Which of the following cannot be used for backflow protection in a high hazard?

In a high hazard situation, backflow protection is critical to prevent contaminants from entering potable water supplies. Among the options presented, a dual check valve is not suitable for high hazard backflow prevention.

Dual check valves may provide some level of backflow protection; however, they are typically designed for low hazard applications. This is because dual checks do not provide the same level of reliability and fail-safe mechanisms as other backflow prevention devices like air gaps, reduced pressure zone (RPZ) assemblies, or even some thermal expansion tanks.

An air gap serves as a physical separation between the water supply and potential contaminants, effectively eliminating the risk of backflow in high hazard situations. Similarly, an RPZ is designed to handle high hazard applications by using a pressure differential to prevent backflow, ensuring that any harmful substances do not contaminate the drinking water. Thermal expansion tanks are used to manage expanded water due to heating and do not directly provide backflow protection, but they can help maintain system integrity in conjunction with other protective measures.

Thus, in settings identified as high hazard, relying solely on a dual check for backflow prevention would not meet safety standards, making it an inappropriate choice compared to the other options available.