Anhydrous Ammonia Leak in a Cold-Storage Compressor Room
A cold-storage facility uses 1,500 kg of anhydrous ammonia in a compressor room. At 06:40 the fixed detection system alarms at 150 ppm at the compressor skid; the room is normally unoccupied. A maintenance technician is found near the door complaining of eye irritation and coughing; five other workers are in the loading dock 25 m downwind. The emergency shutdown has not been activated. The facility has two self-contained breathing apparatus sets, one ammonia-rated suit, and no written pre-emergency plan. Wind is 3 m/s toward the loading dock. The technician wants to go back in to close a manual valve because the automatic isolation valve has failed open. The local emergency responders are 15 minutes away.
1. What are the immediate rescue and exposure-control priorities?
Read the worked answer
Reasoning: Ammonia is a corrosive, toxic gas with a strong odor and irritant effects; 150 ppm at the skid is already above common occupational exposure limits, and concentrations near the failed valve may be much higher. The technician is symptomatic and should not re-enter.
Priorities: move the technician to fresh air without entering the plume; flush irritated eyes with water for at least 15 minutes if exposure is suspected; call medical responders and tell them ammonia exposure. Evacuate the loading dock workers upwind and account for all six people. Activate the emergency shutdown from outside the room if the control is accessible and labeled. Establish hot, warm, and cold zones; monitor ammonia at the perimeter; deny entry. Notify the fire department and plant management. Use water fog only from a protected position to knock down vapor and protect exposures; do not direct water into liquid ammonia. Only trained responders in SCBA and ammonia-rated chemical protective clothing should attempt isolation.
2. Evaluate the technician's proposal to re-enter and close the manual valve.
Read the worked answer
Reasoning: The proposal is an uncontrolled rescue-by-repair. The automatic isolation valve has failed open, the source is not isolated, and the technician is already symptomatic. One ammonia-rated suit and two SCBA sets are not enough for a solo entry without a standby team, monitoring, and a rescue plan. The facility has no written pre-emergency plan, which makes the entry even less defensible.
Decision: deny the entry. The manual valve should be closed only by a trained emergency response team with SCBA, ammonia-rated suits, a buddy, atmospheric monitoring, and a standby rescue crew. If the valve can be operated remotely or by a fixed emergency shutdown, use that instead. The automatic valve failure should be treated as a mechanical-integrity and management-of-change issue. Meanwhile, evacuate and isolate, protect the loading dock, and let the fire department or a contracted hazmat team handle the isolation. Re-entry to 'just close the valve' is exactly the kind of judgment error that turns a release into a fatality.
3. What should happen before the facility restarts and before the technician returns to work?
Read the worked answer
Reasoning: Restart requires proof that the leak is controlled and that the safety systems that failed are restored. The technician's return to work requires medical clearance and evidence that the response system will not expose him again.
Before restart: repair or replace the failed automatic isolation valve; pressure-test the system; verify ammonia detection and alarm calibration; restore ventilation; confirm emergency shutdown is accessible from outside; update the pre-emergency plan with local responders; provide ammonia response equipment and training; conduct a drill; complete a management-of-change review. Inspect for corrosion or mechanical damage at the compressor skid and document the repair.
Before the technician returns: medical evaluation and clearance; fit testing and training if he is expected to use respiratory protection; clear instructions that no one enters an ammonia plume without the full response team. Also review staffing, alarm response, and evacuation routes. Document the incident and corrective actions, and verify local reporting requirements for the release and the injury.