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D.D. Williamson & Co. Catastrophic Vessel Failure

Overview

On April 11, 2003, at the D. D. Williamson & Co., Inc. plant in Louisville, Kentucky, a feed tank in the spray dryer area became overpressurized and failed catastrophically. One operator was killed. Approximately 26,000 pounds of aqua ammonia were released. The incident caused extensive damage to the facility and led to community evacuation and shelter-in-place actions.

Incident Snapshot

Field Value
Facility / Company D. D. Williamson & Co., Inc.
Location Louisville, Kentucky
Incident Date 2003-04-11
Investigation Status Final investigation report approved by the Board on March 12, 2004, at a public meeting in Louisville.
Accident Type Process vessel overpressurization and catastrophic failure; release of aqueous ammonia
Final Report Release Date 2004-03-12

What Happened

  • On the day shift on April 10, 2003, operators completed processing one dried product and began preparing the spray dryer system for the next product.
  • Operators filled feed tank #1 with caramel color liquid and maltodextrin carrying agent and heated the tank to 160°F.
  • The night-shift lead operator arrived at approximately 6:30 pm and the second spray dryer operator arrived at approximately 7:00 pm.
  • At approximately 10:00 pm, the two operators reassembled the spray dryer system and began spray drying material fed from tank #1.
  • They also began preparing the next batch of material in tank #2.
  • At approximately 12:30 - 1:00 am, operators filled feed tank #2 with caramel liquid, water, and maltodextrin.
  • At approximately 1:15 am, operators called the plant manager/supervisor regarding relabeling boxes.
  • At approximately 1:15 - 2:05 am, operators relabeled boxes while heating feed tank #2.
  • At approximately 1:45 - 2:00 am, operators began heating feed tank #2.
  • At approximately 2:00 am, the second operator observed caramel color running out of the agitator shaft seal at the top of tank #2 and down the sides.
  • As they discussed the situation, one of the tank insulation retaining bands snapped.
  • At approximately 2:09 am, the second operator left the area to locate the maintenance mechanic.
  • At approximately 2:10 am, tank #2 exploded.
  • The explosion killed the lead operator and caused the tank to strike the aqua ammonia storage tank and the spray dryer structure.

Facility and Process Context

  • DDW used the vessel in the manufacture of food-grade caramel coloring.
  • The vessel functioned as a feed tank for a spray dryer that produced powdered colorants.
  • DDW produces caramel color by two methods: Maillard reaction and Caramelization reaction.
  • DDW distributes approximately 85 percent of its product in liquid form; the remaining 15 percent is converted from liquid to powder in a spray dryer.
  • The spray dryer was located 6 feet north of feed tank #2.
  • Corrugated aluminum walls enclosed the spray dryer area, and a concrete block wall separated it from other processing areas of the facility.
  • The aqua ammonia storage tank was one of four tanks located just outside and to the west of the spray dryer area.
  • The plant runs 24 hours/day, 7 days/week; operators work 12-hour shifts.
  • The Louisville facility had been in operation since 1948 and employed approximately 45 people.
  • The plant was located in a mixed industrial and residential neighborhood, 1.5 miles east of downtown Louisville.
  • The two feed tanks had been built for use at other D. D. Williamson facilities not in Kentucky and were brought to Kentucky.
  • The feed tanks were operated as pressure vessels with approximately 20 to 25 psi of air pressure added to help push each batch to the spray dryer feed pump.
  • The feed tanks had internal stainless-steel coils and a 1-inch vent line with a manual valve.
  • The plant air system ran at about 125 psi and the steam pressure was 130 psi.
  • The feed tank steam coils were designed with a test pressure of 50 psi.
  • The tanks were never certified by appropriate inspectors when built and were never registered with the National Board of Boiler and Pressure Vessel Inspectors.
  • DDW did not inform the Commonwealth of Kentucky that it was bringing the vessels into the State.

Consequences

  • Fatalities: 1 operator was killed. The lead operator’s death was caused by massive trauma.
  • Injuries: No injuries were reported in the area of the ammonia release. The other four men working at the plant at the time of the incident were not injured.
  • Environmental release: Approximately 26,000 pounds of aqua ammonia was released. The tank contained approximately 30,000 pounds (4,800 gallons) of aqua ammonia at the time of the incident. A vacuum truck recovered almost 4,000 pounds following the incident, indicating a loss of 26,000 pounds, equivalent to approximately 7,500 pounds of pure ammonia.
  • Facility damage: The explosion damaged the western end of the facility. The five-story-tall spray dryer was toppled. The spray dryer area at the west end of the site was totally destroyed. A concrete block wall collapsed. The top head of the feed tank separated at the weld seam and was propelled approximately 100 yards to the west. The shell split open in a roughly vertical line. The aqua ammonia storage tank was knocked off its foundation and piping was ripped loose. A 6-inch gas line ruptured. Debris was scattered up to 150 yards from the source of the explosion.
  • Operational impact: Twenty-six residents were evacuated. 1,500 people were sheltered in place. The Fire Department evacuated two blocks of Payne Street closest to the facility. Residents were allowed to return to their homes at 9:00 am. The plant’s automatic alarm system had already notified the DDW alarm service, which contacted the Louisville Fire Department. Employees turned off the steam, shut down the plant boilers, and isolated the area.

