In building fire evacuation, good guidance can speed up egress process and occupants may be injured due to lack of information and guidance. There are many studies on building egress systems, which use relevant information (e.g., fire condition and its evolution) to calculate and provide guidance to occupants. However, information used to generate guidance may be uncertain, and it is difficult to provide the guidance under uncertainty. How to provide effective guidance to occupants under uncertainty and how to evaluate the confidence of the guidance are critical issues. To describe the confidence of the guidance, the concept of “confidence intervals” is used. By comparing “confidence intervals” with a threshold, acceptable guidance is provided. Testing examples show that the confidence of the guidance can be evaluated and unacceptable guidance can be differentiated with the use of confidence intervals.