Hazard Assessment and Protection Selection
The assessment process
Protection selection follows a repeatable sequence: identify every cross-connection, classify the hazard, determine which backflow mechanisms are possible, then choose the minimum device that fully addresses both. Skipping a step produces the wrong device, which is the most common exam trap.
Classifying hazards
Health hazards (contaminants) include sewage, chemicals, medical waste, pesticides, and process water in food and beverage facilities. Non-health hazards (pollutants) include taste, odor, or color sources such as some heating systems and non-toxic dyes. Degree of hazard is not about how likely a backflow event is; it is about the severity of the consequence if it happens.
Choosing protection
- Air gap where practical, especially for high-hazard, high-volume connections.
- RP for health hazards with possible backpressure or both mechanisms.
- PVB or SVB for health hazards with backsiphonage only, where permitted.
- DC for non-health hazards with backpressure possible.
- AVB, hose bibb, or faucet vacuum breaker at point of use for backsiphonage only.
Traps
- Selecting a device based on pipe size instead of hazard.
- Treating a boiler feed as non-hazard when treatment chemicals are present.
- Forgetting that irrigation systems with chemical injection are health hazards.
- Missing that a fire sprinkler system with antifreeze or a booster pump may need an RP rather than a DC.
Rule of thumb
Write the hazard class and the possible mechanisms on paper before selecting. If the device cannot address both mechanisms, it is the wrong device.
Worked example
An irrigation system has a chemical injector and a booster pump. The injector makes it a health hazard; the pump makes backpressure possible. Therefore the correct protection is an RP assembly, not a PVB.