Hydrogen formation and explosion at a steel making plant

NOTE: one of the source of this event attribute the explosion to the recombination of oxygen and hydrogen formed by thermolysis. However, the classic reaction products in the case of molten metal reacting with water are metal oxides and hydrogen. The second source mention only the steam produced by the molten steel. This and similar event needs to be carefully discussed among EHSP members before drawing hard conclusion on the role of hydrogen and steam.

The explosion occurred at the electric melting furnace of the steelworks. The furnace for melting the steel was equipped with 4 heat exchangers to cool 2 electrodes and the 2 doors with water. The continuous water circulation was controlled for all heat exchangers via a single manually operated valve. An improper, excessive level of molten steel resulted in a direct contact between the metal and the heat exchanger, resulting in a leak on the heat exchanger wall. Contact between the molten steel and the water resulted in explosive vaporization and decomposition to form hydrogen (plus metal oxidation). As a result, an explosion occurred.

Such low-impact events occur regularly in the plant (on average once a year) when floating slag comes into contact with the heat exchanger. The plant operators are used to such events that cause a characteristic noise. They usually stop the water circulation and drain the furnace as quickly as possible. When the familiar noise was heard, the plant operator in charge evacuated other employees and attempted to stop the water supply. But a massive development of steam prevented him from reaching the manually operated valve before the explosion occurred.
After the explosion, the fire department and medical helpers were called. 10 slightly injured employees were taken to hospital for evaluation, but were all released on the same day. The smelting furnace, other parts of the plant and the building were severely damaged. The plant was shut down for several weeks.

The INITIATING CAUSE was accidental water thermolysis. The unusually high level of molten steel which created the conditions for this to happen could not be clarified.
The use of unsuitable valves in an unsuitable location was considered a cause contributing to the accidental sequence. Moreover, the plant operator's safety instructions were inadequate, and the assessment of the risks at the start of the accidental sequence underestimated the explosive potential.

electric melting furnace, heat exchanger

Low-impact events of the type occurred in this incident occurred regularly in the plant (on average once a year), caused by floating slag entering into contact with the heat exchanger. The plant operators were used to such events that cause a characteristic noise. They usually stopped the water circulation and drain the furnace as quickly as possible.

10 slightly injured employees were taken to hospital for evaluation, but were all released on the same day. The smelting furnace, other parts of the plant and the building were severely damaged. The plant was shut down for several weeks.

EMERGENCY MEASURES INSIDE THE PLANT:
The operator initiated the emergency shut-down and venting system of the hydrocracker unit, and evacuating the control room.
The on-site emergency procedure was activated, implying the shut-down of the entire refinery, the evacuation of non-essential personnel, the mobilization of the refinery fire brigade and the call on-site of engineering management staff.
The refinery fire fighting installation was quickly brought into use.

EMERGENCY MEASURES OUTSIDE THE PLANT:
Road blocks were set up. Workers in neighbouring factories were asked to inspect their sites for damages. It was not necessary to evacuate houses.

Re-approval of the system was required, following a review and a new design of the number, type and location of the valves to control water circulation.