Failed Premise Isolation Assembly in a Mixed-Use Building
A six-storey mixed-use building has a 100 mm reduced-pressure-principle (RPZ) backflow assembly serving as premise isolation in the basement mechanical room. Downstream users include a ground-floor dental clinic with three operatories and a vacuum/evacuation system, a second-floor restaurant with a carbonator and a pre-rinse spray, a wet-pipe sprinkler system fed from the domestic main, eight irrigation zones, and a boiler plant dosed with nitrite/molybdate treatment chemicals. Floors three to six are apartments. The annual test was performed yesterday: with the downstream isolation valve closed, the first check leaked steadily under reverse pressure and the relief valve failed to reseat after opening. The owner produces a plumber's invoice from last year showing the same first check was 'adjusted'. The water utility requires written notification of any failed premise isolation assembly within 24 hours. The restaurant is booked for a 200-guest event on Saturday.
1. What must you do in the next 24 hours, and what are your legitimate options for keeping water on to the building?
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Treat the assembly as failed and out of service. A first check that leaks under reverse pressure means the premise is unprotected: a main break or a nearby hydrant draw can pull boiler chemicals or dental waste backward into the public main. Close the upstream and downstream isolation valves and lock/tag the assembly.
Notify in writing within 24 h - the owner and the utility, attaching the test report with the actual readings. Do not file a passing report.
Repair properly. Fit an OEM repair kit for that make and model (seats, discs, springs, relief valve internals) or replace the assembly. Last year's 'adjustment' is not a repair - a damaged first-check seat cannot be tuned back into compliance, which is exactly why it failed again.
Interim supply, ranked: same-day repair and retest; swap in a spare certified assembly of adequate size; feed the building through a temporary RPZ or a temporary connection protected by a physical air gap. Last resort is to keep the building shut down. Never remove the check, gut the internals, install a bypass, or leave the assembly in service 'until Saturday' - the event is a scheduling problem, not a justification for a cross-connection.
2. Classify the hazard of each downstream use and explain whether the premise isolation assembly alone is adequate protection.
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Premise isolation protects the mains; it does not protect the building's own occupants. Internal pressure drops (a hydrant draw, a sprinkler activation, a main break) can siphon contaminants back into the building's potable piping.
Hazard ranking:
- High: dental clinic - blood, saliva and amalgam at the cuspidors and chair-side vacuum/evacuation lines, which sit below the rim of the bowl and are frequently submerged. Carbonator at the restaurant - CO₂ creates backpressure, not just backsiphonage. Boiler make-up - nitrite/molybdate chemicals, with possible higher system pressure. Irrigation - fertilizers, soil, ponding water and submerged heads.
- Minor/moderate: apartment fixtures and the restaurant's domestic fixtures with properly air-gapped or vacuum-broken connections.
Therefore: provide individual protection at each high-hazard connection - an air gap or an RPZ on the dental vacuum water supply, RPZ on the boiler make-up (air gap preferred), a double check or RPZ on the carbonator supply as the local code allows, PVB/RPZ on irrigation, and hose-vacuum breakers on all threaded outlets. The premise RPZ then acts as the final barrier rather than the only one, and any single internal failure does not become a contamination event.
3. The owner asks you to bypass the assembly for the weekend and reinstall it Monday 'so nobody loses money'. How do you answer, and what do you put on paper?
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Refuse, and put the refusal and the reason in writing before you leave the site.
The reasoning to give the owner:
- Legal exposure. A bypass is a prohibited cross-connection. If the utility or an inspector finds it, the water service can be discontinued, and the owner plus the contractor can face fines. Your tester certification and any licence depend on filing accurate reports - a report that says the assembly is in service when it is bypassed is a false report.
- Liability. If backflow reaches the main and contaminates the distribution system, the cost and the health consequences fall on the party who created the connection. That is not a weekend-sized risk.
- Insurance. The owner's policy and yours generally exclude knowingly created code violations.
On paper: a short work order note stating the assembly was tagged out of service, the date/time, the utility notification, the readings, the options offered (same-day repair, replacement, temporary RPZ, temporary air-gapped supply) and the owner's instruction. Have it acknowledged.
Then solve the real problem: bring the repair kit or a spare assembly on site the same day. Most RPZ failures are fixed in a few hours; the weekend event is almost always solvable by repair rather than by bypass.