During rounds at a chemicals storage facility, a technician observed that the level indicator on a hexane tank read empty, although it should have contained 7,700 litres of this particular flammable and highly volatile hydrocarbon. The computerized inventory report, printed out 2 weeks prior, listed a full tank. The subsequent report, compiled the day before and indicating an “abnormally empty” tank, had either not been read or else gave no grounds for concern. Also, the site’s gas testing meter alarms were tripped twice in the evening two weeks prior (accumulation of hexane vapours?). The on-call supervisor conducted measurements with a portable meter but recorded nothing abnormal during his rounds.

The site operator carried out an acoustic test using nitrogen and found that the pipe connecting the tank to the transfer pump was leaking due to corrosion and moreover that the tank outlet valve was open or leaking. He replaced both the hexane and toluene pipes and advanced the scheduled hydraulic test date for the other pipes, given the ageing installations.

Informed of these events 8 months later, the inspection authorities for classified facilities observed during an on-site visit that the pipe tray heading towards the underground hazardous liquid waste storage tank (drippings) communicated with the storm drain network; the 5.8 tonnes of hexane had thus undoubtedly evaporated, partially into the atmosphere, but also migrated to: the water table 25 m deep, the waste tank, and the natural environment via the storm drain network. The waste tank was pumped and the storage tank outlet valves were verified and repaired as needed. The inspector of classified facilities also noted that inventories were not being updated on a daily basis and the emergency procedure to be enacted for any gas detection on the stationary testing meters had not been formalised (oral instructions only during on-the-job training); they requested additional piezometric monitoring of the water table directly below the site.