Which valve should be closed first in the priority order of gas valve closure?

In the context of gas emergencies, the priority order for closing valves is based on the need to quickly and effectively stop the flow of gas to prevent further hazards. The appliance valve should be closed first because it is located at the specific appliance where a leak or emergency is occurring, allowing for immediate isolation of the gas source from the affected area. This action mitigates the risk of fire or explosion associated with gas leaks.

Closing the appliance valve effectively limits the issue to that specific appliance, making it easier to manage the situation on-site and preventing the spread of gas to other parts of the system. After the appliance valve has been addressed, other valves such as the individual meter valve, master meter valve, or curb/service valve can be closed in a sequence based on the severity of the situation and the need for further isolation from the gas supply.

By prioritizing the closure of the appliance valve, responders can ensure a more controlled response to the emergency, minimizing the potential risks associated with gas leakage.