An April 11, 2003, vessel explosion at the D.D. Williamson & Co., Inc. (DDW), plant in Louisville, Kentucky, killed one operator. The explosion damaged the western end of the facility and released 26,000 pounds of aqua ammonia (29.4 percent ammonia solution in water), forcing the evacuation of as many as 26 residents and requiring 1,500 people to shelter-in-place.

DDW used the vessel in the manufacture of food-grade caramel coloring. It functioned as a feed tank for a spray dryer that produced powdered colorants. The feed tank, which was heated with steam and pressurized with air, was operated manually. To ensure that the filling, heating, and material transfer processes stayed within operating limits, operators relied on their experience and on readouts from local temperature and pressure indicators.

The feed tank most likely failed as a result of overheating the caramel color liquid, which generated excessive pressure. .

KEY ISSUES:
• OVERPRESSURE PROTECTION
• HAZARD EVALUATION SYSTEMS
• LAYERS OF PROTECTION
• OPERATING PROCEDURES & TRAINING

ROOT CAUSES:
1. D.D. Williamson did not have effective programs in place to determine if equipment and processes met basic process and plant engineering requirements.
2. D.D. Williamson did not have adequate hazard analysis systems to identify feed tank hazards, nor did it effectively use contractors and consultants to evaluate and respond to associated risks.
3. D.D. Williamson did not have adequate operating procedures or adequate training programs to ensure that operators were aware of the risks of allowing the spray dryer feed tanks to overheat and knew how to respond appropriately.

Image Credit: CSB