In a pharmaceuticals plant, a rupture disc on a closed glycol water circuit broke, causing discharge of the product.

Subsequent to the incidents of 2008, works were carried out towards the end of the year on the thermal fluid network. The exchanger yielding the thermal fluid from a single fluid had to be disassembled due to a lack of tightness. To pursue this production step, the thermal fluid network was replaced by a direct single-fluid supply; the exchanger was bypassed. Moreover, after encountering reliability problems on the thermal fluid pumps, the 250-litre expansion vessel was replaced by a 2,500-litre vessel protected by a rupture disc calibrated at 4 bar.

During restart of the installations at the beginning of the following year, an abnormally low pressure was recorded on the thermal fluid expansion vessel at night. The leak causing this problem could be located within 30 min; all thermal fluid network modules were immediately turned off. The rupture disc broke at 3.6 bar, leading to a flow on the roof: 10 to 15 m³ of glycol water (40% monoethylene glycol) were discharged into the retention basin via the stormwater drainage network. Upon analysis, 70 m³ of liquid were transferred to the plant’s treatment unit. The expansion vessel was equipped with a PSH (Pressure Safety High) device, which was not activated because the rupture disc had already broke at a pressure below 4 bar.

This incident, combined with a similar one occurring the day before (ARIA 36102), led to polluting the RHINE River (ARIA 35773).

The operator temporarily replaced the rupture disc by a “blind flange” and connected the output of the rupture disc line to the thermal fluid collection tank. The rupture disc would be replaced and calibrated at 5 bar. The operator set up a checkpoint on the roof to more quickly detect this type of incident.