The diploma thesis is focused on a detection and a laboratory control of hazardous substances’ leak into the environment. These hazardous substances are classified. Further, it aims to chemical laboratories of the fire-brigade of the Czech Republic, as well as which place they hold in the fire-brigade system, and it indicates their main duties. This diploma thesis contains a review of some essential types of devices and mediums, which are in terms of the fire-brigade of the Czech Republic usable to practice the detection, determination and assessment of the hazardous substances in various figures of the environment in terrain, i.e. filling of duties of the chemical survey. The output of this diploma thesis is simulation of leaks of the toluene diisocyanate using ALOHA software, TerEx software and Rozex Alarm software. Further on, the proposal of another methodical sheet focused on leak actions of the concrete hazardous industrial substance – toluene diisocyanate. This methodical sheet could therefore broaden pro tempore elaborated sheets for chlorine and ammonia.