Number of Valves. A hot water heating boiler shall have at least one safety relief valve which is: Officially rated; and Set to relieve at or below the maximum allowable working pressure of the boiler. A hot water supply boiler shall have at least one safety relief valve which is: Officially rated; Automatically reseating; and Set to relieve at or below the maximum allowable working pressure of the boiler. A safety relief valve with an officially rated capacity shall have pop action when tested by steam. When more than one safety relief valve is used on a hot water heating or hot water supply boiler, each additional valve shall be: Officially rated; and Set at a maximum of: 6 PSI above the maximum allowable working pressure of the boiler, for a boiler having a maximum allowable working pressure of 60 PSI or less, or 10 percent above the maximum allowable working pressure, for a boiler having a maximum allowable working pressure exceeding 60 PSI. A safety relief valve shall be: Spring loaded; and Arranged so that it cannot be reset at a pressure higher than the maximum permitted by this regulation. A material that can fail because of deterioration or vulcanization when subject to saturated steam temperature corresponding to capacity test pressure may not be used for any part. Size. Except as otherwise provided by this regulation, the standard pipe size of a safety relief valve may not be: Smaller than 3/4 inch; and Larger than 4-1/2 inches. A boiler having a heat input of 15,000 BTU per hour or less may have a rated safety relief valve of 1/2 inch standard pipe size. An inlet opening shall have an inside diameter approximately equal to, or greater than, the seat diameter. The minimum opening through any part of a valve shall be at least 1/2 inch in diameter or the equivalent area. Subject to the requirements of §I of this regulation, the minimum steam relief capacity of a pressure relief device on a boiler, in pounds per hour, shall be the greater of the capacity determined: By dividing by 1,000 the maximum BTU output at the boiler nozzle, obtained by firing any fuel for which the unit is installed; or In accordance with Table 09.12.01.11G. When operating conditions change or additional boiler heating surface is installed: Valve capacity shall be increased, if necessary, to: Meet the new conditions, and Comply with this regulation; and If there is no intervening valve, any additional valves required because of changed conditions may be installed on the outlet piping. The safety relief valve capacity for a boiler shall be sufficient to ensure that, with fuel burning equipment operated at maximum capacity, pressure cannot exceed: 6 PSI above the maximum allowable working pressure of the boiler, for a boiler having a maximum allowable working pressure of 60 PSI or less; and 10 percent above the maximum allowable working pressure, for a boiler having a maximum allowable working pressure greater than 60 PSI. If there is any doubt as to the capacity of a safety relief valve, an accumulation test shall be conducted in accordance with the ASME Code, Section VI, Recommended Rules for the Care and Operation of Heating Boilers. A valve of any type may not be placed: Between a safety relief valve and a boiler; or On a discharge pipe between a safety relief valve and the atmosphere. Discharge Pipe. A discharge pipe shall be: At least full-size; and Fitted with an open drain to prevent water from lodging in the upper part of a safety relief valve or in the discharge pipe. If a safety relief valve discharge pipe has an elbow, the: Elbow shall be located near the safety relief valve outlet; or Discharge pipe shall be securely anchored and supported. Safety relief valve discharges shall be located or piped so as not to endanger workers.