A thunderstorm occurs near a deposit of flammable liquids protected by a lightning conductor with a primer (PDA). The indirect effects of the lightning damage one of the 4 interface cards of the computer. This card was interfaced with the bus network repatriating high level security alarms from the depot tanks. The operator detects the malfunction by means of the depot supervision indicating the communication fault. The operator does not have a back-up card and cannot replace it quickly. He informs all operating personnel and requests increased vigilance when monitoring the rate sheets. Operations continue for 5 days before the computer interface card is actually replaced.

All the security alarms at 4 of the company’s 6 depots located within a radius of a few kilometres are retransmitted on a supervision computer to the operators’ offices, so that they are warned by an audible signal when an alarm is triggered at one of the 4 sites and informed by a view of the site indicating on the supervision computer what type of alarm has been triggered. These alarms are repatriated either by modem using the wired network, or by a hertzian radio communication system or by a wired link via a protocol. The high level alarms of the tanks, the detection of liquid hydrocarbons in the retention basins and the fire detection of the electrical rooms are thus retransmitted. The supervision computer has 4 interface cards connected in a short wired link with modems, converters, interfaces with the above-mentioned networks or buses. It is supplied with 220 V mono uninterruptible power supply. The modem connection is made via the telephone distribution frame. The alarms transmitted to the supervision computer are sent back to the operator by the autocom via a dialling box to his mobile phone. The damaged card was not protected against the indirect effects of lightning.

Following this incident, the operator kept an additional card as a back-up and implemented the recommendations of the study on the indirect effects of lightning carried out in April 2006, consisting of protection, mainly by means of lightning arresters, the supervision computer, the alarm grouping centres, sensors and technical premises, the fire pumps of 3 depots, the generator set of 2 sites and the “barrel hall” extinguishing system of one of them.