For gas systems serving multiple users, on which side should the gas piping systems remain separate?

For gas systems serving multiple users, the correct demarcation for maintaining separate gas piping systems is on the outlet side of meters. This separation is essential to ensure that each user has their own individually metered supply of gas. By keeping the piping systems separate after the meters, it allows for accurate measurement of gas usage for each user without interference or backflow from other users' systems.

Having separate systems at this juncture allows for the responsibility of gas usage to be assigned effectively to each user, promoting accountability and ease of billing. Moreover, this arrangement enhances safety; any issues with gas systems can be addressed without affecting the supply to other users, thereby ensuring system integrity and compliance with safety standards.

The other possible locations mentioned in the question do not serve the same purpose for separation. For example, separating before the main supply would mix various user needs before they can be individually accounted for. Similarly, issues related to building access points pertain more to service access rather than ownership and usage accountability after the gas reaches individual users.