Sulfuric Acid Tanker Explosion Due to Unintended Hydrogen Production
To repair a corroded flange on a 4500 liter sulfuric acid bowser outlet pipe, an angle grinder was being used to prepare the surface for welding. Within a few seconds of starting work there was a bang and an eruption of white, or grey-yellow, smoke from the outlet pipe. The injured person (IP), who was angle grinding the pipe at the time, suffered deep burns to his right inner thigh. The IP was wearing shorts at the time of the incident. It appears the tanker had been used exclusively for the movement of 77% sulfuric Acid in the past. It had been open to air for about 3 or 4 weeks before the incident. The tank was opened at high and low level by opening pipe flanges.
Event Date
September 19, 2001
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
A plausible direct cause for incident appears to be ignition of hydrogen within the tank by the heat, or sparks, from the angle grinder. Root cause is related to the documented risk of hydrogen build-up within concentrated sulfuric acid vessels. Ingress of atmospheric moisture dilutes the acid and initiates acid attack on the steel. Hydrogen is liberated from this reaction and can accumulate to form a flammable atmosphere within the vessel.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
sulfuric acid tank, maintenance work
Storage/Process Medium
Storage/Process Quantity
4500
Location Type
Location description
Industrial Area
Operational Condition
Pre-event Summary
The accident occurred during repairing a corroded flange. A grinder was used to prepare the surface for welding.
Lessons Learned
Lessons Learned
The absence of any detailed forensic examination of the scene, and physical evidence, makes it impossible to be certain of the cause of the incident.Since the lack of the required ventilation has been identified as possible root cause. a specific recommendations is made. For improved tank purging systems, and the introduction of a permit-to-work system.
Event Nature
Emergency Action
Emergency action taken is not stated
Emergency Evaluation
Ventilation of the vessel would be hampered by the internal baffles and small area of the ventilation openings.
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Event description provided by HSE, original source confidential