CSB Releases Final Report on D.D. Williamson & Co. Explosion and Ammonia Release

March 18, 2004

In a final report, the U.S. Chemical Safety and Hazard Investigation Board (CSB) said the April 11, 2003, explosion and resulting ammonia release at the D.D. Williamson & Co. plant in Louisville were caused by over-pressurization of an eight-foot-tall food additive processing tank. The CSB said the accident could have been prevented had the company installed an emergency pressure relief valve on the tank. The CSB also noted that the tank that exploded had a history of prior damage.

The explosion took the life of an employee who had worked for five years at the plant. It caused extensive damage to the facility, which makes caramel coloring for use in food products such as soft drinks. The explosion, which occurred around 2:10 a.m., blew the top of the tank some 100 yards to the west. The tank shell struck a nearby ammonia tank, knocking it off its foundation. This resulted in the release of an estimated 26,000 pounds of aqua ammonia (ammonia gas in a water solution) over a five-hour period, forcing the evacuation of 26 residents and requiring 1500 others to remain sheltered in their homes.

Board investigators presented the findings at a public meeting in Louisville, and Board members voted 4-0 to approve their final report. Lead CSB investigator David Heller said, "The accident was avoidable. In the 1980s, the company shipped two used tanks, including the one that exploded, from out of state to the Louisville facility. The tanks had not been inspected, certified, or registered as pressure vessels prior to bringing them into Kentucky — a requirement of the state’s Boiler and Pressure Vessel Safety Act."

Mr. Heller said the company routinely heated liquid caramel in the vessels to 160°F and then used compressed air to help push the caramel out to a dryer. Mr. Heller said, "Since the vessels were operated above pressures of 15 pounds per square inch, the company should have classified these tanks as pressure vessels as required by law. The tanks should have been equipped with emergency pressure relief valves, pressure and temperature alarms, and automatic systems to shut down the process in case of over-pressurization. In the absence of these safety measures, operators had to rely on visual inspection of temperature and pressure gauges to keep the process under control."

Investigators determined that on the night of the incident, two workers, who were brothers, filled the tank with liquid caramel and turned on the heating steam to the vessel. Meanwhile, they were occupied in another room re-labeling some product boxes that had been mislabeled. Returning later to the tank room, the second operator noticed that the caramel was leaking from the top of the vessel and called in the lead operator. A metal insulation band snapped in two as the tank expanded under the increasing temperature and pressure inside. The lead operator then sent his brother to locate a mechanic. Moments later the vessel exploded, killing the lead operator.

Investigators said the lead operator likely had attempted to open the tank’s air vent to release the excess pressure. But the vent was not designed for emergency pressure relief and was not adequately sized for the vessel. In any event, investigators later found that the vent pipe had clogged with solidified caramel product.

The CSB concluded that it was "improbable" — based on the temperature of the heating steam — that the pressure inside the tank ever exceeded 130 pounds per square inch (psi). Drawings show that the tank was built with a maximum working pressure of 40 psi, and CSB investigators estimated that the tank, as originally designed, was probably capable of withstanding pressure up to 180 psi. Therefore, the CSB said, the "more likely cause of failure" was that the tank had been weakened sometime earlier. The report noted that the tank had been deformed on two occasions prior to being installed in Louisville when it was subjected to excessive vacuum, and was subsequently repaired. The repairs were not inspected or certified.

CSB Board Chairman Carolyn Merritt said, "The tragedy that befell this worker is another example of why plant owners and managers must have effective engineering oversight and hazard analysis systems in place. They should be regularly analyzing various scenarios that could lead to accidents and put into place safety systems that result in extra layers of protection."

Investigators cited several root causes, noting that the feed tanks were installed without a review of their design or fitness for service. Investigators concluded that D.D. Williamson & Co. did not have effective programs to determine if equipment and processes met basic engineering requirements. The company also lacked effective systems for assessing the hazards of its processes. Finally, the company did not instruct workers on the hazards of overheating or over-pressurizing the caramel vessels.

The CSB issued several recommendations to the D.D. Williamson & Co.: examine all vessels at company facilities and ensure that each pressure vessel has adequate pressure relief systems and alarms. The CSB also recommended the company upgrade operating procedures, train its operators, and implement a hazard evaluation procedure to determine the potential for catastrophic accidents. The CSB recommended that the Kentucky state government inform pressure vessel owners, mechanical contractors, engineering companies, and insurers that used pressure vessels must be inspected and registered before being placed in service in Kentucky.

The CSB is an independent federal agency charged with investigating industrial chemical accidents. CSB investigations look into all aspects of such events including physical causes such as equipment failure as well as inadequacies in safety management systems. Typically, the investigations involve extensive witness interviews, examination of physical evidence, and chemical and forensic testing. The agency’s five board members are appointed by the president and confirmed by the Senate. There is currently one board vacancy. The Board does not issue citations or fines but does make safety recommendations to plants, industry organizations, labor groups, and regulatory agencies such as OSHA and EPA.

Guidance for Assessing Safety, Health Fixes is Offered by NIOSH

Two new resources are available from the National Institute for Occupational Safety and Health (NIOSH) — a manual and a companion site on the NIOSH web page – to help guide employers in assessing and measuring the effectiveness of steps they have taken to improve occupational safety and health in their workplaces.

