Explosion in a metallurgy plant

Explosion within a blast furnace occurred at the plant manufacturing iron.

The event occurred at one of the blast furnace of the plant, which exploded. The explosion was so powerful that the entire furnace, which with its contents weighed approximately 5000 tonnes, raised some 0.75 m from its supporting structures, leading to the explosive release of hot material: the released substances, 200 tonnes in total, consisted in solids, semi-solids, (molten metal) and gases.
The event caused three fatalities, twelve severely injured workers and many more with minor injuries.

The explosion occurred after two days in which it had been attempted to recover the furnace from a chilled-hearth situation caused by cooling water ingress.
The water leak into the furnace also caused an increase in temperature of the molten metal, and the production of hydrogen and oxygen via thermolysis (dissociation of water by heat). The hydrogen detectors gave an increased concentration levels: instead of the usual signal below 2%, during the previous two days the hydrogen detectors reading could exceed 7%. The released gases were mainly carbon monoxide and hydrogen.

The INITIATING CAUSE of the explosion was water and hot molten materials mixing within the lower part of the furnace vessel.
At the origin of this situation was the failure of safety-critical water cooling systems, which cased water entering the furnace.

According to the HSE report (see references), the INTERMEDIATE CAUSES were failures in health and safety management., which were not only confined to the blast furnace plant, but extended elsewhere within the company (in particular to the department supplying cooling water for the furnace). There was insufficient redundancy and security of cooling water supplies, and overall cooling system reliability showed a downward and deteriorating trend over several months.

The ROOT CAUSE was the lack of a suitable and sufficient risk assessments for blast furnace operations, having as a consequence the failure to implement robust technical and procedural controls.

blast furnace, water as coolant

In the two days before the explosion, workers had unsuccessfully attempted to recover the furnace from a chilled-hearth situation caused by cooling water leakage. At the time of the explosion, attempts were continuing to rectify the abnormal operating conditions that this had created and to recover the furnace.

DESCRIPTION OF THE FACILITY
Manufacture of iron in blast furnace and associated generation of blast furnace gas. A detailed description of the facility can be found in the HSE report (see references).

Damage was generally limited to the confines of the blast furnace area. The furnace was beyond repair; was demolished and rebuild.
The lifting of the furnace body caused considerable disruption to all its services and associated plant.
The building steel cladding was severely damaged in several areas, with some sheets being projected in excess of 40 m. Molten slag was thrown over most of the cast house floor and flowed as far as the entrance ramp to an estimated depth of between 300 and 600 mm.

Significant amounts of flame and gas were emitted through the furnace top bleeders, but downstream gas containment was maintained and there was no major blast furnace gas away of the furnace.

The company were prosecuted under the Health and Safety at Work etc. Act 1974 and were fined £1.33m with £1.74m costs

As explained in more details in the HSE report, the main and the corrective actions were:
1. The Safety Department has to be integrated into operational and engineering management.
2. Since the accident, the blast furnaces have been brought under the COMAH regime (Control of Major Accident Hazards Regulations, in place since 1999). In this way, predictive tools for the assessment and management of risk received greater use within the steel industry. Examples of predictive tools are: Hazard and Operability Studies (HAZOPS), Failure Modes and Effects Analysis (FMEA), Fault Tree Analysis (FTA), Process Hazard Review (PHR) and Layers of Protection Analysis (LoPA).
3. AS critical element of the process and its safety, the furnace water supply systems should have an adequate level of reliability built into the system. This reliability should be guaranteed by an adequate level of redundancy and suitable maintenance, and monitored to identify any threats to its integrity.
4. Early detection of water leak is an essential preventive measure. The appropriate instrumentation, specifically designed for leak identification, should be installed to give earlier and more precise detection of leaking elements.
5. There was a lack of knowledge of the changing status of the furnace. Despite the presence of quantitative data on liquid iron levels, hydrogen levels and the evolution of other parameters, a competent senior manager was missing. Nobody was able to overview the developments and interpreting the critical parameters.
Further recommendations were issued for the improvement of the management of emergency (a clear line of responsibility was missing) the design of blast furnaces, and the preparedness of the employees (understanding of the industrial processes, safety training).