In a chemical plant, a leak of a mixture of hydrogen chloride (HCl), vinyl chloride (VCM) and 1,2-dichlororethane (DCE) occurred on a pump. The pump was designed to convey product from the ripeners to the HCl distillation column. The leak occurred on the housing of the hermetic magnetic drive pump. At approximately 10 p.m., the detection sensors located in the northwest storage area’s retention basin detected 22% of the LEL. The sprinkler system and a deluge sprayer were activated. The staff looked for the source of the leak.

At 10:09 p.m., the zone alarm was triggered and the intervention teams were called and initiated the leak containment protocol. At 10:15 p.m., the installations’ output was reduced pending identification of the origin of the leak. At 10:46 p.m., two equipped technicians identified the origin of the leak and then stopped the pump. At 11:15 p.m., the technicians noticed a discrepancy with regard to the position of the shut-off valve on the intake side of the pump and had a doubt as to whether it was completely closed. The manual upstream and downstream valves were closed at 11:19 p.m.

The quantity of HCl-VCM-DCE gas/liquid mixture was estimated at 200 kg of HCl, 700 kg of VCM, and 900 kg of DCE. The quantity remaining in liquid form in the retention basis could not be evaluated.

This incident had no external consequences. The measurements made by observation vehicles around the establishment did not detect the presence of any product. On the platform, the cloud remained confined within the site’s perimeter, with weak detections by the hygiene sensors installed in the vicinity. The aqueous effluents, resulting from the spraying operations, and the liquid organic phase were stored in the retention basin and processed at the facility.

The pump had just been overhauled and had been in place for 4 days. When opened, several cracks were noted on the isolation bowl over a surface area of 110 mm². The magnets of the magnet holder were degraded but not detached. They had rubbed against the external part of the bell to the point of piercing it. A foreign body may have become wedged between the magnets and the bell through the sensor port during assembly/disassembly, during transport or at the workshop.

Based on the findings and assessments conducted, the operator undertook the following actions:

• Technical:
  • Modification of the intervention process on pumps of this type:
    • Mandatory plug on the sensor holder’s hole during disassembly operations, during transport and after repair;
    • Cleaning of the workshop;
    • Protection of the temperature sensor on site.
  • Verification of valve condition, test and overhaul periodicity
• Organisational:
  • Feedback with all the workshop crews.