Explosion in a steel factory

Workers were performing demolition on a disused furnace. While removing a 10 inch valve from a pipe used to supply coke gas fuel to the furnace, a flammable mixture was unexpectedly released. The flammable material consisted of methane, hydrogen, carbon monoxide and solid coke.
The blast occurred when gas from the line came into contact with heaters which have open flames to keep nearby equipment from freezing.

The workers were not aware that there might be flammable material still in the pipe.
The accident resulted in the death of two workers and 5 others were injured. The two workers that died were working on a platform about 20 feet above the ground and did not have means to escape the fire.

The INITIATING CAUSE of the fire was the release of flammable substances from the a line under maintenance.
The IGNITION SOURE was provided by nearby open flames.
Root CAUSE was the inadequacy of the management systems for the supervision, planning, and execution of maintenance work.
A contributing CAUSE was the absence of a program to identify and address hazards during decommissioning and demolition operations (The workers were not aware of the possible presence of flammable material still in the pipe, and an effective purge was clearly not performed).

furnace, heater

Workers were performing demolition on a disused furnace. Heaters with open flame were used. While removing a 25 cm diameter valve from a pipe used to supply coke gas fuel to the furnace, flammable liquid was unexpectedly released and ignited.

A security perimeter was set up by fire fighters / authorities. The road, as well as the parallel roads,
was cut in both ways of traffic. A diversion was organized.
Fire brigades quickly mastered the fire. They also verified the state of gas cylinders. Those not leaking were cooled, those leaking were left burning in a controlled way. The evolution of the fire was followed by a thermography (thermal camera). It was estimated that the fire burned at a temperature superior to 2000°C.
The following morning, several bottles had finished burning, four were still closed and two others remained wedged under the truck. Fire brigades continued to splash the cylinders with water to cool them, before being able to analyse the situation more in detail. One day later, the fire was totally under control by fire brigades, further hazards involving cylinders were excluded, and the operations of clearing were able to begin. Three days later, the crisis unit met and decided to open again a part of the road in the traffic in both ways. The traffic was disrupted during approximately one week because of renovation work.

Although the intervention was eventually successful, there have been several challenges during the emergency and the report presents some lack of details which hinder the assessment of the intervention:
a) The fire brigade could not know the effect of the mechanical impact on the integrity of the tubes. Also, they could not assess the effect of the heat radiation on them.
b) There is scarcity of water supply along the highway. Nevertheless, because of the possibility of tube over- pressurisation due to exposure to fire, it was decided to make intensive use of water.
c) It took hours for the transport company engineers to arrive on site, due to the traffic jam created by the interruption of the traffic,
d) When they arrived, also they could not provide any certainty at that time whether it was safe to recover the tubes.
e) The report stated that “As soon as the flow of hydrogen had stopped, the tubes were inspected”. It is unclear how it was decided that the risk was terminated. Were they hearing the hissing of the leaking hydrogen? If true, how to explain the presence of a fire, and at the same time the release of un-ignited hydrogen?

The CSB issued the following recommendations to the plant operator:

1. Implement a work authorization program that requires higher levels of management review, approval, and oversight for jobs that present higher levels of risk, such as opening lines potentially containing flammable liquids where there is no low point drain.

2. Monitor the accumulation and flammability of COG condensate throughout the mill and address potentially hazardous changes
3. Survey the mill for dead legs and implement a program for resolving the hazards. Develop guidance for plant personnel on the risks of dead legs and their prevention. Include dead legs in plant winterization planning

4. Provide drains at low points in piping to allow for the safe draining of potentially flammable material.

6. Establish procedures to ensure that insulation is replaced when removed for maintenance.

7 Conduct periodic audits of work authorization, line and equipment opening, dead leg management programs, and decommissioning and demolition activities and share findings with the workforce.

8. Revise the Material Safety Data Sheet (MSDS) for COG condensate to highlight the potential flammability hazard.

9. Ensure that management trains employees and informs contractors with regard to the potential presence of flammable liquids when working with or opening COG condensate piping and equipment.