For which type of gas mains does FDNY have no authority to shut down?

The correct answer is main valves because FDNY does not have jurisdiction over the operation of these specific valves. Main valves are typically controlled by the gas utility company and fall under their operational authority. When issues arise with gas mains or leaks, FDNY can respond and manage safety protocols, but any action involving the main valves themselves, including shutting them down, requires the involvement of the utility company that owns and operates that infrastructure.

In contrast, high pressure and medium pressure mains are within the scope of FDNY's emergency response. Although FDNY may not normally shut down these mains, they have procedures in place to work with utility companies to manage emergencies related to these types of gas lines. Curb valves, while also belonging to the utility, tend to be more accessible for fire department operations during emergencies; thus, FDNY does have procedures for engaging with them directly under certain circumstances.