Hydrogen Fire at a Chemical Plant
The fire broke out in the acid etching tank of the ferric chloride manufacturing unit of a SEVESO-classified chemical plant. In this tank, the attack reaction of the iron metal with hydrochloric acid in solution is carried out, which results in ferrous chloride and hydrogen. The hydrogen generated is swept away by a large supply air fan to maintain the gaseous sky of the tank below the LFL. A few days after the accident, the operator opened and analysed the tank to determine the origin of the fire. According to the ARIA report, the start of the fire was caused by a slow combustion of hydrogen, initiated during the loading of metal. Despite the air circulation, hydrogen accumulated at the bottom of the tank due to its overfilling. The fire then spread outside the tank through the roof opening caused by the degradation of the hydrogen detector and by melting the blast doors. The fire was then alimented by the plastic components of the equipment and the surrounding piping, as well as by the oil from the hydraulic pistons of the roof door of the tank.
Event Date
June 15, 2017
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
The immediate cause was the overloading of the tank, which allowed accumulation of hydrogen despite the air circulation system. Considering the corrective actions described in the ARIA report, the root cause was probably inadequate safety design and operation.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
reaction tank, production of iron chloride (FeCl2)
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
The stoichiometric reaction at the basis of the process is: Fe + 2 HCl FeCl2 + H2
Lessons Learned
Lessons Learned
The accident suggests that the operative procedure related to the loading of the materials and the preventive measures (hydrogen detection) were inadequate.According to the ARIA report (see references), the operator updates the risk analysis of this unit and reinforces controls on the level of scrap metal in the tank and analyses of hydrochloric acid.It also added safety features on the low air sweep rate and high temperature in the tank and lowers the alarm threshold of the hydrogen analyser.
Event Nature
Emergency Action
23:40 The Plant safety emergency plan is initiated . 23:53 The fire is reducing00:50 Despite a small residual still persisting, the fire is extinguished and the reaction unit stopped. 00:45 The emergency plan is called off. 01:25 The leak is sopped.
Release Type
Release Substance
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Flame Type
Source Category
References
References
Event description in the French database ARIA
https://www.aria.developpement-durable.gouv.fr/accident/49915/
(accessed September 2020)