Explosion in Electrostatic Precipitator During Maintenance, Worker Injured
An explosion occurred in an electrostatic precipitator whilst it was being accessed for maintenance. The explosion caused an inspection hatch cover, which had been unbolted, to be blown off and created a fireball which engulfed an electrician causing minor injuries. The sequencing of the shutdown tasks was fundamentally flawed as the spades were introduced immediately prior to the opening up of the vessel, after the 1.5 day steam purge and 3.5h cooling period. Leakage past the inlet gate valves would allow a flammable atmosphere to develop as the main constituents of coke oven gas are hydrogen, methane, carbon monoxide etc. The exact source of ignition cannot be established, the probable source was pyrophoric deposits in the vessel.
Event Date
November 10, 1998
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
Immediate cause: probably leakage of the combustible gas mixture (hydrogen, methane, carbon monoxide) ignited by pyrophoric deposits.Root cause: mistakes in the maintenance procedure, specifically lack of gas detection step.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
Electrostatic precipitator of a coking plant
Storage/Process Medium
Location Type
Location description
Industrial Area
Operational Condition
Pre-event Summary
The facility was under maintenance.
Currency
Lessons Learned
Lessons Learned
The inspection report identified the following deficiencies:The company had two types of generic procedures. A)Working instructions (for high risk and complex activities,)B)Working Procedures (describing what the operator is required to do.)The only company document for work on an electrostatic precipitator was a set of Working Instructions. 1.The section on 'Taking a unit off plant' only detailed what the process operator was required to do before handing it over to the maintenance department. 2.No reference was made to introducing the spades. 3.A further flaw in the system was that no test for a flammable atmosphere was undertaken prior to entry. It was acknowledged that the vessel was a confined space as a daily permit was required for entry, which required an atmosphere test, by a site chemist.
Event Nature
Emergency Action
Unknown
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Event description provided by HSE, original source confidential