A cyclohexane (C6H12) leak could be smelled on a pipe coupling temporarily installed on a supply line to the adiponitrile production workshop at a chemical complex. With the alarm sounded, the leak, evaluated at between 4 and 4.5 tonnes, was quickly stopped; however, since it had occurred adjacent to a storm drain manhole, the site’s internal emergency plan was still activated. Due to outside temperatures near 0°C, the cyclohexane solidified (< 6°C) on the ground. On-site response teams verified all sewers in the particular zone using both a gas detector and TOC-meter and then washed out those sections where the product had solidified. No trace of C6H12 was detected at the factory outlet.

This accident, which had no impact on either the workforce or the environment, was initiated at a coupling between 2 flexible pipes used to clean, by blowing nitrogen, unused cyclohexane lines and thus avoid frozen pipes. The system designed for this purpose had been implemented following the accident one year prior that triggered a discharge of 850 to 1,200 m³ of cyclohexane into the soil. Human and organisational errors were the cause of this latest accident; 2 days earlier, the same pipe had been used to blow the cyclohexane line leading to the storage zone. At the end of that day, this line was isolated and the nitrogen intake valve on the pipe closed, though the pipe remained connected despite the procedure calling for its disconnection. Shortly thereafter, the line’s shut-off valve was opened again to allow transferring cyclohexane. Two days hence, the leak was observed.

An analysis of causes indicated that the ring-seal gate on the pipe was damaged upon closing, due to the technician’s use of a pipe wrench. As for the pipe, a vehicle rolling over the coupling undoubtedly caused this leak. While awaiting installation of a new pipe on an electrical tracking rack in order to eliminate any need to bleed the cyclohexane line, several corrective measures were adopted, namely: state-of-the-art reminders regarding removal of an unused pipe; use of a pipe without a coupling while potentially adding a nitrogen frame to reduce pipe length; greater technician awareness of the technologies associated with the various types of valves.