This work presents a new topological methodology for critical measurements identification in observable networks. A measurement is said to be critical, in an observability sense, if its removal from the measurement set makes the associated system lose observability. The proposed methodology is based on the properties of both, observable measurement subnetworks (OMS) and redundant branch sets (RBS), for the first time proposed. To reduce the combinatorial bluster, the proposed method divides the measurements into two groups and classifies them into two phases. It allows identifying the critical measurements without any numerical calculation. Indeed, it is simple and fast. To clarify the proposed method and to demonstrate its simplicity, two examples are provided. The proposed method is successfully tested in the IEEE-14 bus system as well as in two realistic systems of Brazilian utilities. The first is a 121-bus system by ELETROSUL, and the other is a 383-bus system by Companhia Hidroele´trica do Sa˜o Francisco (CHESF).