Key Findings

Immediate Causes

  • The feed tank most likely failed as a result of overheating the caramel color liquid, which generated excessive pressure.
  • Plugging of the vessel vent valve.
  • The tank had no overpressure protection.
  • The vessel failed catastrophically because it had no capability to release excess pressure.
  • The one-inch vent line on the feed tank was plugged with hardened caramel.

Contributing Factors

  • The operators did not notice that the temperature of feed tank #2 had risen above the specified 160°F.
  • There were no temperature alarms to warn of overheating and no temperature interlocks to automatically shut down the steam addition.
  • It is possible that while heating up the batch, the operators also put air pressure on the feed tank to provide sufficient force to move the high-viscosity material to the spray dryer feed pump.
  • The operators observed caramel liquid leaking from the agitator shaft seal at the top of the feed tank, which indicated excess temperature and pressure on the tank.
  • It is likely that the caramel liquid also flowed into the 1-inch vent line, filling and plugging it.
  • A tank insulation-retaining band snapped, indicating that the tank shell most likely expanded in response to increased pressure.
  • The 1-inch valve on the vent line was most likely closed as the caramel liquid heated.
  • As the mixture overheated, expanding and emitting steam and vapor, material filled and plugged the vent line, blocking pressure relief.
  • The lead operator most likely opened the vent line valve but to no effect.
  • The feed tank steam coils were designed with a test pressure of 50 psi, but they were exposed to the full plant steam pressure of 130 psi.
  • The plant air pressure was 125 psi, greater than the maximum allowable pressure of the feed tanks.
  • The plant steam pressure was 130 psi, also greater than the maximum allowable pressure of the feed tanks.
  • The feed tanks were installed for use in the spray dryer process without a review of their design versus system requirements.
  • Safety valves on the spray dryer feed tanks had been removed to transport the tanks to Louisville and were never reinstalled.
  • Controlled heating was manual.
  • The operators relied on their experience and attentiveness to ensure that proper temperature was met and maintained.
  • The operators had little guidance on how to control the equipment or on what actions to take in the event of unusual occurrences.
  • The operators were working on relabeling boxes while heating Feed Tank Number 2.
  • The lead operator slept for a few hours at the beginning of his shift, which the report says was a fairly normal occurrence and had no causal relationship to the incident.

Organizational and Systemic Factors

  • DDW did not have effective programs in place to determine if equipment and processes met basic process and plant engineering requirements.
  • DDW had no program for evaluating vessel fitness for service and no management system for evaluating the effect of equipment changes on safety.
  • DDW did not have adequate hazard evaluation systems or procedures for the feed tank system.
  • DDW did not effectively use its consultants and contractors to evaluate and respond to the risks associated with the feed tanks.
  • DDW 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.
  • DDW staff did not consider the two feed tanks to be pressure vessels, even though vessel drawings identified them as such and air pressure was added to help push each batch to the spray dryer.
  • DDW did not notify the Commonwealth of Kentucky that it was bringing the two tanks into the State, as required by Kentucky boiler and pressure vessel regulations, nor did DDW register the tanks with the State.
  • DDW did not consider the feed tanks to be pressure vessels.
  • DDW did not notify the State when the feed tanks were brought into Kentucky, nor did it identify the tanks as pressure vessels for insurance purposes.
  • DDW was not required to reinspect the feed tanks.
  • DDW used contract engineering services and relied on insurance audits, but these inspections and services did not note the use of the feed tanks as pressure vessels.
  • There was no program to evaluate necessary layers of protection on the spray dryer feed tanks.
  • There was no recognition of the need to provide process control and alarm instrumentation on the two feed tanks.
  • Reliance on a single local temperature indicator that must be read by operators is insufficient.
  • The batch sheets contained no safety information, warnings, or guidance concerning operation of the equipment or steps to take in unusual situations.
  • Management was aware of these temperature excursions, but took no actions to modify operating procedures or to install automatic controls or alarms.
  • At DDW, a new operator was paired with an experienced operator to learn the required job assignments.
  • Safety meetings were held to explain general safety concepts, such as fire safety, hazard communication, and emergency plans.
  • On the night of the incident, the lead operator with 5 years experience was teamed with a new operator hired 3 months earlier.

