CSB Issues Urgent Recommendations

Yesterday I addressed the CSB vs SSI issue reported in yesterday’s press conference and press release about the Chemical Safety Board’s investigation of the CITGO explosion and fire on July 19th at their Corpus Christi refinery. There was another, equally important issue raised in that press conference (more immediately important to people living and working around the CITGO refineries mentioned), the apparent inadequacy of the hazard mitigation procedures to protect people from catastrophic releases of hydrogen fluoride gas from storage. According to the press release:

“The refinery used a water spray system to absorb the released HF, but the CSB cited scientific literature to conclude that at least 4,000 pounds of HF likely escaped from the unit into the atmosphere and left the facility. Investigators determined that during the first day of response efforts CITGO nearly exhausted the stored water supply for the water mitigation system. Approximately eleven-and-a-half hours after the initial release, before the water supply was completely exhausted, the refinery began pumping salt water from the ship channel into the refinery fire water supply. Multiple failures occurred during the salt water transfer including ruptures of the barge-to-shore transfer hoses and water pump engine failures.”

While the investigation has yet to be completed, the CSB took the unusual step of issuing and “urgent safety recommendations calling on CITGO to immediately improve its emergency water mitigation system in the event of another release of potentially deadly hydrogen fluoride (HF) vapor”. They also recommended an independent safety audit be conducted of the hydrogen fluoride units at all of their refineries. The Board only issues such early recommendations when they “determine an imminent hazard may be present and has the potential to cause serious harm unless rectified in a short timeframe”. Water Spray Mitigation Systems A number of high risk chemical facilities across the country with toxic release COI use similar type water spray systems for release mitigation. Such water sprays convert a toxic gas cloud to a toxic gas dissolved in water that presents a much smaller risk to the neighboring or downwind community. The effectiveness of such systems depend on a number of complex issues including (but certainly not limited to), rate of gas release, amount of gas released, wind speed, wind direction, water flow rates, water spray dispersion patterns and the amount of available water. Since many of these factors cannot be determined in advance the design process for these systems requires the engineering staff to make a number of assumptions about the release incident that might occur. Safety system designers will make these assumptions based on a wide variety of factors including probable failure modes based on past histories. If a new failure mode is ‘discovered’ during a process incident it is likely (as in this case) that the design basis will be inadequate for that new scenario. What CSB is essentially saying in this instance is that the CITGO process engineers did not take this type release scenario into account when this water mitigation system was designed. With the actual data now available for this release case, those engineers need to go back and redesign the system. Other facilities with similar systems will need to model their systems against the CITGO release data to see if their design would be adequate to mitigate a similar type release at their facility. Counter Terror Water Spray Mitigation I have long advocated that this type of water spray system should be included in the Site Security Plan for facilities with toxic release COI. The idea being that in the event of a terrorist attack, this type system would be in place to backstop a failure in security measures that could allow for a successful terrorist attack. Again, it would be just another layer in the site defenses. The apparent failure of the safety mitigation system at Corpus Christi emphasizes how difficult it is to adequately design such a system; even when there is a process history to provide input into the design model. Since not terrorist attacks have been conducted against such facilities, there is no current history to draw from for modeling a system for mitigating a terrorist attack. This means that even more assumptions must be made about the variables that affect the efficacy of such a system. Perhaps it is time for the Federal Government and industry to fund some studies of potential storage tank failure modes from terrorist attacks so that spray mitigation designers have more data upon which to base their designs.