The incident included both an airborne release of 55 gallons of blister agent, HD, over a populated harbor area in Connecticut, followed immediately by a truck explosion in the same area also releasing HD. The local responders identified HD during initial evaluation of the explosion site along with initial reports of symptoms. Later, continued reports of symptoms from persons not present near the explosion site, supported with intelligence information, led to discovery of the airborne release. Actual hot areas were not clear, and since HD is considered a relatively persistent chemical, concerns included contaminated people and vehicles that may have tracked contamination further from initial site.
Plume modeling was conducted via the IMAAC operational hub and area sampling showed some initial inconsistent results. However, significant environmental sampling was still necessary. Acute exposure action levels were evaluated to inform evacuation/shelter-in-place and responder PPE needs. Multiple agency experts, as part of the Technical Working Group, were convened under the auspices of the NRT and a discussion of sampling strategies and clearance decision criteria ensued. A consensus-based, interagency group was convened to determine a sampling strategy. A site-specific risk assessment was used to derive cleanup goals.
Each phase of the HD scenario exercise required site-specific decisions. During each phase, the possible exposure to the general public and response workers was monitored using field screening and expedited on-site and off-site laboratory analysis. Exposure guidelines for the general public can be found in Appendix A.