According to the normative documents and normative legal acts on fire safety existing in Russian Federations, each building or a construction has to have the space-planning solution and design of evacuation ways providing safe evacuation of people at the fire. Safe evacuation of people from buildings and constructions at the fire is considered provided if time interval from the moment of detection of the fire before completion of process of evacuation of people in a safe zone doesn’t exceed necessary time of evacuation of people at the fire. People begin to be evacuated from the building at the fire later some period which is called time of the beginning of evacuation. This size represents set of “technical” and “psychophysical” components. One of “technical” parts is fire detection time. Conclusion about safe evacuation of people from the building or the value of probability of evacuation of people is defined proceeding from calculation methods in which time of detection of the fire isn’t considered in an explicit form. The purpose of the offered work is fire detection time assessment as period from the beginning of the fire before his detection by means of fire alarm equipment (before achievement of threshold values for fire detectors), on the basis of the modern program complexes used for modeling of dynamics of the fire. It is established that the growth rate of development of the fire is the defining factor influencing both for the period of fire detection and for necessary time of evacuation in general. Not accounting of time of detection of the fire as derivative of growth rate of development of the fire, on the basis of calculation methods, can lead as to increase in necessary time of evacuation, and reduction of time of the beginning of evacuation that in turn involves unauthenticity of the received results.