Premises Isolation and Hazard Assessment
Containment vs. internal protection
Premises isolation (containment) protects the public main at the service connection. Internal protection protects fixtures and points of use inside the building. A complete program often uses both. Candidates must know when containment alone is insufficient (e.g., high-hazard internal processes) and when internal protection is required by plumbing code.
Hazard assessment method
Assess each connection by hazard type (health vs. non-health), flow direction (backsiphonage, backpressure, both), probability, and consequence. Identify cross-connections at hose bibs, boilers, irrigation, chemical injection, food service, laboratories, medical equipment, and cooling towers. Classify as high hazard (toxic, infectious) or low hazard (aesthetic, non-health).
Traps
- Assuming a containment device protects internal fixtures from internal backflow.
- Misclassifying a chemical injection system as low hazard.
- Forgetting temporary connections (hoses, tank filling).
- Ignoring elevation and pressure changes that create backsiphonage.
Worked example
A hospital has a boiler, laboratory, and irrigation. Containment at the meter may be an RPZ, but internal protection is still needed at laboratory sinks (air gap or PVB) and boiler feed (RPZ). The assessment lists each point, hazard, and device.
Rule of thumb
High hazard + backpressure = air gap or RPZ. Low hazard + backsiphonage = double check or PVB. Document the reasoning for each point.