This paper treats the real-time sensing-based risk-mitigation control of hydrogen dispersion and accumulation in a partially open space with low-height openings by forced ventilation. A hunting-preventive control scheme that we previously proposed (Matsuura et al., Int J Hydrogen Energy, 2012;37(2):1972-84) has parameters such as the monitoring period of hydrogen sensors T-p, a unit increment in the exhaust flow rate per area from a roof vent alpha, and a threshold epsilon for the change in the exhaust flow rate. Through parametric simulations of the hydrogen exhaust after leakage ceases, we clarify the effects of the parameters on the rate of exhaust flow from the roof vent and the amount of hydrogen accumulating near the roof, which are critical for ventilation performance. With a selected combination of (T-p, alpha, epsilon) for which the ventilation system has a quick response and reasonable original performance, we first introduce two acceleration methods separately to the original hunting-preventive scheme to improve the ventilation performance after hydrogen leakage ceases. Ventilation performance employing the two methods is compared with that employing the original scheme. From the results, a hybrid method is finally proposed. The effectiveness of the proposed method is computationally validated for leak flow rates of 9.44 x 10(-4), 4.72 x 10(-4) and 2.36 x 10(-4) m(3)/s. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.