The paper describes a lumped-parameter model for vented deflagrations of localised and layered fuel- air mixtures. Theoretical model background is described to allow insight into the model development with focus on lean mixtures and overpressures significantly below 0.1 MPa for protection of low- strength equipment and buildings. Phenomena leading to combustion augmentation was accounted based on conclusions of recent CFD studies. Technique to treat layered mixtures with concentration gradient is demonstrated. The model is validated against 25 vented deflagration experiments with lean non-uniform and layered hydrogen-air mixtures performed in Health and Safety Laboratory (UK) and Karlsruhe Institute of Technology (Germany).