A major safety problem at present is the lack of an agreed methodology to estimate blast loads from hydrogen (H2) vents. Of particular interest is the delayed ignition of the flammable clouds that form upon a controlled or uncontrolled release. This study aims to test and improve an existing methodology to enable more accurate prediction of overpressure in hydrogen venting scenarios. Present deflagration model underestimates overpressures by an order of magnitude, whereas the detonation model results in overly conservative estimates albeit useful to retain as an upper limit. While in safety assessments, a certain degree of conservatism is preferred due to the non-negligible potential consequences, estimates should be realistic and in line with the physics that expected to play a role emphasising the need to improve deflagration modelling.