Failed Safeguards or Barrier Breakdowns

  • The tank that failed had no relief device for overpressure protection.
  • The tank had no basic process control or alarm instrumentation to prevent process upsets.
  • There were no temperature alarms to warn of overheating.
  • There were no temperature interlocks to automatically shut down the steam addition.
  • There were no alarms in the feed tank system to alert operators of abnormal conditions.
  • There were no interlocks to automatically shut down the feed tank portion of the spray dryer system if safe operating limits were exceeded.
  • There were no overpressure protection devices in the form of relief valves or rupture disks.
  • The feed tanks had no safety valves or rupture disks.
  • Each tank was equipped with a 1-inch vent line, terminating in a manual valve, which operators used to relieve pressure.
  • The vent valve was intended to be kept open at all times, except when pressure was added to a feed tank for pumping into the spray dryer.
  • The batch sheets contained no safety information, warnings, or guidance concerning operation of the equipment or steps to take in unusual situations.
  • There was no program for evaluating vessel fitness for service.
  • There was no management system for evaluating the effect of equipment changes on safety.
  • There was no program to evaluate necessary layers of protection on the spray dryer feed tanks.
  • There was no recognition of the need to provide process control and alarm instrumentation on the two feed tanks.
  • There was no evidence that DDW conducted engineering reviews when the feed tanks were installed or modified.
  • The steam pressure should have been regulated to a level below the maximum coil design pressure.
  • The coils should have been protected from failure of the steam regulators.
  • The plant air compressor surge tank did not have overpressure protection.
  • The set pressure specified for the installed relief valve was at or slightly below the discharge pressure of the air compressor.
  • The relief valve, whose discharge was not vented to a safe location, could open at any time.

Recommendations

  1. 2003-11-I-KY-R1 | Recipient: D. D. Williamson & Co., Inc. | Status: Not specified | Institute procedures to ensure that pressure vessels are designed, fabricated, and operated according to applicable codes and standards.
  2. 2003-11-I-KY-R2 | Recipient: D. D. Williamson & Co., Inc. | Status: Not specified | Audit all vessels at all D. D. Williamson facilities and ensure that they are equipped with adequate overpressure protection, as warranted; equipped with alarms or interlocks, as warranted.
  3. 2003-11-I-KY-R3 | Recipient: D. D. Williamson & Co., Inc. | Status: Not specified | Implement a program to review existing equipment when it is used for new purposes and when safety devices are removed or altered.
  4. 2003-11-I-KY-R4 | Recipient: D. D. Williamson & Co., Inc. | Status: Not specified | Implement a hazard evaluation procedure to determine the potential for catastrophic incidents and necessary safeguards.
  5. 2003-11-I-KY-R5 | Recipient: D. D. Williamson & Co., Inc. | Status: Not specified | Audit manual control of process conditions, such as temperature and pressure, and determine if safeguards are needed.
  6. 2003-11-I-KY-R6 | Recipient: D. D. Williamson & Co., Inc. | Status: Not specified | Upgrade written operating procedures and train operators on the revised procedures.
  7. 2003-11-I-KY-R7 | Recipient: Commonwealth of Kentucky | Status: Not specified | Communicate to the owners of pressure vessels, mechanical contractors, engineering consulting companies, and insurance companies doing business in Kentucky that used pressure vessels are not exempt from registration and initial inspection before being placed in service in Kentucky.
  8. 2003-11-I-KY-R8 | Recipient: Mechanical Contractors | Status: Not specified | Communicate to your members that used pressure vessels are not exempt from registration and initial inspection before being placed in service in Kentucky.
  9. 2003-11-I-KY-R9 | Recipient: Risk and Insurance Management Society (RIMS) | Status: Not specified | Communicate the findings of this report to your membership.
  10. 2003-11-I-KY-R10 | Recipient: National Board of Boiler and Pressure Vessel Inspectors | Status: Not specified | Communicate the findings of this report to your membership.

Key Engineering Lessons

  • Used vessels brought into a new service must be reviewed against the actual process conditions and system requirements before use.
  • Pressure vessels require adequate overpressure protection. A manual vent line is not an adequate substitute for relief devices.
  • Manual temperature control without alarms or interlocks is insufficient where overheating can create overpressure.
  • If safety devices are removed for transport or modification, they must be reinstalled or the equipment must be re-evaluated before service.
  • Process hazard evaluation must identify necessary layers of protection, including alarms, interlocks, and relief devices.
  • Relying on operator attentiveness and a single local temperature indicator is insufficient for controlling hazardous batch heating.

Source Notes

  • Priority 1 final report was used to resolve conflicts and establish authoritative wording where available.
  • Priority 4 transcript was used only to supplement narrative details consistent with the final report.
  • All facts are limited to information explicitly stated in the provided source extracts.

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