In a plant making starch by-products, 2 starch dust explosions occurred at 1:47 pm inside the facility’s multi-product shop dedicated to manufacturing extra-dried modified starches. The shop was partially shut down while awaiting a specialist subcontractor. Technicians placed the building in safe operating mode using the pushbutton circuit-breaker, steam injection stop button and nitrogen blanketing of the dryers and cookers. About ten employees had to be evacuated from the building, while in-house responders extinguished the fire sparked by the explosions. External responders were not notified.
A subcontractor had been welding a coupling onto a pipe at the time of the blasts. According to the plant operator, as the hot work permit was being prepared, the circuit undergoing maintenance was shut down and the 2 valves hooked up to the bagging line and elevator closed. The foreman on duty had asked the subcontractor to complete the work permit in the control room, but this instruction was ignored prior to the welding step. Under normal operations, the valve feeding the elevator was open and welding particles entered the pipe, supplying the elevator and igniting the fire at its base. Next, the fire spread via the pipe network to the rectangular sieve, reaching the sieve waste bin and, due to a pressure loss, to the circular sieve where the explosions took place. The plant operator also indicated that the workshop’s state of cleanliness prevented any ensuing explosion inside the building.
Only property damage was reported; a section of the siding blown off by the blast was reinstalled, as were the explosion hatches; also, the sieve gratings were replaced and the facilities cleaned. The idle shop equipment plus the presence of a hatch or hood on some of the machines (assembly hopper, sieve at the humidifier outlet) mitigated the consequences of these explosions.
Five days later, the inspection authorities for classified facilities issued the following observations:
– Regarding emergency response organisation and for hot spot works in particular: after close assessment of log records (authorisation and hot works permit), there were serious breaches in both the preparation and execution of this response, failure to lock out essential equipment (elevator feed valve), insufficient exchanges between the subcontractor and site technicians.
– As regards guaranteeing installations’ structural integrity prior to restart: portions of shop equipment were subjected to the effects of explosions as well as fire. Even though damage appeared to be limited, the operator still had to verify that the affected facilities, including those dedicated to safety, were compliant or restored to compliance in their original condition. The operator was required to submit to the inspectorate a file containing warranties of equipment integrity before restarting the shop.
– Regarding the risk analysis and experience feedback: during normal operations, the consequences of an explosion could have been worse given the large quantity of starch in the circuits. Since the electrostatic risk or risk of hot surfaces resulting from equipment malfunctions could no longer be excluded, the inspectorate requested a detailed risk analysis for the entire shop.
– As for the zoning classification tied to explosive atmospheres and equipment compliance: the installation diagram, with indications of zones prone to explosive atmospheres, provided to the inspectorate revealed inconsistencies, knowing that this identification was indeed critical to ensuring a high level of safety for machines installed in the various zones. The inspectorate thus requested the operator to commission an independent appraisal to validate compliance in the determination of such zones.
Furthermore, the inspectorate suggested that the Prefect adopt an emergency measure order for the first two points above and another order for the last two.
