4.12.710 SAFETY RELIEF DEVICES
(1) Every container used in the storage or transporting of anhydrous ammonia shall be provided with one or more safety relief valves of the spring-loaded type. The discharge from safety relief valves shall be vented away from the container, upward and unobstructed into the atmosphere. All safety relief valve discharge openings shall have raincaps that will allow free discharge of the vapor and prevent the entrance of water. Provision shall be made for draining condensation which may accumulate. The rate of discharge shall be in accordance with Table A.
(2) Container safety relief valves shall be set to start-to-discharge in relation to the design pressure of the container as follows:
department of transportation (as required by Hazardous Materials Regulations, section 173.315 (I-3 and 3) ) .
(3) Safety relief devices shall be constructed to discharge at not less than the rates required in ARM 4.12.710(1) before the pressure is in excess of 120 percent (not including the 10% tolerance referred to in ARA 4.12.710(2) of the maximum permitted start-to-discharge pressure setting of the device.
(4) Safety relief valves shall be arranged so the possibility of tampering will be minimized. If the pressure setting adjustment is external, the relief valve adjustment shall be sealed.
(5) Shutoff valves shall not be installed between the safety relief valves and the containers, except a shutoff valve may be used where the arrangement of this valve always affords required capacity flow through the relief valves. Examples:
(a) A three-way valve installed under two safety relief valves, each of which has the required rate of discharge and is so installed as to allow either of the safety valves to be closed, but does not allow both safety valves to be closed at the same time.
(b) Two separate relief valves are installed with individual shutoff valves. In this case, the two shutoff valve stems shall be mechanically interconnected in a manner which will allow full required flow of one safety relief valve at all times.
(c) A safety relief valve manifold which allows one valve of two, three, four, or more to be closed and the remaining valve(s) will provide not less than the rate of discharge to allow the proper cubic feet per minute of air in relation to tank capacity as shown in Table A.
(6) Safety relief valves shall have direct communication with the vapor space of the container.
(7) Each safety relief valve used with systems shall be plainly and permanently marked as follows:
(a) with the letters "AA" or the symbol "NH3";
(b) the pressure in psig at which the valve is set to start-to-discharge;
(c) the rate of discharge of the valve in cubic feet per minute of the air at 60 degrees F and atmospheric pressure (14.7 psia) ;
(d) the manufacturer's name and catalog number.
(8) The flow capacity of the safety relief valve shall not be restricted by any connection to it on either the upstream or downstream side.
(9) The manufacturer or supplier of a safety relief valve manifold shall furnish complete data showing the flow rating through the combined assembly of the manifold with safety relief valves installed.
(10) A hydrostatic relief valve, venting to atmosphere at a safe location, shall be installed between each pair of shutoff valves in an ammonia line where the liquid may be trapped, except when the hose or line is protected by an internal equalizing valve with a differential pressure so designed as to not exceed 50 psig. The start-to-discharge pressure of hydrostatic relief valves shall be not less than 350 psig and not in excess of 400 psig.
(11) Discharge from safety relief devices shall not terminate within or beneath any building.