Hydrogen fire in a solvents production plant

A hydrogen jet fire from a pipe was detected by a night operator making rounds in a solvent production unit.
The unit's emergency response team managed the fire in minutes. Operators stopped the flow of hydrogen by closing a valve. The hydrogen network was purged with nitrogen.
The unit has three reactors, out of which only one was in operation at the time of the incident. The gaseous effluents from each of the reactors, mainly consisting of hydrogen, were collected via a network of vents and discharged to the atmosphere via a set of hydraulic valves.

On the day of the incident, a section of the workshop was completely emptied for maintenance and inspection. The hydrogen leaving the reactor in operation passed through this section which presented fewer obstacles (all equipment had been purged and valves remained open) than the hydraulic valve set of the vent network. At the outlet of the section, the hydrogen escaped to the atmosphere through a pipe which was not free of impurities. The hydrogen flow brought engulfed solid particles with the consequence electrostatic discharge as a result of their friction against the pipe walls. This ignited the hydrogen. In addition, the pipe had been drained the day before, but the solid particles were not be removed by water.

The INITIATING CAUSE was the accidental release of hydrogen during maintenance.

This happened because one unit out of the three production units was shut down and depressurised, and the hydrogen sent to the vent from the other two units still operative found a quicker path through the depressurised unit, instead of being safety released via the vent.
The risk analysis did not predict a return of hydrogen to a section through the vent system.

Therefore, the ROOT CAUSE can be attributed to a shortcoming of the design of the venting system, and possible to lack of procedural steps aiming at completely isolating the units under maintenance from the rest of the system.

exhaust pipe, solvent reactors

fire

Following this accident, the UIC (Union of Chemical Industries) advocated the following:

When multiple sections are connected to common facilities, identify all deviations, and their consequences, that may occur on either side of the element in common. In particular, it is necessary to study the situation where the operating conditions are stable on one side, and on the other hand, the operating conditions are transient, such as stopping and starting equipment;
when an incident scenario of this type is identified, modify the operating instructions of the unit to include the closing operation of the corresponding valves.

The risk analysis did not predict a return of hydrogen to a section through the vent system. Following this accident, the UIC (Union of Chemical Industries) advocated:
(1) When multiple sections are connected to common facilities, identify all deviations, and their consequences, that may occur on either side of the element in common. In particular, it is necessary to study the situation where the operating conditions are stable on one side, and on the other hand, the operating conditions are transient, such as stopping and starting equipment.
(2) When an incident scenario of this type is identified, modify the operating instructions of the unit to include the closing operation of the corresponding valves.