carbon dioxide systems

Carbon Dioxide Systems

1. Carbon dioxide properties2. Storage3. Uses4. Limitations5. Types of systems6. Local Application7. Total Flood

1. Carbon Dioxide Properties

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

Phase Diagram

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

2. Storage

• High Pressure Cylinders• Low pressure Storage Containers

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

Low Pressure Storage Containers

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

3. Uses

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

4. Limitations

Not with • Oxidizers• Reactive metals• Metal hydrides• Occupied areas

Personnel Hazards

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

Personnel Hazards continued

• Signs• Training• Time delay• Manual activation• Manual override• Scented gas

5. Types of Systems

• Total flooding• Local application• Hand hose lines• Standpipe systems and mobile supply

6. Local Application

• Rate-by-volume local application• Rate-by-area local application

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

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%

Nozzles

• Square coverage• typically 20-30 ft2 • specifications from manufacturer

1. determine max. width2. Extend line horizontally to intersect nozzle

graph different scales for drainboard and diptank3. Drop vertical line from point of intersection4. Extend horizontal line from point of

intersection5. Read flow rate Fliquid (lb/min)

Steps

6. Number of nozzles for diptank Nliquid

7. FRliquid = Nliquid x Fliquid

8. Number of nozzles for drainboard Ncoated

9. FRcoated = Ncoated x Fcoated

10. FRtotal = Frliquid + Frcoated

11. W (lb) = FR (lb/min) x D (min)12. If storage is HP, increase FR by 1.4

7. Total Flood

• Multi-step procedure– Evaluate room– Evaluate fire– calculation

Evaluate enclosure integrity

• Acoustical ceiling tiles• door closers• Windows• Other openings• Floor openings• Wall joints

Evaluate Enclosure Integrity continued

• Wall rigidity• HVAC

– Supply shut-off– Exhaust dampers

• Fan test

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

Evaluate fire scenario

• Control ignition sources– See list pages 133-4

• Surface or deep-seated fire?

Measure room volume

• L x W x H• Can reduce for solid objects• Add plenum space

Determine type of combustible

• Material• Surface or deep-seated fire

Determine Minimum design concentration

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

Determine volume factor

• See 7-ll and 7-12• Lb CO2/ ft 3

• For design conc. = 34%• Varies with room size• Minimum values exist

Determine basic quantity of CO2

• Assumes design conc. = 34 %• Qbasic (lb) = V(ft3) x volume factor (lb/ft3)

Determine material conversion factor

• See 7-13• Dimensionless number• Increases quantity• Materials with design conc. > 34%

Adjust quantity for temperature

• 1% increase / 5F0 > 2000F• 1% increase / 1F0 < 00F

Adjust quantity for unclosable openings

• Add extra gas• See 7-14• Need area of opening• Distance center below ceiling

Other scenarios for loss of gas

• Supply air• Calculate quantity• Apply flooding factor• Apply material conversion factor• Apply temperature compensation

Consider extended application

• For other leaks• Deep-seated fires• Maintain design conc.

Calculate pressure relief venting

• Very tight rooms• X = Qtotal / 1.3 P ½

• See 7-15• unlikely

Determine number of nozzles

• One / 400 ft2 ceiling area• Max 20 ft spacing• Max. 10 ft from wall

Calculation form

• See page 145