This work describes a large eddy simulation (LES) approach to model high pressure jet fires. Numerical simulations are compared against a large scale vertical, hydrogen jet fire test [Schefer, R. W., Houf, W. G., Williams, T. C., Bourne, B., & Colton, J. (2007). Characterization of high-pressure, under-expanded hydrogen-jet flames. International Journal of Hydrogen Energy, 32(12), 2081-2093], which gives experimental data for blowdown from a tank at an initial pressure of 413 bar through a 5.08 mm diameter nozzle. In this work, conditions 5 s after the start of the release have been taken to simulate a "quasi-steady" state. The work was driven by the need to develop contemporary tools for safety assessment of real scale under-expanded hydrogen jet fires and an aim was to study an LES model performance to reproduce such large scale jet fires in an industrial safety context. Detailed simulations of the flow structure in under-expanded part of the jet are avoided in this work using the notional nozzle concept. The LES combustion model is based on the mixture fraction approach and probability density function to account for flame-turbulence interaction. A flamelet library of the relationship between the instantaneous composition of the reacting mixture and the mixture fraction is calculated in advance. A comparison of experimental observations and simulation results (flame length, flame width) is discussed in view of the grid resolution required for LES and boundary conditions such as turbulence intensity and turbulent length scale at the notional nozzle. (C) 2009 Elsevier Ltd. All rights reserved.