Created on July 7, 2017

An incident occurred when operations personnel were preparing equipment for maintenance work by de-inventorying and draining vessels located between two isolation points.

A single block valve isolated the vessels being decontaminated from a pressurized and inventoried depropanizer column containing hydrocarbons; unknown to operations personnel, the valve leaked in the closed position, resulting in backflow of flammable material from the depropanizer.

When an operator opened the vessel drain valve to empty what he assumed was condensate water from the vessel to the oil water sewer, the hydrocarbons from the depropanizer also released to the sewer and ignited, resulting in a flash fire.

Prior to maintenance work, operations personnel commonly prepare equipment by depressurizing, de-inventorying, washing, and draining. These activities often involve opening process equipment and piping and can result in a release of hazardous energy. Though equipment preparation activities can occur rather frequently in process plants, the tasks involved may vary among pieces of equipment and piping and combinations of equipment and, thus, may be non-routine and not be included in an existing procedure. Because of the non-routine nature of equipment preparation activities, process plants should develop a system to ensure that equipment preparation activities are carefully planned, which includes selecting proper isolation methods and identifying hazards through a risk assessment.

Key Lessons :

  1. Operational tasks that involve preparing equipment for maintenance can be uncommon and non-routine; therefore, ensure procedures include steps for preparing all process equipment for maintenance.
  2. For all equipment preparation activities, develop a process that requires pre-planning and hazard identification prior to initiating the work, which includes assessing hazards that may be introduced and steps for mitigating those hazards.
  3. When isolating equipment for de-inventorying or decontaminating activities prior to maintenance work, avoid relying on single block valves, even when the valves are newly installed, to control the release of hazardous energy.
  4. When an equipment preparation task or isolation plan needs to be modified or expanded due to leaking valves or changing conditions, initiate a process to evaluate hazards that may be introduced by the change.
  5. Avoid draining materials containing, or potentially containing, hydrocarbon or flammables into the sewer or other systems not specifically designed for such services, especially when ignition sources are present.

Dedi Irawan, ST, SFS
Process Safety Engineer

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