NFPA World Safety presentation

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

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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

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Approach

• CFD modeling and thermal effects analysis of
  typical releases under
• Real operating conditions
• Real geometries
• Real ventilation rates (indoor) and wind
  velocities (outdoors)

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Simulation Examples
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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

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Example of Scenarios and Assumptions

• H2 leak rates of 5 and 20 scfm (0.0020 and 0.0079
  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 60079-10)

These clouds touch the ground, which is 3 m
below the leak orifice
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5 and 20 scfm Simulation Results at 400 bars
CFD LFL Vol m3
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Key Differences with IEC 60079-10

• IEC 60079-10 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

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Key Results
Proposed Hydrogen Systems Electrical
Classification Distances (fragment)
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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