A pressurised autoclave opened around 3:50 pm inside the cooking station of a condiment and seasoning plant. A vapour flow at 70°C and liquid at the same temperature were released, seriously burning the employee operating the device and a co-worker to a more minor extent.

The 2 employees were emptying and cleaning the autoclave basket when one of them, while on the walkway, noticed the adjacent autoclave’s green indicator light showing completion of its production cycle. He then activated the autoclave vent valve before pressing the control box button to open the lid. As the lid unlocked and suddenly opened, he was splashed with the burning mix. The co-worker below the walkway was struck by a small spray. Upon hearing his colleague’s scream, the co-worker proceeded to undress him and place him under the shower. The plant operator shut down the cooking apparatus’ 3 autoclaves. Both employees remained under the shower until first responders arrived 10-15 min later. The employee with serious burns to his back was transported to the Lille Hospital, while his less severely injured but extremely shocked colleague was transferred to the Laon Hospital.

When the employee activated the vent valve, the autoclave cycle had indeed been completed but residual pressure remained. The slightly burned employee remembered seeing vapour exit the vent, thus indicating that the lid was open though the valve had not yet finished discharging the pressure (internal pressure: around 0.1 bar).

Ensuring safe autoclave opening relied on 2 pressure switches: one a contact switch relaying a cue to the programmable controller to authorise opening when pressure dropped below 0.03 bar, the other a membrane switch returning a measurement to the controller and authorising opening at this same pressure. On 24 October, when inspecting the adjacent autoclave, which was identical to the one involved in the accident, the expert noted that the membrane pressure switch setting was not compliant with the supplier’s manual, which indicated a setting of 0.03 bar to trip the opening. The controller’s guideline listed 0.1 bar; upon testing, the pressure switch was found to actually activate at 0.18 bar. Moreover, the operator observed that the contact pressure switch was clogged by meat projected during the operating cycle. This projection had most likely interfered with the pressure measurement. Hence, both switches authorised the autoclave opening: one whose setting deviated from manual prescriptions, the other was fouled leading to an erroneous measurement. Compounding the situation, the employee failed to verify the absence of vapour at the vent valve outlet before opening the lid as well as the absence of pressure by reading the manometer.

A governmental order was issued on 30 November since the plant had not drawn up a proper inventory of its pressure devices. Furthermore, several of these devices had not been tested prior to being placed in service nor recorded at the time.

The operator was required to commission a certified body to evaluate all its vapour generators, autoclaves and pipes, before carrying out the adjustments or replacements deemed necessary. This appraisal, assigned to the inspection for classified facilities in May 2013, noted the absence of user’s instructions in french, plus a manufacturer’s design and/or setting error. A service start-up inspection would have avoided placing the technician and the opening control mechanism so close to the tank and would have verified technicians’ training and the posting of instructions. Such a control step would have also exposed inconsistencies in the user’s guide and the lack of maintenance performed on safety systems.

Following the accident, several actions were planned: revising autoclave use procedures, posting safety instructions, training personnel in pressure equipment risks. A cleaning of all safety devices (pressure switches, vent valves, sensors) and a visual inspection were also scheduled prior to each production run. The preventive maintenance plan was updated by incorporating disassembly of the contact pressure switch once a month.

In 2012, production losses totalled €150,000 while 2013 losses were anticipated to top €400,000.