Explosion in a Chemical Plant, Caused by Accidental Formation of Hydrogen
In a chemical plant, a violent explosion took place during the batch production of chlobenzorex from an aqueous solution of sodium borohydride contained in a feed tank on a movable truck. The workshop was devastated: roof ripped out, light walls displaced, solvent pipes ruptured by the projections. The feed tank was destroyed but the remaining process equipment was not damaged.Outside the workshop but near a door, a technician was projected against the containers by the shock wave. He sustained injuries on the ribs and was hospitalised for a month.DETAILED ACCIDENT SEQUENCEThe sodium borohydride solution (44 kg of powder for 130 kg of solution) was prepared 2 hours before production in a closed 630 litre agitated feed tank. Since dissolving was problematic, the operating mode had been recently modified to include pre-heating of the solution by hot water surface flow (45- 55C). 14:00 The reactor was placed under nitrogen circulation (N2) and connected to the feed tank whose heating was stopped. 14.15 The N2 inlet of the feed tank was connected to the supply hose. 14:20 The N2 supply to the feed tank started with the partial opening of the supply valves of the reactor and the valves at the bottom of the feed tank (at a flow rate of 100 l/h P(N2) = 2.8 bar). 14:40 The N2 hose supplying the feed tank was abruptly torn out letting the gas escape though the opening. The superfluous staff was evacuated from the workshop and an emergency team installed a valve on the N2 inlet to stop the leak. The team tried to decompress the feed tank in the reactor by opening the reactor valve to the maximum and opening the feed tank valve that was difficult to access. At this moment, the feed tanks manhole gave in a few seconds before it exploded.
Event Date
September 2, 1996
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
Post-accident investigations revealed thermal decomposition of sodium borohydride triggered by an excessively high storage temperature (50 C due to hot water surface flow). Maintaining the temperature at 50 C stabilized the decomposition rate in such a way that the small quantities of hydrogen (H2) formed could escape via the leaking feed tank. When the heating was stopped, the reaction evolved in a self-sustaining mode: temperature and pressure increased under the effect of heat resulting from the decomposition, causing a thermal explosion. The inspection hole opened under a pressure of 15 to 20 bar followed by the rupture of the feed tank. The depressurization of H2 in the form of a shock wave was responsible for the damage caused in the workshop.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
Tank with an aqueous solution of sodium borohydride
Storage/Process Medium
Location Type
Location description
Industrial Area
Lessons Learned
Lessons Learned
The following general causes are at the basis of the accident:Poor knowledge of the properties of hydride Absence of a critical analysis of the process and of the effect of its modifications (management of changes) Failing of considering typical production incidents.
Event Nature
Emergency Action
The superfluous staff was evacuated from the workshop and an emergency team installed a valve on the N2 inlet to stop the leak. The team tired to decompress the feed tank in the reactor by opening the reactor valve to the maximum and then opening the feed tank valve that was difficult to access. At this moment, the feed tanks manhole gave in a few seconds before it exploded.
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
ARIA data base
event no. 9841