Improving the safety of human life is one of the main tasks of scientific and technological progress. A dangerous situation occurs when a person is in a dangerous area, i.e. in a space where constantly, periodically, or occasionally there are situations caused by factors that lead to gradual or instantaneous damage to human health. Fire is one of these situations. The safety of technical systems is solidly linked to their reliability. In firefighting automation, the main purpose of calculating reliability is to determine the probability of failure-free operation of the equipment of the system. The value obtained is subsequently used to calculate individual fire risk. To ensure technical safety, it is a universal practice to use system approach and system analysis, which allows us to consider technical security as a system. One of the specific characters of determining the reliability of computer-aided systems is the difference between the reliability indicators of the main elements of the system and the automation system as a whole. The more complex the system, the less reliable it is. The article considers the main problems leading to the efficiency loss of particular items of equipment included in the technical safety systems and formulates the tasks and methods for their reliability assessment. The research features the fire safety system of an industrial building, which includes an automatic fire alarm system and a warning and evacuation system. The paper contains an example of calculating the reliability for an automatic fire alarm system. The authors propose some ways of improving the existing system. The results are processed and presented by the main indicators of system reliability, which are the failure rate and the failure-free operation probability for particular items of equipment and the system as a whole. The research revealed that a manual detector, used as a standby item in the system of thermal and smoke fire detectors, makes it possible to reduce the failure rate of the system and increase the average time of failure-free operation. Thus, it improves the indicators of the system reliability and increases the safety of industrial buildings.