What must main shutoff valves be marked with for identification purposes?

Main shutoff valves must be marked with a metal tag or a permanent means to ensure that they can be easily and reliably identified. This requirement is crucial for safety and operational efficiency. In emergency situations or during maintenance, it is essential for trained personnel to quickly locate and operate the shutoff valves without confusion. Metal tags or permanent markings are more durable and resistant to environmental factors compared to paper labels or stickers, which may fade, wear off, or become damaged over time. Proper identification contributes significantly to safe gas handling and emergency response, making it a critical aspect of LP gas systems.