507.21 Venting of Gas Appliance Pressure Regula-

tors. Venting of gas appliance pressure regulators shall comply with the following requirements: (1) Appliance pressure regulators requiring access to the

atmosphere for successful operation shall be equipped with vent piping leading outdoors or, if the regulator vent is an integral part of the appliance, into the combustion chamber adjacent to a continuous pilot, unless constructed or equipped with a vent limiting means to limit the escape of gas from the vent opening in the event of diaphragm failure. (2) Vent limiting means shall be employed on listed appli ance pressure regulators only. (3) In the case of vents leading outdoors, means shall be

employed to prevent water from entering this piping and also to prevent blockage of vents by insects and foreign matter. (4) Under no circumstances shall a regulator be vented to the

appliance flue or exhaust system. (5) In the case of vents entering the combustion chamber,

the vent shall be located so the escaping gas is readily ignited by the pilot and the heat liberated thereby does not adversely affect the normal operation of the safety shutoff system. The terminus of the vent shall be securely held in a fixed position relative to the pilot. For manufactured gas, the need for a flame arrester in the vent piping shall be determined. (6) A vent line(s) from an appliance pressure regulator and a

bleed line(s) from a diaphragm-type valve shall not be connected to a common manifold terminating in a combustion chamber. Vent lines shall not terminate in positive-pressure-type combustion chambers. [NFPA 54:9.1.19]