This paper demonstrates experimental and numerical study on spontaneous ignition of H-2-N-2 mixtures during high-pressure release into air through the tubes of various diameters and lengths. The mixtures included 5% and 10% (vol.) N-2 addition to hydrogen being at initial pressure in range of 4.3-15.9 MPa. As a point of reference pure hydrogen release experiments were performed with use of the same experimental stand, experimental procedure and extension tubes. The results showed that N-2 addition may increase the initial pressure necessary to self-ignite the mixture as much as 2.12 or 2.85 - times for 5% and 10% N-2 addition, respectively. Additionally, simulations were performed with use of Cantera code (0-D) based on the ideal shock tube assumption and with the modified KIVA3V code (2-D) to establish the main factors responsible for ignition and sustained combustion during the release. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.