One Monday at around 5:00 a.m., a fire was detected on an anodizing line in a surface treatment shop while the other lines were being started up. The technician present in the shop alerted the firefighters. A team of 50 firefighters arrived to extinguish the fire. The firewater, which was diluted with sulphuric acid from a tank that was damaged by the flames, was contained in the bunding. An anodic oxidation tank melted.
The fire started when the heating elements immersed in two plastic tubs were switched on. The tubs had been emptied by a maintenance technician before the weekend so that maintenance could be performed on them. The extraction duct above the tanks sucked the hot gases upwards, explaining the vertical extension and fanning of the fire. The technician thought she had turned off the circuit breaker supplying the heating elements before leaving for the weekend, but the survey report indicated that the circuit breaker was in fact on. It also stated that the circuit breakers were not arranged inside the panel in the order of their numbering and that their functions were not clearly identified. In addition, the circuit breakers were not locked out using the appropriate toggles and padlocks but rather with adhesive tape and cable ties, inducing other technicians to believe that a circuit breaker had inadvertently tripped and then reset it.
The survey report also stated that the wiring of the relay control used to prevent the heating element turning on when the level in the tub is very low was reversed compared with the electrical diagram at the level switch output. As a result, when the level in the tub is very low, the relay is energised, supplying power to the contactor on the heating elements’ power circuit and sending a correct level signal to the PLC, which then turns on the heating elements.
In agreement with the surveyors of the operator’s insurance company, all the bath heating elements were replaced by hot water exchangers. The survey report recommended that the operator be more rigorous when locking out and tagging out equipment.
