Flooding of motor-pump units

At about 3:45 a.m., a technician at an oil depot noticed white smoke and noise coming from the pumping station of the site’s fire protection network. He raised the alert and put on his equipment to enter the pumping station. After evacuating part of the smoke, he noticed that 3 pumps supplying the network were flooded under 1.80 m of water. One of them, which had caused the smoke, was still running. The technician was able to stop this pump. With the help of the site’s internal firefighters, the origin of the flood was identified: a water tank used to boost the fire pumps, had overflowed. The leak was stopped at 4:05 am by closing the supply valve on this storage tank.

The plant’s internal contingency plan was initiated. Only one of the 4 pumps in the fire system, located outside the pumping station, remained operational. Loading and unloading operations at the site were suspended. The 200 m³ of water that flooded the pumping station contained traces of diesel fuel released by the pumps. This water was pumped into a containment basin and treated on site. External firefighters and mobile equipment were required to secure the depot. Loading and unloading operations were able to resume in the morning. Rescue services left the site 4 days later, after the operator had put fixed fire-fighting equipment in place.

The causes of the overflow

The day prior to the event, alignment operations had been performed on the fire protection system. The system was temporarily connected to a tank in order to discharge the water following a hydraulic test. Once the tank was emptied, a technician restored the fire protection system to its standard configuration. He closed the tank’s bottom valve and then opened the bottom valve of the boost canister. Once connected, the storage tank emptied into the fire protection system. The tank then began to fill automatically from the site’s water supply. Once full, the filling did not stop, causing the canister to overflow at 8 p.m. A mechanical blockage is thought to have prevented the float from stopping the filling operation at the high level.

Following the incident, the operator reviewed its operating procedure for emptying a tank after a test. In particular, the valve downstream from the fire system’s discharge valve is closed first, and not the tank’s bottom valve. This is done to prevent the system from being completely drained. The operator also intends to review the security guard’s tasks. From a technical perspective, the operator also plans to:

• resize the pumping station’s drainage pump;
• install leak detection in the station with alarm reporting in the control room;
• reassemble the electrical cabinets;
• review the lighting in the pumping station.