There was a generalised power cut in a nitrogenous products and fertilizer manufacturing plant following failure (heating) of a 90 kV transformer constantly supplying all facilities of the site. For unknown reasons, the remote switchover to the two emergency transformers by the power company was not successful thus causing the power failure. The turbo-alternator of the site was unavailable during the incident and thus could not replace the emergency power supply. The two 630 kVA and 110 kVA diesel generators started automatically thus securing the facilities and avoiding any equipment damage. A few minutes after the ammonia unit shut down due to “electrical fault”, the operator sounded the mini sirens located in each unit and designed to warn the technicians of an emergency for a limited time period. These uninterruptible mini sirens that operate non-stop for 3 minutes and than are audible in the adjoining areas created confusion around the site causing residents to call the emergency services and town halls thus involving the municipal police, prefecture and the media. The unusual silence in the facilities was undoubtedly why the sirens were heard in the neighbourhood. The operator had to specify the conditions for implementing the automatic relay between transformers, justify the provisions taken to ensure regular preventive curative and maintenance on the turbo-alternator and the diesel generator sets, review the mode of use of mini sirens and their activation/deactivation conditions.