What must be inspected when turning gas on in a new piping system?

When turning gas on in a new piping system, it is crucial to inspect open fittings and closed valves. This inspection ensures that there are no leaks and that all connections are secure. Open fittings must be checked to ensure they are properly capped or connected to prevent gas from escaping. Similarly, checking closed valves is vital to confirm that they are indeed closed before any gas pressure is applied to the system, safeguarding against potential leaks or other hazards.

Additionally, while examining external surroundings and measuring devices is important in a broader sense, they do not specifically address the immediate concerns of securing the integrity of the gas piping system during startup. The focus on open fittings and closed valves directly relates to the safe management and handling of pressurized gas, which is why this choice stands out as the correct approach when preparing to turn on gas in a new piping setup.