This paper describes an approach to training emergency responders for mass casualty incidents. The approach is derived from a methodology and supporting software system called Summit. The Summit approach uses an integration of scenarios, hierarchical task analysis, interaction modeling, and expected utility theory to represent how actors engage in complex tasks; here we model mass casualty incident (MCI) activities supported by interactive technologies. Our goal is to ground MCI training in realistic scenarios and to demonstrate required response capabilities through associated hierarchical task analyses (HTA). The terminal nodes in an HTA are interactions, that provide a fine-grained model of the actors, technologies, data, and methods involved in realizing the required capability. The components of an interaction may have associated utility factors (benefits, costs, and risks) that provide learners with a rationale-based resource for understanding how different technologies are used to support MCI response efforts. Assessment of the approach is underway within a local EMS organization.