Since its discovery in 1864 by Cailletet [1], hydrogen embrittlement of metals has been the target of several investigations. In 1962 Devanathan and Stachurski [2], developed an electrochemical technique for hydrogen permeation. There are now three methods to produce hydrogen: galvanostatic, potentiostatic and under open circuit potential in an acid medium (OCPAc). Regulations in Refs. [3] and [4] standardized hydrogen permeation only by the potentiostatic method. In the present work an experimental methodology for OCPAc procedure was developed. The authors conclude that the equation of diffusivity proposed by ISO 17081 and ASTM 0148-97 [3] and [4] can lead to underestimated diffusivity values. The authors conclude the mathematical model proposed for the OCPAc method presented a satisfactory fit to the experimental data. Diffusivity values were calculated not only for this case but also for all other methods. However, to evaluate and explore the limits of the proposed methodology, the authors recommend its use with other metals and alloys. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.