Explosion in a Cold Rolling Plant
Employees were trying to open the manhole cover (600 mm diameter) of a hydrofluoric acid tank with a grinder, when an explosion occurred. The explosion was probably caused by the presence of hydrogen formed by the acid attack of the metal. At the moment of the accident, the tank was empty, but uncleaned, and separated from the filling and ventilation pipes.According to the eMARS report (see references), in the course of cleaning work on the hydrofluoric acid storage tank, the residual of concentrated hydrofluoric acid remaining in the tank was diluted with water and not completely neutralized with sodium hydroxide. Subsequently, the container was sealed, after which the cleaning work was interrupted for at least two days. During this time, an explosive atmosphere formed in the tank, as a result of the reaction of the dilute hydrofluoric acid with the iron material of the container which produced hydrogen. When the cleaning work resumed, the explosive mixture was ignited presumably by the sparking due to the work with an angle grinder.
Event Date
May 5, 2010
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
The immediate cause was the ignition of the accidentally formed hydrogen insider the tank.A possible root cause of the accident would be the lack of risk assessment related to the potential formation of explosive atmosphere in the tank. Inadequate neutralization of the residual acid and the disconnection of the tank from the venting line were contributing causes.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
hydrofluoric acid tank
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
Maintenance works were executed on an empty hydrofluoric acid tank. Hydrofluoric acid is a solution of hydrogen fluoride in water.
Currency
Lessons Learned
Lessons Learned
According to the eMARS report (see References), the corrective action was to provide suction to prevent the formation of an explosive atmosphere inside the containers. Maintenance would then take place with the exhaust air switched on.More in general, an adequate risk assessment need to be performed in all cases aiming at assessing the adequacy of measures such as inertization of the tank before maintenance, explosive gaseous mixture detection, and safety training.
Event Nature
Emergency Action
The on-site firefighters evacuated the employees and secured the site.
Release Type
Release Substance
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
RP ONLINE News, 5 Mai 2010 (in German),
https://rp-online.de/nrw/staedte/krefeld/thyssen-kessel-deckel-erschlae…
(accessed October 2020)
Event description in the European database eMARS
https://emars.jrc.ec.europa.eu/en/eMARS/accident/view/19179a7d-a997-157…
(accessed October 2020)