The paper deals with industrial chemical safety with a focus on major chemical accidents, hazardous chemicals and mixtures with emphasis on the dangers of selected sub-limit sources of risk. Currently, the two main laws in force, the Major Accident Prevention Act of 2015 (1), or the so-called "Chemicals Act" or the Chemicals and Mixtures Act of 2011 (2), have failed to address the serious safety issues of the so-called "Sub-threshold sources of risk" consisting of the low masses of hazardous chemicals.
Until 2017, there was no clearly defined professional methodology, procedure or other tool to assess risk assessment of sources with hazardous chemicals and mixtures.
The main part briefly mentions the instruction of the General Director of the Fire and Rescue Service of the Czech Republic (Instruction 35/2017 (3)), which solves the issue very well and provides professional and methodological instructions for capturing and evaluating sub-limit sources of risk. This clearly improves the prevention of these events, it also increases the preparedness for possible emergency releases of hazardous substances and, last but not least, it can also increase the preparedness of the population for the correct response to releases of below-limit amounts of certain hazardous substances.

Keywords: hazardous chemical substances; prevention of major accidents; sub-limit sources of risk; accidental releases of hazardous substances; modelling of accident impacts