||Resulting from an interdisciplinary endeavor, the paper proposes an ontological model for supporting collaborative work practices in critical settings, and shows its application to a specific domain. The model is empirically-grounded, as based on ethnographic research carried out at an international airport ?clearly an example of safety-critical environment, where emergency prevention and preparedness are crucial. On the other hand, the model leverages on previous ontological work on collaboration and observation in emergency response, and revises it when necessary, thus contributing to its development. Taking hand-baggage screening as an example, the paper shows how the model can be applied, and how it could be used to run model-based simulation in order to better understand collaborative work practices and analyze the impact of different techno-organizational changes on such practices and their effectiveness. This could result in suggesting guidelines for enhancing workflow, security policies and, more generally, time- and safety-critical situations management.