Apart from technical reliability, usability is one of the major criteria for safe and efficient usage of interactive information technology in disaster and emergency management. However, in this setting, usability evaluation is difficult due to the heterogeneity and unpredictability of operation conditions, as well as the difficult, usually mobile, context. However, there are ways to conduct usability evaluations in disaster and emergency settings. Thus, in this paper, advantages and disadvantages of empirical and analytical usability evaluation methods for interactive systems in disaster and emergency management are discussed. The importance of formative evaluation measures within an iterative human-centered design process is emphasized. It is illustrated by two case studies dealing with paramedics' and emergency physicians' usage of mobile and wearable devices in mass casualty incidents.