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Carbon Dioxide Systems

Carbon Dioxide Systems

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Carbon Dioxide Systems

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  1. Carbon Dioxide Systems • Carbon dioxide properties • Storage • Uses • Limitations • Types of systems • Local Application • Total Flood

  2. 1. Carbon Dioxide Properties • [.03%] in atmosphere • Colourless, odourless • Density 1.5 times air • Non-conductive • Forms dry ice snow • Displaces oxygen and cools

  3. Phase Diagram • Fig. 7-1, page 115 • Solid phase • Vapour phase • Liquid phase • Triple point • Critical temperature

  4. 2. Storage • High Pressure Cylinders • Low pressure Storage Containers

  5. High Pressure Cylinders • Liquid CO2 • @ 700 F,850 psi, • Can range 32 0F – 120 0F • Capacity, 5- 100 lb • Relief valve, 2500-3,000 psi • Usually matching reserve • Fill density 68% • Dip tube

  6. Low Pressure Storage Containers • Constant O 0F, 300 psi • Refrigerated, pressurized • Electrical supervision • Capacity in tons • Insulated • Pressure relief • multiple discharges possible

  7. 3. Uses • Ordinary combustibles, class A • Flammable liquids, class B • Electrical hazards, class C • See examples in text

  8. 4. Limitations Not with • Oxidizers • Reactive metals • Metal hydrides • Occupied areas

  9. Personnel Hazards • Ideally unoccupied • [CO2] > 34% • [O2] < 15% • Continuous pre-discharge alarms • Breathing apparatus • Voice alarm systems • Exits

  10. Personnel Hazards continued • Signs • Training • Time delay • Manual activation • Manual override • Scented gas

  11. 5. Types of Systems • Total flooding • Local application • Hand hose lines • Standpipe systems and mobile supply

  12. 6. Local Application • Rate-by-volume local application • Rate-by-area local application

  13. Rate-by-volume local application • Imaginary volume • object flush on solid floor • add 2 feet to each open surface Vimg = (L + 4 ft) x ( W + 4 ft) x (H + 2 ft) R = Vimg x ( 1lb/min/ft3) W = R x D

  14. Rate-by-area local application • Pages 127-131 • 2D horizontal fires • flammable liquids • diptanks, drainboards • min. discharge 30 sec. • If storage is high pressure, add 40%

  15. Nozzles • Square coverage • typically 20-30 ft2 • specifications from manufacturer

  16. Steps 1. determine max. width 2. Extend line horizontally to intersect nozzle graph different scales for drainboard and diptank 3. Drop vertical line from point of intersection 4. Extend horizontal line from point of intersection 5. Read flow rate Fliquid (lb/min)

  17. 6. Number of nozzles for diptank Nliquid 7. FRliquid =Nliquid xFliquid 8. Number of nozzles for drainboard Ncoated 9. FRcoated =Ncoated xFcoated 10.FRtotal = Frliquid + Frcoated 11. W (lb) = FR (lb/min) x D (min) 12. If storage is HP, increase FR by 1.4

  18. 7. Total Flood • Multi-step procedure • Evaluate room • Evaluate fire • calculation

  19. Evaluate enclosure integrity • Acoustical ceiling tiles • door closers • Windows • Other openings • Floor openings • Wall joints

  20. Evaluate Enclosure Integrity continued • Wall rigidity • HVAC • Supply shut-off • Exhaust dampers • Fan test

  21. Evaluate Personnel Hazards • Record activity • Time to exit • Worse case time to exit • Door recognition test • Warning sign effectiveness • Review personnel hazards • Don’t increase hazard

  22. Evaluate fire scenario • Control ignition sources • See list pages 133-4 • Surface or deep-seated fire?

  23. Measure room volume • L x W x H • Can reduce for solid objects • Add plenum space

  24. Determine type of combustible • Material • Surface or deep-seated fire

  25. Determine Minimum design concentration • See fig. 7-10 • Theoretical minimum • Minimum design concentration • 34-75%

  26. Determine volume factor • See 7-ll and 7-12 • Lb CO2/ ft 3 • For design conc. = 34% • Varies with room size • Minimum values exist

  27. Determine basic quantity of CO2 • Assumes design conc. = 34 % • Qbasic (lb) = V(ft3) x volume factor (lb/ft3)

  28. Determine material conversion factor • See 7-13 • Dimensionless number • Increases quantity • Materials with design conc. > 34%

  29. Adjust quantity for temperature • 1% increase / 5F0 > 2000F • 1% increase / 1F0 < 00F

  30. Adjust quantity for unclosable openings • Add extra gas • See 7-14 • Need area of opening • Distance center below ceiling

  31. Other scenarios for loss of gas • Supply air • Calculate quantity • Apply flooding factor • Apply material conversion factor • Apply temperature compensation

  32. Consider extended application • For other leaks • Deep-seated fires • Maintain design conc.

  33. Calculate pressure relief venting • Very tight rooms • X = Qtotal / 1.3 P ½ • See 7-15 • unlikely

  34. Determine number of nozzles • One / 400 ft2 ceiling area • Max 20 ft spacing • Max. 10 ft from wall

  35. Calculation form • See page 145