On the implementation of an International Curriculum on Hydrogen Safety Engineering into higher education

This paper describes the implementation of an International Curriculum on Hydrogen Safety Engineering into higher education. The curriculum is being developed as part of the educational and training activities of the European Network of Excellence Safety of Hydrogen as an Energy Carrier (HySafe) and has been implemented into a 1-year Postgraduate Certificate Course in Hydrogen Safety Engineering by the University of Ulster. The course is taught in the distance learning mode and comprises of two 30 CATS-point modules, namely, ‘Principles of Hydrogen Safety’ and ‘Applied Hydrogen Safety’. The first delivery of this course began in January 2007 and the second delivery will commence in September 2007.     

Unified correlations for vent sizing of enclosures at atmospheric and elevated pressures

Innovative vent sizing technology is presented for explosion safety design of equipment at atmospheric and elevated initial pressures. Unified correlations for vent sizing are suggested. They are modifications of previously reported correlations verified thoroughly for experimental data on vented gaseous deflagrations under different conditions but only at initial atmospheric pressure. Suggested correlations are based on experimental data on vented deflagrations of quiescent and turbulent propane–air mixtures at initial pressures up to 0.7 MPa. Typical values of turbulence factor and deflagration–outflow interaction number are obtained for experimental vented deflagrations at initial pressures higher than atmospheric.

“Blind” examination of new vent sizing technology on another set of experiments with methane–air and propane–air mixtures has shown that predictions by suggested vent sizing technology are better than by the NFPA 68 guide for “Venting of Deflagrations”.

In the development of recently reported results for initial atmospheric pressure it has been concluded that the innovative vent sizing technology is more reliable compared to the NFPA 68 guide at elevated initial pressures as well. Moreover it is crucial that the calculation procedure remains the same for arbitrary deflagration conditions.     

Towards hydrogen safety engineering for reacting and non-reacting hydrogen releases

Hydrogen Safety Engineering (HSE) is the application of scientific and engineering principles to the protection of life, property and environment from adverse effects of incidents/accidents involving hydrogen. Validated engineering tools for calculation of flammable envelope size and hydrogen jet flame length are of importance for calculation of safety distances. This paper compares the University of Ulster (UU) methodology for calculation of safety distances based on the similarity law for concentration decay in non-reacting jet, and the approach given in the standard NFPA 55 (NFPA 55, 2010). It is shown that NFPA 55 can overestimate an axial distance to the lower flammability limit up to 160%. Two correlations for hydrogen jet flame length are compared. One approach (Sandia National Laboratories) correlates the dimensionless flame length with the flame Froude number, and another (UU) associates the flame length with a new similarity group, which is a product of mass flow rate and nozzle diameter. Both approaches are compared against 123 experimental data on expanded and underexpanded jet flames. In the typical for hydrogen applications momentum-controlled regime the first approach has scattering of experimental data 50% while the second approach gives only 20% and thus is preferable for the use by hydrogen safety engineers.     

Numerical analysis of hydrogen deflagration mitigation by venting through a duct

This paper presents a model and simulation results for the mitigation of a hydrogen–air deflagration by venting through a duct. A large eddy simulation (LES) model, applied previously to study both closed-vessel, and open atmosphere hydrogen–air deflagrations, was developed further to model a hydrogen–air explosion vented through a duct. Sub-grid scale (SGS) flame wrinkling factors were introduced to model major phenomena which contribute to the increase of flame surface area in vented deflagrations. Simulations were conducted to validate the model against 20% hydrogen–air mixture deflagrations (vent diameters 25 and 45 cm) and 10% hydrogen–air mixture deflagration (vent diameter 25 cm). There was reasonable correlation between the simulations and the experimental data. The comparative importance of different physical phenomena contributing to the flame wrinkling is discussed.