The pressure peaking phenomenon can be observed when hydrogen is released in enclosures with vent(s). The unforeseen physical phenomena of pressure peaking has been described and explained. This phenomenon occurs for hydrogen releases in enclosures where the vent(s), volume, and leak rate are such that there will be no air ingress to the enclosure. Pressure peaking describes the physical phenomenon of a peak in the pressure transient during such a release for some release conditions in a vented enclosure. This phenomenon is pronounced only for gases lighter than air, e.g. hydrogen and helium. For particular release flow rates and vent sizes the peak can be an order of magnitude higher compared to the steady-state overpressure that is reached when the enclosure is fully filled with hydrogen over time. This finding is relevant to all hydrogen applications indoors from a fuel cell in an enclosure or laboratory scale storage up to a forklift in a warehouse. The peak magnitude depends on the release flow rate, hydrogen inventory, enclosure volume and the ventilation area, and potentially can exceed the maximum pressure which the enclosure can withstand. A look up nomogram for applicability of the developed theory that is based on vent area and leak rate has been created for sustained releases. Experimental evidence of the phenomena is described. Reduced analytical equations are presented for the case of a constant flow rate release, and the associated nomogram is presented for use by hydrogen safety engineers and regulators. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.