Vannic,
Vent lines on gas regulators are to be sized in case the diaphram in the regulator breaks. You want to be able to vent what is upstream of the regulator to a safe outdoor location in case this happens. This is to protect the downstrean equipment - you should also have a high pressure gas switch downstream of the regulator and shut off valve(s).
Some regulators come with internal over pressure relief valves and some application require either an internal or external over pressure relief valve.
In your case you have small boilers - my specialty is larger industrial applications. You might have to check with your local insurance company to get specifics - Factory Mutual might be of some help.
Good Luck!