Fire in a fired heater of an ethylene plant

An explosion of a mixture of hydrogen and hydrocarbons occurred at a fired heater of an ethylene unit of a chemical plant. The bad weather caused the shut down of the boiler units. This shutdown decreased the supply of steam and water to an ethylene unit at the facility. As designed, a safety system automatically shut the fired heater down due to insufficient steam and water flow. However, the fuel isolation valve failed to close. Without any flow through the tubes to remove heat from their walls, the tubes in the fired heater reached excessively high temperatures and some of them ruptured, likely due to short-term overheating. Hydrocarbons downstream from the fired heater were released through the broken tubes and ignited by the burner flames inside the firebox, causing a fire.
The post incident investigation determined that the fuel isolation valve could close as designed. The conclusion was that valve did not close due to frozen water from the air supply had frozen or ice formation on the external actuator components.

Source: CBS
[Note of the HIAD validator: for events triggered by the same storm, see previous #1167, occurred at a different plant, and #1056, which affected a pipeline providing hydrogen to the plants.]

The INITIATING CAUSE was due to failure to close the valve providing fuel to the heaters, which then over-heated the tubes causing the release and ignition of the flammable mixture contained in them.
The IGNITION was provide by the heater flames
CONTRIBUTION and ROOT CAUSES were inadequate winterization of multiple valves, instruments, and control systems.

process valve, heater tube

Extreme cold weather from a winter storm caused several freeze-related operational issues.

This event is very similar to the previous one #1167, which happened at another plan of the same company. The both occurred at the same time as the event #1056, affecting a pipeline. They all were triggered by the same extreme environmental conditions caused by a winter storm and by the measures adopted by the plans operators to face lack of feedstock supply. They happened at approximately 100 miles distance from each others.
According to CBS, to the material or component failures characterising these incidents contributed an inadequate preparation of multiple valves, instruments, and control systems to extreme weather conditions.