At a chemical plant, 3 kg of methyl ethyl ketone (MEK) were discharged through the safety valve on a reactor following a pressure rise (to 50 mbar) inside the reactor. Solvent vapours escaped via the vents and spread both in the unit and outdoors on site premises. Upon noticing the odour, technicians checked all reactors in the zone and remarked that the temperature of one of them had reached 91°C, far surpassing the recommended 50°C. The heating circui t was closed and the cooling system activated.

The accident occurred after loading raw material (MEK and 1,4-dioxane) at the time of setting heating conditions : the position of the temperature regulation loop in manual mode while the regulation valve remained open caused the excessive heating. Noncompliance with control instructions when beginning to heat the reactor was specifically cited. Moreover, the very high temperature alarm threshold had been set at 150°C and temperature rea dings were not being recorded.

The measures adopted subsequent to this accident focused on: introducing controls and monitoring procedures for batch reactor heating, improving the modification tracking procedure used in safety reviews (regarding alarm thresholds) ; accepting completed works; and verifying alarm thresholds during temperature indicator calibration.