Which backflow protection method cannot be used in a high hazard scenario?

In a high hazard scenario, dual check backflow preventers are not sufficient due to their design and the level of protection they provide. A dual check device consists of two check valves in series, which offers some level of protection against backflow. However, it is not designed to handle situations where there is a significant risk of contamination or where the hazards involved are severe. This includes scenarios with toxic substances or potential pollutants that could severely impact public health or safety if backflow were to occur.

On the other hand, an air gap creates a physical separation between the water supply and any potential contamination source, making it highly effective in the most hazardous situations. The reduced pressure zone (RPZ) assembly is also specifically engineered to prevent backflow in high hazard applications, providing a robust defense against backpressure and backsiphonage. Thus, while dual check devices may be suitable for lower hazard situations, they are not adequate for high hazard risks, emphasizing why they cannot be utilized in such conditions.