Emergency shutoff valves shall have _________ means of closing.

The requirement for emergency shutoff valves to have three means of closing stems from the critical safety measures necessary in handling propane and similar gases. Having multiple methods to close off the valve ensures that, in the event of an emergency, operators can quickly and effectively stop the flow of gas. This redundancy is crucial in situations where immediate action is required to prevent accidents, such as leaks or potential explosions.

The three means may include a manual shutoff, an automatic shutoff, and an emergency remote shutoff. Each of these methods offers a different approach to controlling the gas flow and can be utilized in various scenarios depending on the circumstances at hand. This layered safety protocol is essential in minimizing risks associated with propane usage, thereby enhancing overall safety in both residential and commercial contexts.

The other choices suggest a lesser number of closure methods, which would not meet the safety standards mandated for handling pressurized gases. These standards are designed to ensure that there are always reliable options available to address any potential hazards effectively.