The possibility of risk assessment for operating hazardous production facilities, including explosion hazardous zones, is considered.

The current standards are analyzed, in which the definition of «risk» is given, and, also the components clarifying it and the conditions for their use. The definition of risk given in GOST R 57149—2016 is considered as the most acceptable for assessment of the operating conditions of hazardous production facilities. According to this GOST the risk is defined as a combination of the probability of causing damage and the severity of this damage.

The advantage of this approach is the possibility of calculating quantitative indices. General risk calculation formula is given.

The known methods for risk calculations approved by the orders of Rostechnadzor were analyzed, and it is shown that the risks described in them relate to particular cases. This confirmed the need in developing the detailed formula for calculating the probability of the explosion-proof operation of hazardous production facilities.

To solve the main problem, the concept of «explosion hazard» is formulated: this is the probability of an explosion occurrence in explosion hazardous zone due to the probability of explosive environment when there is a probability of initiating physical effect.

The basis for the wording of the probabilities lies in the set of IEC 60079 codes: for the probability of presence of explosive environment — in the classification of explosion hazardous areas (0, 1, 2, 20, 21, 22), for the probability of initiating effects — in the form of the list of initiating physical effects.

The formulas derivation for the above probabilities is made based on the theory of probability. Considering the obtained formulas, the generalized formula for risk calculation was recorded.