On September 18, 1998, at about 10:38 AM local time, at the Monsanto Company Plant in Luling, Louisiana, a pipe nipple fractured allowing a release of ammonia gas into the atmosphere. The release of 1,010 kilograms (2,227 pounds) of ammonia (NH3) lasted for two hours, with most of the material (936 kilograms = 2,064 pounds) released during the first hour. The release consisted of a high velocity horizontal jet which generated an initial cloud expanding into a volume source. After the initial jet expansion, the plume traveled downwind carried by the wind and expanding according to the laws of atmospheric transport and diffusion.
We were retained by the attorneys representing Monsanto and asked to review the case and simulate the concentration and odor impact of the NH3 cloud. We selected the Industrial Source Complex (ISC3) model for this simulation. We calculated the characteristics of the emission scenario and collected local meteorological data. Our concentration results are shown in Figure 1. We were able to determine that the lowest ERPG value, the ERPG-1 value of 25 ppm for NH3, only exceeded in a small region close to the source. In the community, outside the Monsanto's fenceline, NH3 concentrations are 100 times (or more) lower than the lowest ERPG value.
To better visualize the actual dynamics of the event, we also used a dynamic, Lagrangian particle model to simulate the release and produced an animation (Video 1) of the results.
|Figure 1 ||Video 1 (low resolution)|