Which type of valves are prohibited from being located between a pressure relief device and the container unless a listed PRV manifold is used?

The correct choice pertains to the regulations surrounding safety measures related to propane gas systems. In propane installations, it is critical to ensure that pressure relief devices function without any obstruction that could impede their operation. The prohibition on placing shutoff valves between a pressure relief device and the container is based on safety considerations.

If a shutoff valve is located in this position, it could be inadvertently closed, preventing the pressure relief device from venting excess pressure. This could lead to hazardous conditions, including potential overpressure scenarios that can cause tanks to rupture or explode.

On the other hand, when a listed Pressure Relief Valve (PRV) manifold is utilized, it is designed to ensure that safety mechanisms are in place while still allowing necessary manual control. This makes systems safe and compliant with regulations, ensuring pressure relief devices remain effective in the event of increased pressure.

Understanding the critical role of these safety devices in propane systems emphasizes the importance of not allowing any potentially obstructive valves in key areas, thus securing both equipment integrity and user safety.