Broadcasting emergency messages has been widely recognized as an important area of research. A crucial issue, in this context, is to ensure the correctness of broadcasting protocols using a formal method to prevent errors before their implementation. In this paper, we propose a new protocol for broadcasting emergency messages in order to inform persons in case of an unexpected situation occurrence. Our protocol consists in applying a clustering mechanism before proceeding with the broadcasting phase. This mechanism is one of the most efficient techniques used in a large-scale network. We formally verify the proposed protocol using the Event-B formal method which supports an incremental development based on the refinement technique.