By Holly Maher
On July 28, 2014, one contract worker was killed and another seriously injured when an explosion occurred within a fish oil storage tank, blowing the lid off the 30 foot high vessel. Contractors were on top of the tank, performing required welding on the tank. The storage tank contained approximately 8 inches of “stickwater” or a slurry of water and fish matter thought to be non-hazardous.
Although the official investigation of this incident continues with participation from both OSHA (Occupational Safety and Health Administration) and the CSB (Chemical Safety Board), we can use a Cause Map to visually lay out the cause and effect relationships known at this point. As information becomes available, additional causes can easily be added to the Cause Map.
The first step in the Cause Mapping process is to identify the problem by filling out the Outline. We clarify the date, time, location, and sometimes “what was different about this incident”, which at this point is unknown. The explosion occurred at ~9:30 on the morning of July 28th, 2014 at a fish processing plant in Moss Point, Mississippi. The task being performed when the incident happened was welding on the storage tank. At the bottom of the outline we identify the impact to the goals for the organization, because although you may get many answers to “what is the problem”, the impact to the goals will provide a common starting point for the investigation. In this case, the primary goal impacted was the fatality and serious injury related to the explosion. The tank damage and downtime in the facility could also be captured, however we have focused our discussion here on the safety goal impact.
Once we have identified the goals impacted, we can start the analysis by simply asking some “why” questions. Why was there one contractor fatality and one serious injury? Because there was an explosion. Why was there an explosion? Because there was an ignition source. Why was there an ignition source? Because contractors were welding on the tank. “Why” is a great way to get any investigation started, but we also want to expand the analysis to ensure all the causes are identified (the system of causes, if you will). In this case, the explosion is caused not just by the ignition source, but also the presence of fuel and the presence of oxygen (think fire triangle).
The ignition source was caused by the welding on the tank, which was being done for repairs and because the workers were unaware of the combustible atmosphere in the tank. The workers were unaware of the combustible atmosphere because there was no atmospheric testing done on the vapor space in the tank because the stickwater was considered to be non-hazardous. Unlike the oil and gas industry, where the potential for flammable or combustible atmospheres is well known and managed through atmospheric testing, the potential is less well known in industries, such as fish processing, where organic microbiological fluids can release flammable gases, creating a potential risk when doing maintenance work that is spark or heat producing (hot work). The fuel source for the explosion was methane and hydrogen sulfide being released from the stickwater. A sample of the material was sent to the lab after the explosion and the presence of these off-gases was identified. The flammable gases were present because there was 8 inches of stickwater present in the tank.
The Cause Mapping process allows us to identify all the causes related to an incident with the goal of identifying the best solutions to mitigate potential future risk. Even with this initial analysis, we can start to identify potential solutions to mitigate the risk of this incident occurring again. Clearly, the potential hazards from flammable atmosphere is not well known in industries with mixtures of water and organic material (e.g. fish processing, pulp processing, potato processing), so lessons learned from this incident, along with others investigated by the CSB, would be worth sharing across the industry. In addition, requiring atmospheric testing for hot work would mitigate the potential for explosions during these types of maintenance activities. Another option would be to drain and clean the tank prior to welding activities. These solution could have significant, global impact across all types of hot work activities.