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Technical Note 12

Vapour Cloud Development in Over-filling Incidents

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SUMMARY

This FABIG Technical Note describes an assessment method for calculating the rate at which the volume of a vapour cloud increases during an overfilling incident. The assessment method also gives the concentration of hydrocarbons within the cloud and provides some guidance on the extent of cloud spread in relatively flat sites with the kind of obstructions that would be normal in and around a fuel depot tank farm.

The scope of the HSE VCA method (see HSE Research Report RR908) on which this Technical Note is based has been extended to allow vapour cloud assessment for a range of fuels and solvents that are commonly stored in large volumes. It also gives preliminary guidance on extending the assessment to low (non-zero) wind speeds and to calculate the rate at which a cloud may accumulate in the case of spray releases (e.g. flange failure or pipe rupture).

 

TABLE OF CONTENTS

FOREWORD

CONTENTS

NOTATION

  1. INTRODUCTION
  2. SCOPE
    1. Basic analysis
    2. Extensions to scope (beyond the HSE VCA method)
  3. TECHNICAL BASIS OF THE ASSESSMENT METHOD
    1. Mass entrainment
    2. Concentration of fuel at the tank foot
    3. Additional vaporisation of fine splash products
    4. Near field entrainment
    5. Cloud volume and concentration
    6. Hazard ranges
  4. EXAMPLE CALCULATIONS
    1. Example 1: A gasoline tank similar to Buncefield
    2. Example 2: A large post stabilisation Brent crude tank
    3. Example 3: A ship filled methanol tank
  5. EXTENSIONS IN SCOPE TO WINDY CONDITIONS AND SPRAY RELEASES
    1. Source Term for Windy Conditions
    2. Spray releases
  6. MASS ENTRAINMENT CALCULATIONS
    1. Droplet dynamics and vapour dynamics
    2. Vapour and droplet speeds
  7. SUMMARY
  8. REFERENCES
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Published in: 2013
Keywords:
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