One concentration was the "toxic endpoint," defined as the maximum concentration below which most individuals could be exposed for up to an hour without experiencing irreversible or other serious health effects. The other was the "immediately dangerous to life or health," or IDLH, the concentration that poses an immediate danger to life, would cause irreversible health effects, or would impair an individual's ability to escape danger.
For the larger release, the toxic endpoint would be 3.9 miles from the plant, stretching into St. Albans, Dunbar, South Charleston and Nitro. The IDLH would be 1.2 miles from the plant.
For the smaller release, the toxic endpoint would be 2.8 miles from the plant and the IDLH would be 1.1 miles from the facility.
The study is similar and uses similar computer modeling to the "worst-case scenario" reports that Kanawha Valley companies made public in 1994 in anticipation of a federal requirement that they file such reports with the U.S. Environmental Protection Agency.
In their lawsuit over the MIC unit, 16 Kanawha Valley residents cited a "worst-case" report Bayer submitted to EPA, warning that 300,000 people within a 25-mile radius could have been affected by the plant's former inventory of more than 200,000 pounds of the chemical.
Bayer lawyers respond that such an incident is "both a physical and practical impossibility" because the worst-case report assumes "that none of the multiple layers of protection that [Bayer] employs to prevent precisely such an event were in place, or would function."
The scenarios in the CSB report were specifically aimed at providing some rough glimpse of how far impacts might have been felt if the MIC "day tank" had released some of its 13,700-pound contents the night of the explosion and fire.
In its final report last month, the board said that the steel "blast shield" around the day tank likely would have protected the tank itself, but that piping attached to the tank could have been damaged by debris.
John Vorderbrueggen, the board's investigations supervisor, cautioned that the study design could overstate the extent of the releases.
For example, both scenarios involved MIC piping being essentially cut in half, rather than punctured by a smaller hole. Also, the study assumed that most plant safety equipment that could control the size of a release is not working at the time of the incident.
But, the study also does not consider whether weather conditions could have blow the plume in the direction of a residential neighborhood and then kept it hugging against the valley floor and hillside, increasing exposure time. The report also does not attempt to quantify the risks of such leaks occurring or analyze in any way what the actual health impacts on residents might be if they occurred.
TAI Engineers' report to the CSB is dated April 20, 2009, or one day before a high-profile congressional hearing that examined the Institute explosion and Bayer's efforts to use homeland security rules to avoid embarrassing disclosures about the facility. Two days after the congressional hearing, on April 23, 2009, the board held its own public hearing in Institute to release preliminary findings of its investigation.
Board officials did not reveal the leak modeling report's findings at either hearing, and Vorderbrueggen told residents at the Institute hearing, "We do intend to run some air modeling to predict what kind of chemical release might occur in the impact zone."
In an interview Thursday, Vorderbrueggen said he did not remember exactly when the board received the report from TAI Engineers.
"Just because the report has that hard fast date doesn't mean it was in our office that day," Vorderbrueggen said. "What transpired exactly over the three, four, five, six days related to this April 20 date on the coverage page of this report, I'm not even sure it could be reproduced."
Board officials had originally said they would include the modeling results in their final report, but Vorderbrueggen said investigators decided not to do so when Bayer announced in August 2009 that it was eliminating the MIC day tank.
Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.