According to NFPA 54, what must be clearly marked and posted regarding emergency shutoff valves?

The correct answer focuses on the necessity of marking and posting the location and identification of emergency shutoff valves. This requirement is critical for safety measures in natural gas and propane systems. Proper identification of emergency shutoff valves ensures that personnel can quickly and effectively respond to an emergency situation. Clear markings help facilitate immediate access to the valves, allowing for a swift shutdown of the gas supply when required, potentially preventing accidents or damage.

This aspect of NFPA 54 emphasizes the importance of preparedness and safety protocols in gas installation and maintenance. By having this information readily available and visible, it enhances the overall safety of the facility and provides essential guidance during emergencies, thereby protecting both property and individuals.