American Society of Engineers

Standard No. 1013

B.1.2 It is required that a backflow preventor assembly not be installed in an underground vault or pit if the unit vents to atmosphere like an ASSE standard 1013 assembly.

B.1.5 The backflow prevention assembly should be installed in an accessible location with sufficient clearance to permit periodic testing and maintenance.

B.1.8 The relief valve of the reduced pressure assembly may discharge large quantities of water/liquid. Special considerations must be given to the location of the assembly installation to ensure that adequate drainage is provided, as any discharge will damage the surrounding.

B.2.2 ...Generally, the installation should be made so that no part of the unit should be submerged...

Mueller - ...The installation should be made so that no part of the unit can be submerged. Units may be installed outdoors only if the device is protected from freeze.

National Fire Protection Association

3-51.2 When water filled supply pipes, risers, system risers, or feed mains pass through open areas, cold rooms, passageways, or other areas exposed to freezing, the pipes shall be protected against freeze by insulating covering, frost-proof casings, or other reliable means capable of maintaining a minimum temperature of 40° F.