In addition, it provides case studies of evaluations of interventions intended to reduce serious work-related injuries in four industries. These case studies were partnerships of employers and employees. They offer further guidance and useful ideas for employers that can be used in other settings. The interventions that were assessed in the case studies addressed the prevention of:

  • Back injuries in nursing homes
  • Strains to employees’ backs, arms, and hands in meat processing
  • Cuts from case-cutting tools in a grocery store chain
  • Exposures to perchloroethylene in drycleaning establishments

Assessments are important for determining if changes were effective in reducing work-related injuries or illnesses, and for assuring that changes do not inadvertently increase other risks as they make an intended improvement.

Using links on the page, readers can go directly to the individual case studies, to suggested steps for evaluating changes, and to forms and surveys that can be used in assessments. A PDF of the manual also can be downloaded.

The manual, DHHS (NIOSH) Publication No. 2004-135, was developed by the Intervention Effectiveness Team under the National Occupational Research Agenda (NORA). The team was formed by representatives from NIOSH, industry, labor, and academia under NORA to foster the growth of intervention evaluation in workplace safety and health. The manual and the web page reflect NIOSH’s goal of translating research findings into practice in workplaces to prevent work-related injuries and illnesses. Printed copies of the manual will be available shortly by calling 1-800-35-NIOSH (1-800-356-4674) 

OSHA Cites Wyman-Gordon for Fork Truck Hazards

Wyman-Gordon Co.'s alleged failure to safeguard workers against fork truck hazards at its North Grafton, Mass., forging plant has resulted in $75,000 in fines from OSHA.

Wyman-Gordon was cited for alleged willful and serious violations of the Occupational Safety and Health Act following an OSHA inspection prompted by an Oct. 10, 2003, accident at its Worcester Street plant. An employee suffered a head injury when the carriage of a fork truck dropped unexpectedly and struck him.

"Allowing fork trucks to operate in an unsafe condition exposes workers to serious injury," said Ronald E. Morin, OSHA's area director for central and western Massachusetts. "Prompt and proper repairs could have prevented this accident. Effective preventive maintenance can minimize similar hazards in the future."

OSHA's inspection found the fork truck had been damaged prior to the accident but had not been removed from service for repairs as required under OSHA standards. In addition, a second fork truck was kept in service for 10 days after workers spotted significant damage and informed management of its need for repairs.

OSHA has issued a "willful" citation to Wyman-Gordon for failing to correct this hazard and proposed a fine of $70,000. OSHA defines a willful violation as one committed with an intentional disregard of, or plain indifference to, the requirements of the Occupational Safety and Health Act and regulations.

Wyman-Gordon was also issued a "serious" citation, with a $5,000 proposed fine, for failing to develop and maintain a preventive maintenance program for fork trucks. Such a program would allow for early identification and repair of defects before they become major safety hazards. OSHA defines a serious violation is one in which there is substantial probability that death or serious physical harm could result from a hazard about which the employer knew or should have known.

Wyman-Gordon has 15 business days from receipt of its citations and proposed penalties to either elect to comply with them, to request and participate in an informal conference with the OSHA area director, or to contest them before the independent Occupational Safety and Health Review Commission.

In FY 2003, the Labor Department's Occupational Safety and Health Administration conducted almost 40,000 inspections, and more than half focused on high-hazard industries.

OSHA Launches Hazard Communication Initiative

OSHA announced a new initiative to focus attention on hazard communication in the workplace, following an Agency review of current issues.  The HCS, adopted 20 years ago, covers some 650,000 hazardous chemical products and more than 30 million American workers.

"Appropriate and accurate hazard communication is essential to safe chemical management programs in the workplace," said Assistant Secretary Henshaw. "Employers need good information to design protective programs for their employees, and employees need the same information to protect themselves. This initiative will help improve that process."


  • Hazard Determination Guidance will help chemical manufacturers and importers identify the right information, assess it and translate it into a proper hazard determination. 
  • Model Training Program provides guidance for developing and conducting an employee training program, including a number of slides that employers can adapt to their workplaces. This is also posted for comment.
  • Guidance for Preparation of MSDSs will be posted for comment after comment periods close for the first two documents. It will address accuracy and comprehensibility of Material Safety Data Sheets (MSDSs) and will suggest sources of information and types of information to include. Chemical manufacturers and importers must develop MSDSs on each product they identify as hazardous.

Education and outreach are vital to compliance assistance efforts. OSHA has formed an Alliance with the Society for Chemical Hazard Communication (SCHC), a professional society that focuses on hazard communication issues. OSHA and SCHC will work together to produce several products for this initiative, including a course for small businesses on preparation of MSDSs; development of a training program for OSHA compliance staff on review of MSDS information; and development of a checklist to use to review MSDSs for the inclusion of certain information will be made available on OSHA's website. OSHA will also work with other Alliance Program participants to provide outreach on this issue.

They cover more than 1300 substances and are available in multiple languages.

For the enforcement component of this initiative, Compliance Safety and Health Officers will use sample hazard information on selected chemicals to check the accuracy of MSDSs. Deficiencies will be brought to the attention of the party responsible for supplying the MSDS, and failure to make corrections may result in the issuance of citations.

OSHA is also evaluating the adoption of the Globally Harmonized System of Classification and Labeling of Chemicals (GHS), and preparing a guide to increase awareness of the GHS. Adoption of the GHS in the United States could improve the quality of MSDSs and labels.