CXS490 CO2

Total Flooding Systems

1

Creation of an inert atmosphere in rooms or other enclosure (oven, ducts, etc.).

Examples of application:• Drying ovens,• Switch-gear rooms,

• Fume exhaust systems,

• Storage rooms, etc.

2

Application

• Calculated volume may be reduced for space occupied by fixed impermeable objects.• Type combustible (fuel) and possibility of potential deep-seated fire• Minimum design concentration. • Range 34% to 75% from table found in NFPA 12.• Volume factor (assumes 34% design concentration) & surface fire.• Minimum quantity require adjustments based on possibility deep seated fire could result, temperature & uncloseable openings.

3

Total Flooding Design

Deduction allowance for fixed objects

In figuring the net cubic capacity to be protected, due allowance permitted to be made for permanent,non-removable, impermeable structures materiallyreducing volume.

4

Deduction

Can use factors in two ways (multiply by smaller or divide by larger factor).

2000 ft3 ---> 20 ft3/lb or 0.05 lb/ft3

W = V x FV = 2000 x 0.050 or 2000 20

Volume factor used to determine the basic quantity of carbon dioxide to protect an enclosure containing a material requiring a design concentration of 34 percent in accordance with the following Tables:

5

Volume Factor

6

Volume Factor - Metric

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Volume Factor - Imperial

As average small space has proportionately more boundary area per enclosed volume than a larger space, greater proportionate leakages are anticipated and accounted for by graded volume factors in the tables.

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Deduction

Formula

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W = V x FV x FC

where:V = Volume (m3 or ft3)FV = volume factor (kg/m3 or lb/ft3)FC = concentration factor

For materials requiring a design concentration over 34 percent, basic quantity of carbon dioxide calculated from the volume factor given in the tables and increased by multiplying quantity by appropriate conversion factor given in the following figure:

10

Material Conversion Factor

11

Minimum Design Concentration

12

Material Conversion Factor

In two or more interconnected volumes where “free flow” of carbon dioxide can take place, the carbon dioxide quantity shall be sum of the quantities calculated for each volume, using its respective volume factor from the tables.

If one volume requires greater than normal concentration, higher concentration shall be used in all interconnected volumes.

13

Interconnected Volumes

14

CO2 Calculation

Space with dimensions of11.43 m long by 10.69 m wideby 2.72 m high is to beprotected by CO2.The operating temperature range is 10 to 40OC.The room contains a process that generatessignificant amounts of Methyl Ethyl Ketone (MEK)& Carbon Disulfide (CS2).Determine the required amount of agent and thenumber of Cylinders.

15

CO2 CalculationReview the fuels & Determine which Minimum DesignConcentration (MDC)to use: MEK is 40 % & CS2 is 72 %.Use MDC of 72 % - meets more stringent requirements.

FV = 0.80 from Chart 2-3.3(b)FC = 3.0 from Figure 2-3.4Cylinder sizes 34, 45 (most common) & 54 kg - Use largest

cylinders

Additional quantities of carbon dioxide shall be provided to compensate for any special condition that can adversely affect extinguishing efficiency.

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Special Conditions

Openings that cannot be closed at time of extinguishment shall be compensated for by addition of a quantity of carbon dioxide equal to anticipated loss at design concentration during a 1-minute period.

This amount of carbon dioxide shall be applied through the regular distribution system.

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Openings

Losses

18

Room 9 ft ceiling

7 ft Door open

Centre above 5.5’

To MDC Line

17 lb/min-ft2

21 ft2 x 17Loss = 357lb/min

For ventilating systems that cannot be shut down, additional carbon dioxide shall be added to space through the regular distribution system in an amount computed by dividing/multiplying volume moved during the liquid discharge period by flooding factor.

This shall be multiplied by material conversion factor when design concentration is greater than 34 percent. 19

VentilationSystems

For applications where the normal temperature of the enclosure is above 200°F (93.3 °C):• 1% increase in calculated total quantity of CO2 provided for

• each additional 5°F (2.77°C) above 200°F (93.3 °C)

20

High Temperature

For applications where the normal temperature of the enclosure is below 0°F (-17.8 °C)• 1% increase in calculated total quantity of CO2 for

• each 1 °F (0.55 °C) below 0°F (-17.8°C).

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Low Temperature

Under normal conditions, surface fires are usually extinguished during the discharge period.

Except for unusual conditions, it will not be necessary to provide extra carbon dioxide to maintain the concentration.

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Surface Firew

If a hazard contains a liquid having an auto-ignition temperature below its boiling point, then CO2

concentration shall be maintained for a period sufficient for liquid temperature to cool below itsauto-ignition temperature.

23

Hazard Cooling

A minimum flooding factor of 8 ft3/lb (0.22 m3/kg) is used in ducts and covered trenches.

If combustibles represent a deep-seated fire more CO2 will be required to meet deep seated fire requirements.

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Ducts & Trenches

CO2 RequirementsDeep-Seated Fires

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Quantity of carbon dioxide for deep-seated-type fires is based on fairly tight enclosures.

After the design concentration is reached, concentration shall be maintained for a substantial period of time, but not less than 20 minutes.

Any possible leakage shall be given special consideration because no allowance included in basic flooding factors.

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Maintain Concentration

For combustible materials capable of producingdeep-seated fires, required CO2 concentrations cannot be determined with the same accuracy possible with surface burning materials.

Extinguishing concentration varies with mass of material present because of thermal insulating effects.

Flooding factors determined on basis of practical test conditions.

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Flooding Factors Outline only

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Flooding Factors Outline only

Minimum design rate of application based on quantity of carbon dioxide & maximum time to achieve design concentration

For surface fires, design concentration shall be achieved within 1 minute from start of discharge.

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Design Rate Outline only

For very tight enclosures, necessary area of free venting calculated from following:

30

Venting Outline only

Satisfactory results will usually be achieved by assuming expansion of CO2 at 9 ft3/lb (0.56 m3/kg).

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Acceptable ResultsOutline

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Strength & PressureOutline / Overview