The paper presents a review of state of the art in modelling of accidental gaseous deflagrations. A critical analysis of main approaches to model gaseous deflagrations, i.e. lumped parameters models and CFD simulations, is performed briefly. The correlation for quantitative estimation of venting generated turbulence in enclosures without substantial congestion is given. An advanced vent sizing technology is discussed whose predictions are, in about 90% of considered cases, closer to experimental data than the vent sizing technique of the NFPA 68 standard. It is demonstrated that new vent sizing technology has fewer limitations and the same formulas are valid for elevated initial pressures and temperatures. It is demonstrated that elevated initial temperatures could lead to both increase and decrease of reduced pressure depending on explosion conditions. A procedure is outlined that determines the maximum external overpressure as a function of the distance from the vent. The equation for scaling of upper limit of inertia for vent covers of 100% "efficiency" is given. Similarity number for scaling vent cover inertia with turbulence is derived. A new original technique of vent sizing for equipment and buildings with "unknown performance" mixture is presented for the first time.