Maxitol regulators only need to be vented,
unless, the regulator is mounted horizontal and upright (with the adjustment stem straight up) and a vent limiter placed on the relief valve port. The vent limiter looks like a brass hex cap over the outlet side of the regulator. Unless these provisions are addressed, the regulator must be vented to the outside of the house. All of the maxitrol regulators I install have a vent limiter installed from the factory.
A copper vent line should be protected just like any other gas line. The only difference is it will not have constant pressure running through it. The regulator will vent only if there is a diaphragm rupture or the regulator is over-pressurized.
A maxitrol regulator
will not protect the appliances installed, it's only purpose is to bring the gas pressure to a working level. Each appliance will have it's our regulating devise to protect it whether its a regulator on a cooking range or a gas control valve on a furnace.
You may or may not hear a venting regulator. If the sound is audible, you will hear a faint hissing. On the bright side, you should certainly smell the gas.
More information can be obtained about the Maxitrol regulators on the Maxitrol website:
http://www.2psi.com/2psihome.html