In this paper, we report the design of a simulated disaster management exercise that is used to explore the manner in which teams of emergency responders make sense of unfamiliar, dynamic situations. The paper develops a notion of sensemaking that combines semantic (i.e., extracting meaning from cues in the environment) and pragmatic (i.e., recognising opportunities for courses of action). This notion of sensemaking is explored in a study in which teams of experienced emergency responders, organised into different command structures, deal with the spread of a threat on a University campus. The results indicate how the command structures affect the ability of the teams to employ semantic or pragmatic sensemaking. Implications for supporting emergency response are considered.