Pervasive computing allows data to be collected using sensors and mobile devices. Recent studies, however, show that in emergency and crisis situations conventional access control mechanisms are too rigid for information sharing. There is an increasing need to secure the information collected from the pervasive computing environments, and yet to be able to allow flexible data sharing to facilitate problem-solving and decisionmaking. Our work investigates the two seemingly contradictory factors, secure access and flexible adaptation, and designs a trust inference model for emergency and crisis situations. We describe an ad hoc trust inference model where access decisions are adaptive to the identity, history, and environment of a requester, for example, the degree of urgency. Our trust inference model is built on fuzzy logic. Our sharing control mechanism can also be applied to protect personal data and used for digital identity protection.