The invention relates to a procedure for determining the risk of flammability of a mixture of two reactive gases A, B, in an inert or base gas, characterized in that it comprises: a step of determining, in the flammability diagram for the A/B/base gas mixture, the change in the composition of the mixture in order to determine whether or not the composition has passed through the flammability region of the said flammability diagram, when A is firstly injected into the inert or base gas in order to form a first mixture and then B is injected into the first mixture in order to form the final mixture; a step of comparing the mixing time, should the region have been passed through, with the chemical induction time for the mixture.