Passing relief valve and a supervisor's instruction to isolate it
At a small arena, an ammonia plant serves the ice pad. On a Friday evening the operator notices frost and a plume at the discharge stack of the high-pressure receiver's relief valve, and a sharp ammonia smell in the machine room. The room detector reads 60 ppm and is climbing slowly. The receiver is a 1.2 m³ vessel with one relief valve, and there is a gate valve in the pipe between the vessel and the relief valve; the gate valve is fully open. Outdoor temperature is -5 °C and the wind is light. The supervisor, on the phone from home, says: 'Close that gate valve to stop the leak, we'll get a contractor in Monday.' The operator is alone, holds a Refrigeration Operator certificate, and has a half-hour of air-line respirator capacity in the plant room.
1. Evaluate the supervisor's instruction. What is wrong with it, and what should happen instead?
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Closing the gate valve would remove overpressure protection from a vessel full of liquid ammonia. The relief valve is the only device standing between that receiver and a rupture if it is isolated, liquid-full and warmed - by ambient heat, by the sun, or by a fire. A 1.2 m³ receiver isolated and liquid-full will hydraulic-lock and fail catastrophically, and no relief device would be left to act.
Under CSA B52-type requirements, a stop valve between a pressure vessel and its relief device is acceptable only in restricted arrangements - typically a three-way cock with two relief valves and a locking device, or a valve locked open. A plain gate valve is a non-conformance that should be reported and corrected.
So: refuse the instruction, and put the refusal in writing with the reason. The defensible action is to lower the pressure and liquid level in the receiver - pump liquid out to another vessel or to the low side if the piping permits - so the leaking valve sees as little liquid as possible, then replace the valve with the section isolated and depressurised, using a certified relief valve of the correct set pressure.
2. What are your immediate protective actions, including entry decisions and evacuation triggers?
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Treat 60 ppm and rising as a live release. Keep out of the room unless you must enter.
Before any entry:
- PPE: ammonia-rated respiratory protection (SCBA or air line with escape bottle), chemical suit, face and eye protection.
- A buddy outside with communications.
- Emergency ventilation running; ignition sources controlled.
- A pre-agreed evacuation trigger - for example the high-alarm set point or a visible plume at the door.
60 ppm is well above the 25 ppm eight-hour occupational limit for ammonia under O. Reg. 833, so the half-hour air supply is a limit on entry time, not a target. Priority tasks: read the detector at the door, use remote shut-off or pump-down to reduce receiver contents, barricade the area and keep the public out of the end of the building where the stack discharges, and keep the wind at your back.
If the leak cannot be reduced remotely, evacuate, call 911, and let trained responders with SCBA make entry. Do not attempt to nurse a live ammonia release alone because it is Friday night.
3. What notification obligations arise, and what must be recorded and corrected?
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Notification: an ammonia release to the environment must be reported without delay to the MECP Spills Action Centre under the Environmental Protection Act; the pressure equipment incident - a leaking relief valve and the non-compliant isolation valve - must be reported to TSSA; and the owner and insurer must be told. Call the fire service if the release cannot be controlled.
Records: log the detector readings and times, the actions taken, the supervisor's instruction and your refusal, the quantity of ammonia lost, the repair details, and the relief valve's capacity, set pressure and certification.
Correction: the relief valve must be replaced with a certified valve set at or below the receiver's MAWP, installed by qualified personnel, with the discharge piped to a safe location and the outlet checked for blockage. The plain gate valve arrangement must be corrected to a compliant dual-relief/three-way arrangement or removed entirely. Until both are done, operate conservatively: keep the receiver level low, watch the detector, and do not rely on that valve for protection.