Fire in the Isomerization Unit of the Refinery
The accident originated in the isomerisation unit and propagated to the benzene saturation unit. The accident source was a mechanical rupture of one of the two compressors used to transfer hydrogen mixtures to the isomerisation unit . The rupture caused the release of a gas mixture containing hydrogen, which ignited by mixing with air, forming a jet fire. The jet fire headed was directed towards the adjacent benzene saturation unit, hitting a pressure vessel located 14 m from the release point (the jet flame could have been 30 m long in absence of obstacle). The weakening of this vessel caused the release benzene which contributed to extend the fire. Off-site fire brigade teams intervened extinguishing the fire within approximately 1 hour and a half of work. No damage was reported to persons or to the environment.
Event Date
December 27, 2002
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
According to the eMARS report (see references), the rupture was probably caused by a failure of the crank mechanism made of piston rod and the drive shaft. The latter may have caused a collision of the piston on the cylinder-bottom of the compressor.The combined effect of the collision and of the operating pressure may have caused the failure of the nuts holding the cylinder bottom; a second energy release threw the cylinder, which was bottom weighing 100 kg, approximately 14 meters away.According to the declarations of the operator, a mechanical interference between cylinder bottom and drive shaft was the possible initiating event. The nuts holding the failed cylinder bottom showed completely abraded threads. On the contrary, the bolts were practically undamaged and just slightly blackened.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
hydrogen compressor , benzene saturation unit
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
The hydrogen compressor where the accident started was a reciprocating compressor operating in a pressure range of 15 to 21 bars. The maximum amount of substances registered in the plant inventory are 25,000 m3 of hydrogen rich gas mixture out of which 1,500 m3 of pure hydrogen, and 147000 tons of liquid automotive petrol.
Consequences
Number of Injured Persons
1
Currency
Lessons Learned
Lessons Learned
According to the eMARS report (see references), the company adopted the following measures based on the experience gained and the studies carried out company:A) Measures related to structures and equipment: a1) replacement of the reciprocating compressors with a centrifugal compressor; a2) Replacement of the old, manually driven shut-off valves with electrically driven valves at the intake near the compressor, to minimize gas leakage;a3) More strategic placing of the hydrants and fixed detectors.B) Measure concerning management and documentation aspects:b1) Better location of personal protective equipment;b2) Better training (including frequent drills) of personnel in management of emergencies; systematic call-up ofb3) Clear sequence of operations to secure the equipment;b4) Updated risk analysis for the safety report;
Event Nature
Emergency Action
15:00 - A loud abnormal noise coming from the isomerisation unit was heard by the personnel working near that unit. Having identified the in the compressor the cause of the noise, they tried to stop it via the emergency shut-off switch. In the control room the emergency shut-down procedure was activated, triggering the a rapid depressurisation by blowing down the system.Immediately afterwards a violent release of a hydrogen rich gas mixture occurred from the compressor bottom, the jet ignited almost instantly and hit the adjoining part of the benzene saturation unit.The refinery personnel closed the manual valves installed on the pipe mains and started to extinguish the fire, activating the fixed cooling systems and the foaming system of the units involved and nearby units.15:03 - the onsite Emergency Control Centre team gathered and established communication with the Advanced Control Centre. 15:12 - Off-site fire brigade alerted. Meanwhile the on-site emergency response team fought the fire with a fixed and mobile extinguishing units from all sides. 15:16 - Emergency shut-down procedure started for the entire establishment. 15:30 - First off-site fire brigade team on-site, supporting response operations.15:50 The size of the fire greatly reduced by because the compression section of the plant no longer fed the fire; fire continued in the benzene unit engulfing it with flames. 16:25 the fire almost extinguished; cooling operations continued. 16:50 the emergency called off.
Emergency Evaluation
The accident could have caused more severe damage without the adoption of effective response measures and the joint effort of the on-site personnel and the off-site fire brigades; even if the on-site emergency response organisation could be improved.
Release Type
Release Substance
Release Amount (kg)
300.00
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Flame Type
Source Category
References
References
Event description in the European database eMARS
https://emars.jrc.ec.europa.eu/en/emars/accident/view/8bb6d0cc-dd21-292…
(accessed October 2020)