Here’s What Happened:

A tank in this 55 year old facility that produces caramel coloring exploded, killing one worker and heavily damaging other equipment. Vessel fragments were thrown as far as 150 yards/130 meters and the top head of the vessel was propelled 100 yards/90 meters. Shell fragments damaged adjacent structures and equipment including an aqua ammonia tank. This resulted in the release of 26,000 pounds/12,000 kg of aqua ammonia, causing nearby residents to be evacuated or told to shelter in place. Other major damage included collapsed concrete block walls, destruction of the spray dryer area as shown in the photograph, and the rupture of a 6 inch natural gas line. Fortunately, automatic shut-off valves in the gas line prevented a major gas release.

How Did This Happen?

The explosion was a simple case of over-pressurization.

The contents of the feed tank were overheated by steam coils, causing the vapor pressure to rise. There were no temperature alarms or interlocks to automatically stop the steam flow or notify operations that there was a problem. Because the operators were distracted by having to re-label a previously packaged order, they did not notice that the temperature in the tank had risen above specifications. At the same time the temperature was rising, the operators closed a vent line and opened an air pressurization line to the tank in an effort to “blow out” high viscous material. That act completely blocked in the vessel which had no emergency relief system. The result-catastrophic failure to relieve the pressure.

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