The installation procedure for underground piping shall protect the piping from
physical damage while being backfilled. [NFPA 99:5.1.10.11.5 .2]
If underground piping is protected by a conduit, cover, or other enclosure, the following requirements shall be met:
- Access shall be provided at the joints for visual inspection and leak testing.
- The conduit, cover, or enclosure shall be self-draining and not retain groundwater in prolonged contact with the pipe. [NFPA 99:5.1.10 .11.5.3]
Buried piping that will be subject to surface loads shall be buried at a depth that will protect the piping or its enclosure from excessive stresses. [NFPA 99:5.1.10.11.5.4]
The minimum backfilled cover above the top of the pipe or its enclosure for buried
piping outside of buildings shall be 36 inches (914 mm), except that the minimum cover shall be permitted to be reduced to 18 inches (457 mm) where there is no potential for damage from surface loads or surface conditions. [NFPA 99:5.1.10.11.5.5]
Trenches shall be excavated so that the pipe or its enclosure has firm, substantially continuous bearing on the bottom of the trench. [NFPA 99:5.1.10.11.5 .6]
Backfill shall be clean, free from material that can damage the pipe, and compacted. [NFPA 99:5.1.10.11.5.7]
A continuous tape or marker placed immediately above the pipe, or its enclosure shall clearly identify the pipeline by specific name. [NFPA 99:5.1.10.11.5.8]
A continuous warning means shall also be provided above the pipeline at approximately one-half the depth of burial. [NFPA 99:5.1.10.11.5.9]
Where underground piping is installed through a wall sleeve, the outdoor end of the sleeve shall be sealed to prevent the entrance of groundwater into the building. [NFPA 99:5.1.10.11.5.10]