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Accidental Fires Design criteria

Accidental Fires Design criteria. NORSOK STANDARD DESIGN AGAINST ACCIDENTAL LOADS. Design Accidental Actions and associated performance criteria determined by Quantified Risk assessment (QRA) Main safety functions shall not be impaired usability of escape-ways integrity of shelter areas

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Accidental Fires Design criteria

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  1. Accidental FiresDesign criteria

  2. NORSOK STANDARDDESIGN AGAINST ACCIDENTAL LOADS • Design Accidental Actions and associated performance criteria determined by Quantified Risk assessment (QRA) • Main safety functions shall not be impaired • usability of escape-ways • integrity of shelter areas • global load bearing capacity • Integrity normally for et least 1 hour

  3. NORSOK STANDARDRisk acceptance criteria • CharacteristicDesign Accidental Actions corresponding to annual probability of occurrence of ~10-4 per installation • Overall frequency 5·10-4 all accidents often used impairment frequency limit

  4. HC (NPD) 1000 °C ISO Time 1 Hour Fire and Explosion Design Against Accidental Fires often based standard fires • Standard heat fluxes e.g. 100-250 kW/m2 • Fire duration – e.g. 10 min. – 2hrs • Exposed areas – ”envelope” curves Standard heat fluxes Standard Temperature Curves

  5. Example ”traditional” fire scenario: Pool fire from process inventories on cellar deck in 55 minutes

  6. Fire and Explosion Real fires different from standard fires • Fire intensity depends upon amount of combustibles, ”fuel” characteristics, environmental conditions etc. • Heat exposure depends upon location with respect to fire, ”view of fire”... • Transient temperature development in the material is a highly nonlinear process, notably radiation • The structure often possesses considerable reserve strength, i.e. load redistribution upon first member failure  Advanced analysis tools are required

  7. Pressure [bar] 100 30 Time [min] Passive Fire Protection Some Examples Jet Fire • Rupture of a gas pipe, gas ignites. • Pressure drops from 300 bar to “0” within 15min. Thin wall (Sec. Steel) Temp [C] 1000 Thick walll (Main Steel) 30 Time [min] Pressure Typical temperatures of unprotected steel Question: Does this accidental fire cause structural collapse?

  8. Passive Fire Protection Motivation Facts • Temperatures inside or close to fire are approx. 1000-1500ºC • Steel loses strength for temperatures > ~1000 ºC • Aluminum for temperatures > ~3-400 ºC • Unprotected structural components inside fire reach 1000 ºC within minutes: Thin walled members : 3 - 5 min Thick walled members : 5 -15 min Conclusion: Non-redundant Structural Components Exposed to “Offshore” Fires (lasting for more than minutes) need fire protection (f ex. PFP)

  9. Passive Fire Protection Some Examples, cont. Pool Fire • Oil Leakage, oil flows on deck. Ignites. • Deck is unprotected Question: Will the floor beams on the underside of the deck collapse?

  10. Example: Advanced fire scenario HC gas release at riser balcony from production riser. Initial release, 30 kg/s, constant for 5 min., then linearly reducing to 0 at 20 min. Wind: 2 m/s.

  11. Performance Based Design used for Fire • Define functional requirements, (for example 1 hour structural integrity). • Identify accidental events with relevant probability(for example p>10-4) • Compute the fires, the temperature rise in the structure and the structural performance during the fires. • Use international accepted data for the thermal and mechanical properties of the materials, (typically using ISO/Eurocode).

  12. What is possible to simulate in 2005? • Combustion of oil and gas (the chemical reaction), where wind, ventilation, openings, the available Oxygen (O2), production of soot etc are accounted for. • Combustion of oil and gas when the deluge is activated. • The deluge is modeled with the nozzle locations, the droplet size, the amount of water, trigger mechanisms for the deluge (for example radiation level, temperature). • Temperature and radiation on every m2 of the platform • Amount of water [liter per m2 per min] reaching the different surfaces of equipment and structures

  13. What is possible to simulate in 2005? cont’d • Temperature development of insulated components (structures and equipment) including partly protected components and surfaces with damaged PFP. • “Heat Leakage” through openings in insulation (“how fast does the heat flow”?) • Mechanical weakening of steel and aluminum structures and equipment. • Risk for structural collapse, failure of equipment etc. (Will it fail? How close to failure? What is the margins?)

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