In a LNG terminal, a pipe supplying a foam generator broke during a manual purging operation of an LNG network. The gas detection system initiated an emergency shutdown sequence without decompression (the terminal was shut down). A fire pump started in accordance with the detection/action matrix. The fire pump’s starting sequence did continue to completion and remained blocked in the 2nd part of the auto-transfo start sequence. This resulted in an increase in the pressure of the fire water network (16 bar).

Consequences

A branch connection on the underground network made of GRL (Glass Resin Laminate) became detached and caused a water leak. A leak was also detected on another foam generator. Several foam generators were in fact unavailable.

Measures taken

After having isolated the leaks, the operator conducted a leak test on the network and, apart from the unavailability of these foam generators, the fire network was in normal operating condition.

Causal analysis

According to the operator, the accident analysis pointed to a malfunction related to an electrical lockout problem. In normal operation, the second start-up phase by auto-transfo lasts only 2 to 3 seconds. On the day of the event, it got stuck at this stage. A sequencing modification is to be performed so that a backpressure valve is released from the 2nd start sequence by auto-transfo whereas currently it is actually released at the 3rd sequence.

The animation of the fire pump on the industrial control system (SCI/SCADA/HMI) also indicated that it had stopped although it was actually running.