect the ability of the UVC system to remove grease from the exhaust air stream.
• Using empirical measurements, UVC apparently reduces odors in the cooking effluent. Due to a lack of test method, this claim is not quantified.
• Longer duct systems provide more reaction time for the ozone to work effectively.
• Maintenance is required to manually clean the bulbs and keep them free of residue.

We have limited the suggested draft report findings to items of general interest.

Definitions: Webster defines nanometer as a unit of measure equal to one billionth of a meter. Meter is defined as the distance light travels in a vacuum in one second. That number is 1/299,792,458 and of course one meter is 39.37 inches. Finally, a micron is defined as the millionth part of a meter.

We can add some further items of interest not covered in the report. Ultra violet bulbs come in three types. UVA and UVB versions produce wavelengths unsuitable for the grease removal process. UVC bulbs are defined as short wave bulbs with some models capable of producing ozone.

Referring to the maintenance factor, bulbs which can vary from four to eight in quantity by various manufacturers must be accessed and wiped as often as necessary. Usually the manufacturer provides a hinged panel that makes access easy from a stool or short ladder.

In test stores, one chain requires their employees to wipe them daily. Other companies clean them less often depending on the amount of grease attaching itself to the outer plastic safety shell surrounding the bulbs. Cleaning one system or section within a system should usually take only a few minutes each. Interlocks turn off the light during cleaning to protect one’s eyes.

With current life expectancy of UVC bulbs, replacement bulbs are recommended every six months by manufacturers. These have been rated at 8,000 hours, but we were recently told that new longer life bulbs may be making their way into the market place. Bulbs do lose their effectiveness while still appearing to work as they age.

We are aware that at least one manufacturer has been working to establish scientifically why and how ultra violet works in CKV hoods. This data is currently lacking. We will be following these developments and hope to have some definitive information available during 2007.

UP YOUR STACK hopes that this information takes some of the mystery out of UVC systems. Be on the lookout for more articles as we learn more from NFPA 96 and others. Please note that the NFPA 96 White Paper was presented as a draft and is not to be considered as the final word.