Texas Utilities concrete stack collapse

On November 14, 1993, a 600-foot concrete stack collapsed onto a coal-fired electric power plant killing one person and injuring four others. The incident occurred at a Texas Utilities plant near Mt. Pleasant, Texas while the facility was shut down for maintenance. Extensive damage occurred within the plant resulting in an extended outage. Destroyed in the incident were a 750 MW generator, a steam boiler, compressor, two 

This tragedy emphasizes the importance of safe work practices especially for situations that have not previously been encountered. A contingency plan should have been drawn up to address the possibility of the solid mass releasing from the wall. Complacency, inexperience, and desire to get the job done may have overshadowed the need to develop safe work procedures. 

The design of the stack was inadequate for the service especially since the scrubbing process introduced solid material into the stack. A good structural or mechanical design does not necessarily ensure suitability for process conditions. The stack should have been reinforced and should have been equipped with some means of minimizing deposits within the inner liner. 

The stack was constructed of an inner liner of hrick shrouded hy a concrete outer shell constructed of reinforced steel and concrete. The hrick and mortar liner had no reinforcing steel to support the assembly from side loading. The concrete shroud was primarily for protection against wind. A space of a few feet existed between the wall of the brick liner and the outer concrete shroud. The brick wall was about 3 to 4 feet thick at the bottom, and the wall thickness lessened with height. The concrete portion was of a similar design. 

A large buildup of fly ash and other material had accumulated on the stack wall opposite the breech where the duct entered the stack. It was formed by solid particulate material in the flue gases impinging on and sticking to the stack wall due to the momentum of the particles in the fast moving flue gas. This buildup was estimated to be up to 15 feet thick at the center and 30 to 40 feet in diameter. 

---