Inside a poultry transformation and canning plant, an ammonia (NH3) refrigeration leak occurred at 3 pm during works carried out to adapt pipe supports and install a defrost water drain in order to protect pipes carrying toxic refrigerant.
The emergency response took place in the pallet loading workshop, along a corridor running alongside the storage chamber. A prevention plan and hot work permit were established beforehand with the subcontractor. Just before installing rivets while working in a basket 4 m aboveground, a non-refrigeration specialist perforated the aluminium insulation (typical thickness: 8-9 cm) on an NH3 pipe in front of the cold storage room entrance. Feeling the resistance and anticipating the presence of ice, he drilled to a depth of 1 cm and struck the pipeline. The liquid NH3 leak at the boundary of the pallet loading workshop led to the evacuation of workshop staff; a few minutes later, the site suspended its activities. The technician descended quickly from the basket without injury and no victims were reported.
Shortly thereafter, plant workers insulated the punctured pipe by closing valves (liquid / hot gas inlet lines), cutting off suction, extinguishing the deep-freezing tunnels, and then opening a suction valve until the pump-down was completed. The subcontracted refrigeration specialist assigned to monitor installations arrived at 4 pm; 3 hours were needed to drain the damaged pipe (15 kg of NH3), by suctioning residual NH3, and to repair it temporarily (tapping / installation of a temporary screw). The liquid NH3 that spread into the drain under the pipe was recovered in a 200-litre barrel. The installation was set to atmospheric pressure (i.e. cessation of pumping-down) the next day, and a properly certified coppersmith plugged the leak orifice using a tack weld. The repair was verified and the installation restarted at 11:30 am.
As it occurred, the technician perforated the pipe at the level of an elbow. Also, 2 NH3 pipes instead of one were running side by side within the insulation, which was not very thick therefore at this particular spot. Several preventive / corrective measures were adopted following this accident, namely:
- for all works, write-up of a precise set of specifications, to be validated by safety and maintenance personnel as well as the assigned subcontractor. A checklist was drawn up to help generate these specifications;
- visual inspection when installing insulation to verify the presence of lining all along the pipeline. According to the plant operator, the practice of placing 2 pipelines at this spot, which explains the lack of lining, no longer exists;
- prohibition of any insulation perforation;
- replacement of all NH3 mask cartridges;
- improved access to the valve station;
- removal of stationary drain supports on the insulation in favour of their fastening to the plant buildings.
