Which type of backflow preventer is typically used for high-hazard applications?

The type of backflow preventer that is typically used for high-hazard applications is the reduced pressure zone device. This device is specifically designed to protect against backflow risks that can potentially introduce harmful contaminants into the drinking water supply.

Reduced pressure zone devices operate by maintaining a lower pressure in the area between two independently acting check valves. This design ensures that if the second check valve fails, there is a pressure drop that prevents backflow into the potable water system. Moreover, the presence of an air gap in the device further enhances its ability to prevent contamination, making it particularly suitable for situations where the risk of harmful substances entering the water supply is significant.

In contrast, other options, such as atmospheric vacuum breakers and dual check valves, are typically employed in lower-risk applications. Atmospheric vacuum breakers are designed to prevent back siphonage in non-pressure situations and are generally used for less hazardous applications. Similarly, double check valve assemblies are effective for moderate hazard applications but do not provide the same level of protection as reduced pressure zone devices, particularly when it comes to high-hazard scenarios. Hence, the reduced pressure zone device stands out as the optimal choice for high-hazard situations due to its robust protective features.