Sandra Nilsen et. al Determination of Hazardous Zones Case study: Generic Hydrogen Refuelling Station

Date: Page: 2 Background Aim of zone classification Central requirements outlined in /92/EC Safety and health protection of workers potentially at risk from explosive atmospheres - IEC/EN …Part 10 Classification of hazardous areas IEC standard opens for ventilation to avoid zone classification when volume of explosive atmosphere is negligible Conclusions from HySafe work – Italian Guidelines recommended Kommentarer: legg inn et bilde her

Date: Page: 3 Definitions Hazardous area Area in which an explosive gas atmosphere is present, or may be expected to be present in quantities such as to require special precautions for the construction, installation or use of apparatus Zone 0 An area in which an explosive gas atmosphere is present continuously or for long periods Zone 1 An area in which an explosive gas atmosphere is likely to occur in normal operation. Zone 2 An area in which an explosive gas atmosphere is not likely to occur in normal operation and, if it does occur, is likely to do so only infrequently and will exist for a short period only

Date: Page: 4 Italian Guide 31 – 35 and Guide 31-35/A Stepwise process, giving guidelines on - Leak size dependent on component - Flow rates for continuous releases as a function of component - Reference formulas for calculation of flow/leak rates - Evaluation of the extent of the hazardous zone as a function of release flow rate, ventilation and flammable substance Gas dispersion calculations to determine the extent of the hazardous zones

Date: Page: 5 Italian Guidelines - Risk Based Approach ZoneLikelihood of presence of explosive atmosphere in 1 yr Total duration of release in 1 yr Zone 0 P > More than 1000 hours Zone  P > More than 10 hours up to 1000 hours Zone  P > More than 0.1 hours up to 10 hours

Date: Page: 6 Generic Hydrogen Refuelling Station Assumptions Delivery 60 Nm3/h Pressure:15/460 bar 3 pressure banks - 8 storage vessels Max storage volume 200 kg Gas in process eqipment in building: 300 g Valve/piping dimensions: 5 – 15 mm Simplified process drawing Horisontal view

Date: Page: 7 Scenarios considered for zone classification Valve leak inside dispenser enclosure Opening of safety valve - vent line for the safety valves Outdoor valves at storage vessels Refuelling nozzle Valve at buffer tank Shutoff valve outside gas processing building Releases inside the gas processing building

Date: Page: 8 Relevant leak frequency and leak size Relevant leak frequencies for this type of technology/installation not available Considered 3 different leaks sizes (release diameter) for valves - 0,56 mm (from Italian met.) -> release rate 5.7 g/s - 0,2 mm -> release rate 0.7 g/s - 0,1 mm -> release rate 0.2 g/s

Date: Page: 9 Gas processing building Ventilation capacity: Natural: 0.5 m/s Mechanical: 10, 150, 300, 800 ACH Inside gas processing building Ventilation Design 1 Ventilation Design 2: Fan location in the middle of the roof, 2 louvers at lower part of long walls 6 x 0.5 m

Date: Page: 10 Results – Gas Processing Building Results for ventilation Design 2 Based on LFL assumed as basis for the determination of the zones

Date: Page: 11 Gas processing building Importance of risk reducing measures ESD activated by gas detection Reliable non-return valves downstream compressor - outdoors …if not leak from the non-return valve itself will be the representative leak scenario - backflow from 460 bar

Date: Page: 12 Outdoor valve at storage vessels Significant difference in zones dependent on LFL or ½ LFL Experimental data indicate that ignition might be difficult between 4 and 8 vol%

Date: Page: 13 Summary Italian method recommended - Systematic analytical method, verification of zones based on a risk based approach Hazardous zones at generic hydrogen station based on 0.56 mm leak diameter: - Zone 2 inside gas processing building - More than 300 ACH and prevention of back flow -> no hazardous area - Zone 2 radius 5 or 3.5 m around outdoor HP valves

Date: Page: 14 Needs for improvement Obtaining relevant leak frequency and leak sizes coupled to new technology and new user groups Experimental studies on ignition probability in realistic release conditions Verification of CFD tools tools for prediction of gas dispersion in confined and obstructed areas

Date: Page: 15 hydro.com