This paper presents data on the limiting (minimum) concentrations of hydrogen in oxygen, in the presence of added helium, at-elevated temperature and pressure related to the practical operational case. A 5 L explosion vessel, an ignition sub-system and a transient pressure measurement sub-system were used. Through a series of experiments carried out using this system, the limiting concentrations of hydrogen in oxygen and helium at different initial pressures and temperatures for the practical operational case were studied, and the influence of ignition energy and initial temperature on the limiting concentration of hydrogen in oxygen and helium was analyzed and discussed. The variation of ignition energy within the studied range is found to have a significant effect on the limiting concentration of hydrogen in oxygen and helium at lower initial temperature. However, when the ignition energy is higher than 32 mJ, the limiting hydrogen concentration remains almost changeless as the initial temperature increases from 21 degrees C to 90 degrees C. The limiting explosible concentration of hydrogen oxygen helium mixture decreases as the ignition energy increases when the initial temperature is lower. When the initial temperature is higher, the ignition energy has little effect on the limiting hydrogen concentration of hydrogen oxygen helium mixtures. When the initial temperature reaches 90 degrees C, the limiting hydrogen concentration remains almost changeless with an increase in ignition energy. The limiting explosible concentration of hydrogen in the mixtures, at the initial temperature of 21 degrees C and the ignition energy of 0.5 mJ, is 8.5% and that of oxygen is 11.25%. (c) 2014 Elsevier Ltd. All rights reserved.