Section 162.161-4 - Construction(a) Each pressure vessel must comply with 46 CFR 147.60(a) and (b) .(b) Each system must be capable of operation without an external power source.(c) Manual actuation for the system must be by mechanical or pneumatic means.(d) Automatically actuated systems must be released by pneumatic or fusible element detection systems.(e) Each system installed with the extinguishing agent cylinders stored inside a protected space of 6,000 cubic feet or less must use automatic actuation as the primary means of actuation and have a remote backup manual mechanical actuator.(f) Each container charged with nitrogen must have a pressure gauge.