For the 2nd time in less than 24 hours, the window on an 80-m³ beer tank in a brewery exploded after pressure in the container had risen. Plant activity was suspended for the time needed to determine the precise cause of the accident, deemed rare, though widely known within the brewing industry.
The fermentation process involved 2 phases: a start-up period during which an air/carbon dioxide mix was released into the atmosphere for 10 to 16 hours, depending on the type of beer, followed by fermentation with CO2 recovery lasting 8 days. The tanks, operating at 800 mbar of pressure, held a volume of 1,040 m³, split between 840 m³ of net volume and 200 m³ of dead space occupied by the CO2. Each floor housed 2 pipelines equipped with both a gate valve and check valve, the former 80 mm in size for discharging CO2 into the atmosphere, the latter at 105 mm for recovering CO2, and fitted with a bypass to discharge gas in the event of an incident. The connection from the tank outlet to one of the pipelines by a hose was performed manually and depended on the extent of fermentation. The 26-cm diameter Plexiglas disc, used as an inspection hole, had been screwed onto a metal support 2.8 m above ground. When the accident happened, the tank vent was positioned towards the CO2 atmospheric discharge. As was the case during the previous explosion, 40 m³ of CO2 were dispersed into the atmosphere and a small quantity of beer overflowed into the sewers, making its way to the site’s wastewater treatment plant. The accident occurred during a shift change, but no employees present in the break room were affected. Fire-fighters ventilated the brewery so that activities could resume. The only difference observed with the first accident was the proper operability of the check valve. The window might have burst due to a loss of mechanical strength in the Plexiglas material (weakened when the 1st window opposite had burst earlier, along with ageing of the material whose resistance over time had not been guaranteed) or else to a clogged CO2 discharge for release into the atmosphere (e.g. caused by system impurities, ice).
A series of emergency measures were adopted: all 16 tanks were hooked up to the CO2 recovery pipeline bypass leading to the atmosphere; the pressure of all tanks was manually verified (using a manometer); windows were replaced and inspected; the basement was assigned for personnel and subcontractors; and tank filling operations were suspended. Subsequent to this incident and that of the previous day: all windows were replaced; tanks were equipped with manometers; a “basement entry authorization” procedure was implemented; pipelines for discharging gas to the atmosphere and recirculating gas were inspected; a rupture disc was installed on each tank; and employees were provided with portable CO2 detectors.