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NH3 Leak Detector Alarm Response (25 ppm Warning to 500 ppm Evacuation)

Likely causes

Flange gasket aging or loose bolts → micro-leakage reaches 25 ppm

Check: Check flange bolt torque (vs design spec) + apply soap solution and check for bubbling

What to do: 1. Wearing SCBA, cross-tighten flange bolts (80% then 100% of design torque, repeat twice) 2. If gasket damaged, recover refrigerant then replace 3. Use NH3-rated spiral-wound gasket

Pressure gauge / thermometer connection (screwed fitting) seal damaged

Check: Hold NH3 detector within 5cm of fitting and check for ppm reading increase

What to do: 1. Recover refrigerant, then reassemble with PTFE tape + NH3-rated sealant 2. Recheck with soap solution after restart 3. If same location leaks 3+ times, upgrade to stainless welded connection

Piping weld crack or joint corrosion → NH3 gas escaping

Check: Visual inspection (crack lines, rust marks) + nitrogen pressure test (hold 10 bar for 30 min) + soap bubble check

What to do: 1. Fully recover refrigerant, then purge piping section with nitrogen 2. Weld crack: grind out, re-weld with TIG/argon (stainless or carbon steel, NH3-rated) 3. Corroded pipe: replace that section, reinstall insulation, then restart

Safety valve seat damaged → continuous minor leakage below setpoint

Check: Hold NH3 detector at safety valve discharge outlet — sustained ppm rise during normal operation confirms seat damage

What to do: 1. Isolate and replace safety valve (no field repair; NH3 safety valves require full factory calibration) 2. Temporary before replacement: minimize isolation valve opening upstream, run ventilation at maximum 3. After replacement, document setpoint pressure

Machine room ventilation fan stopped → NH3 concentration accumulates (insufficient airflow)

Check: Check fan power and inverter trip status → check NH3 detector reading inside machine room (normal operation: below 10 ppm)

What to do: 1. Before fan recovery, wear SCBA and partially open machine room door (open opposite window simultaneously if possible) 2. Fix motor burnout or inverter trip cause, then restart 3. Reconfirm NH3 detector-ventilation fan interlock (detector alarm → automatic fan at maximum)

Detector sensor end-of-life (electrochemical sensor replacement interval: 2~3 years) → false alarm or missed alarm

Check: Check calibration date + test with standard NH3 gas (25 ppm) → replace if response deviates by more than ±5 ppm

What to do: 1. Replace electrochemical sensor (same model or compatible certified sensor) 2. After replacement, calibrate with 25 ppm standard gas → reconfirm alarm setpoints 3. Record replacement in maintenance log (date, sensor LOT number, technician)

Field tip

NH3 25 ppm = detectable pungent odor. 500 ppm = life-threatening after 30 min exposure. Never rely on smell alone — always trust the detector reading.

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