Defining Hazardous Zones – Electrical Classification Distances Gary Howard,Andrei Tchouvelev, Vlad Agranat and Zhong Cheng Defining Hazardous Zones – Electrical Classification Distances Gary Howard, Andrei Tchouvelev, Vlad Agranat and Zhong Cheng

Acknowledgements Work partially supported by –Natural Resources Canada (NRCan) CTFCA Clearance Distance Project –Natural Sciences and Engineering Research Council of Canada (NSERC) Industrial Research Fellowship

Project Objectives To develop sound scientific and engineering guidelines that can be used to specify quantitative values for: –Clearance distances for hydrogen equipment and systems –Hazardous zone classifications –Declassifying hazardous zones with ventilation To interpret the new specifications and to develop scientifically based "rules of thumb" that can be used as input into the Canadian Hydrogen Installation Code and for updates to the Canadian Electrical Code

Approach CFD modeling and thermal effects analysis of typical releases under: Real operating conditions Real geometries Real ventilation rates (indoor) and wind velocities (outdoors) Release Direction Release Magnitude Large/fastSmall/slow Vertical Horizontal

Simulation Examples

Key Results – Innovative Approach Proposed clearance distances are based on CFD modeling results that were obtained based on hydrogen properties and science Proposed clearance distances depend on both storage pressure and storage volume: –Three pressure ranges were selected: up to 25 bars, up to 440 bars and above 440 bars to differentiate between on-site hydrogen generation equipment, and 350 and 700 bars ground storage, compression and dispensing equipment –Several volume ranges were selected to differentiate between on-site hydrogen generators inventory, small lab type or demo type storage and medium to large scale storage systems Proposed clearance distances are based on LFL concentration envelopes plus safety factor of 25%

Example of Scenarios and Assumptions H2 leak rates of 5 and 20 scfm ( and kg/sec) were selected as credible leaks based on experience; the necessary holes sizes to produce this leak rate were calculated for 400 bar storage pressure (0.1 and 0.2 mm respectively) Selected leak rates were modeled in downward, upward and horizontal orientations in a 0.5 m/sec wind (IEC ) Flowrate (SCFM) Re # % vol. H 2 cloud volume (m 3 ) Horizontal cloud extension (m)Vertical cloud extension (m) IECCFD8 % vol.4% vol.2% vol.8 % vol.4% vol.2% vol. 20 (down) *3.31*0.63* 5 (down) * * 20 (up) (up) (horiz.) (horiz.) * These clouds touch the ground, which is 3 m below the leak orifice

5 and 20 scfm Simulation Results at 400 bars 5 100% 50% LFL % 50% LFL 5 100% 50% LFL % 50% LFL 5 100% 50% LFL % 50% LFL CFD LFL Vol m3

Key Differences with IEC IEC method of hazardous location size calculation is directly proportional to flammable gas concentration, meaning that 4% vol. cloud is twice smaller than 2% vol. cloud: In reality the correlation between hydrogen gas clouds of various concentrations is more complicated. CFD modeling indicates that 4% vol. cloud is about an order of magnitude smaller that 2% vol. cloud

Key Results Proposed Hydrogen Systems Electrical Classification Distances (fragment): ComponentZone 1 from source Zone 2 from source Comments Any volume of gaseous storage or Hydride storage up to 25 bar zero0.3 m from valves Valves are the only source of leak if vent pipes are discharged at a safe location > 25 bar to <440 bar pressure Up to 250 l water capacity zero0.5 mA leak will be short lived and pressure will reduce quickly > 250 l to 2000 lzero1.2 m horizontal and 2.2 m up Downwind H2 LFL is 4% at 1.14 m Over 2000 l < 8000 l zero1.2 m down and horizontal 2.2 m up Distance equals CFD model 8000 l and overzero2 m horizontal and 3 m up Greater volume has more sites that could leak simultaneously >440 bar pressure 250 l water.5 m1 mDouble the pressure will increase distance 50% > 250 l to 2000 l1 m2 m horizontal and 3.5 m up Mass flow rate will be greater with higher pressure. 1 m zone 1 added due to volume and longer leak duration

Summary Proposed clearance distances are based on CFD modeling results that were obtained based on hydrogen properties and science Proposed clearance distances depend on both storage pressure and storage volume Proposed clearance distances are based on LFL concentration envelopes plus safety factor of 25%