This piece of pipe is supposed to be dry unless used by the ire brigade. So if left without full drainage after use, a small amount of water will be trapped and eventually get frozen. That may clog the connections for future use (in case the next time happens under cold weather).
The picture shows LPCB approved breeching inlet (Fire department connection). I have not found the similar arrangement in UL listed fire department connection.
It is depended on the fire brigade and their equipment they use.
A side note, if this equipment is used as dry outlet for roof supply (not on street level for supply), it may also be to allow release of trapped air while the pumper below has connected.
And if the check valve leaks the water can drain from the FDC via the automatic ball drip. Big deal in cold climates. Also if the caps on the FDC are tight and the check valve leaks the length of pipe past the check valve will be pressurized. The firefighter maybe injured by the cap when loosing it or taking it off.
From the Automatic Sprinkler System Handbook 2013 Ed.
8.17.2.6* Drainage. The piping between the check valve and the outside hose coupling shall be equipped with an approved automatic drip in areas subject to freezing.
Comment Section on the above.
In the event that the check valve in the Siamese connection leaks, the purpose of the automatic drip is to drain this water to a safe location and to maintain the piping between the check valve and the hose couplings free of water. Without the automatic drip, any collected water could freeze and prevent the fire department from pumping into the system under fire conditions. This automatic drip also facilitates any maintenance of the fire department connection piping, because this portion of the pipe is already free of water. Exhibit 8.62 shows an automatic drain valve used on the fire department connections. The drain should be located at the lowest point of the fire department connection piping to allow complete drainage.
Interesting code reference from LCREP since NFPA states an "approved AUTOMATIC drip in areas subject to freezing." Seems you could only use that get-up in non-freezing areas. In freezing areas automatic is req'd, which would mean a ball drip which is all we specify anyways.
