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. Is the Healy CAS Air Breather Assembly considered an underground tank vent In the context of NEC Article 594, Group D, Division9 and 2 Hazardous Locations? As described in the above, the UST is "vented" to the bladder contained within the CAS and by design, no vapors are emitted to atmosphere. (See footnote below) Foot note:The Intent of this footnote is for reference only and to provide clarification. It Is not the Intent of the State Fire Marshal to endorse any one specific product,device or methodology. Description of Operation of the Mealy Clean Air SeparatorTM: The Healy Systems, Inc., Model 9961 Healy Clean Air SeparatorTm is astand-alone, completely mechanical de that assists in controlling the gasoline vapor emissions from a gasoline dispensing facility. it consists of a 400-gallon storage vessel with integral bladder and associated valving. It Is connected to the ullage space of the GDF storage tanks via the venting system of the under ground storage tanks. During normal operation of the GDF,with today's concentration of ®RVR vehicles approximating 20%,the storage tank ullage space will usually operate in the"0" to negative(up to 6"WC P/V cracking pressure)pressure range. During"closed"periods of the GDF,the ullage pressure will usually begin to increase due to vapor growth inherent in the process of introducing air into the UST's. If the pressure goes slightly above atmospheric the vapor from the UST's will flow into the internal bladder. Conversely, when 4 VR refueling begins and the UST pressure fails below atmospheric,the vapor internal to the bladder will be drawn back into the UST until the bladder is fully collapsed waiting for the next cycle. The Clean Air SeparatorTm in over two and one half years(installed late September of 2002)of being in operation at our C.A. .B.test site in Sacramento has been evaluated repeatedly to see if there is any liquid condensation in either the bladder or the space between the inner wall of the vessel and outer wall of the bladder. To date there has been no liquid found in either area.