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 had 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. [Note of the HIAD validator: for events triggered by the same storm, see previous #1167, occurred at a different plant (in this case the fired heaters were properly shutdown, but a tubes failed due to thermal shock, 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. In absence of internal flow, the tubes over-heated, rupture and released a flammable mixture. 

The post-incident investigation determined that the fuel isolation valve could close as designed, but did not close because water from the air supply had frozen or ice formed on the external actuator components.  

The IGNITION was provide by the heater flames.

 CONTRIBUTION and ROOT CAUSES were inadequate preparation for the winter of multiple valves, instruments, and control systems.

heat exchanger

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.