APPLICATION METHOD

Choose one of the following approved application methods. Depending on the hazard, it may be nec- essary to combine different application methods on the total system.

Total Flooding

HAZARD VOLUME – Determine the hazard volume by physically measuring the enclosure and calculating its volume. Make a sketch noting any permanent installa- tions that would affect the flow of the agent into the enclosure or affect piping installation. Note any partially enclosed areas that require special consideration to ensure complete flooding of the space. NFPA 12 states “in figuring the net cubic capacity to be protected, due allowance may be made for permanent nonremovable impermeable structures materially reducing the volume.’’

CALCULATING % OF UNCLOSABLE OPENING – The total area of unclosable openings must not exceed 3% of the total hazard area. To calculate the percent of unclosable opening, first total the surface area of the hazard walls, floor, and ceiling. Then total the area of all the unclosable openings. Once both totals have been recorded, divide the total area of all openings by the total area of the hazard and then multiply that number by 100. Total Unclosable Opening Area divided by Total Hazard Area x 100 = % of Unclosable Openings.

The number arrived at will be the percentage of unclosable openings. If the number is above 3%, arrangements must be made to close some of the openings upon discharge of the system.

AGENT QUANTITY – The quantity of agent required for extinguishment is dependent upon whether the fire is a surface-type or deep-seated.

• Surface Fires: It is assumed that extinguishment will occur as soon as the necessary concentration is achieved. Minimum design concentration for many common flammable liquids are given in Figure 1. For materials not listed in this table, values must be obtained from a recognized source or obtained by testing. The minimum design concentration used for any hazard must not be less than 34%.

Minimum Carbon Dioxide Concentrations For Extinguishment

Theoretical Minimum

Min. CO2 Design CO2

Concen- Concen-

Material tration (%) tration (%)

Acetylene 55 66

Acetone 27* 34

Aviation Gas Grades 30 36

115/145 Benzol, Benzene 31 37 Butadiene 34 41 Butane 28 34 Butane-1 31 37 Carbon Disulfide 60 72 Carbon Monoxide 53 64

Coal or Natural Gas 31* 37

Cyclopropane 31 37 Diethyl Ether 33 40 Dimethyl Ether 33 40 Dowtherm 38* 46 Ethane 33 40 Ethyl Alcohol 36 43 Ethyl Ether 38* 46 Ethylene 41 49 Ethylene Dichloride 21 34 Ethylene Oxide 44 53 Gasoline 28 34 Hexane 29 35 Higher Paraffin 28 34 Hydrocarbons Cm H2m + 2m - 5 Hydrogen 62 75 Hydrogen Sulfide 30 36 Isobutane 30* 36 Isobutylene 26 34 Isobutyl Formate 26 34 JP-4 30 36 Kerosene 28 34 Methane 25 34 Methyl Acetate 29 35 Methyl Alcohol 33 40 Methyl Butene – I 30 36

Methyl Ethyl Ketone 33 40

Methyl Formate 32 39

Pentane 29 35

Propane 30 36

Propylene 30 36

Quench Lube Oils 28 34

NOTE: The theoretical minimum extinguishing concentrations in air for the above materials

were obtained from a compilation of Bureau of Mines Limits of Flammability of Gases and Vapors (Bulletins 503 and 627). Those marked with * were calculated from accepted residual oxygen values.

FIGURE 1

6-1

APPLICATION METHOD (Continued) Total Flooding (Continued)

Because some carbon dioxide escapes from the enclosure with the displaced air, the actual amount of agent required is greater than the theoretical amount. For example, to achieve a carbon dioxide concentration of 34% would ideally require about one pound of carbon dioxide per 26 cubic feet of space. However, in actual practice, one pound of carbon dioxide is required per 22 cubic feet of space to achieve 34% concentration. For enclosures of less than 50,000 cubic feet, the minimum quantities of agent and volume factors given in Figure 2 must be adhered to.

Volume Factors

Volume of Volume Factor Calculated

Space (cu. ft. (cu. ft. _{(lb. CO2} Quantity (lb.) inclusive) _{lb. CO2) cu. ft.)} Not Less Than

Up to 140 14 .072 – 141 - 500 15 .067 10 501 - 1600 16 .063 35 1601 - 4500 18 .056 100 4501 - 50000 20 .050 250 Over 50000 22 .046 2500 FIGURE 2

The higher concentration achieved from using this table is based on the assumption that the leakage from a small enclosure will be greater on a volumetric basis, than from a large enclosure. If the minimum design con- centration is greater than 34% for the hazard, the volume factor must be multiplied by the material con- version factor listed in Figure 3 to achieve the required greater concentration.

Material Conversion Factors

FIGURE 3

001858

Special conditions that may occur must be compen- sated for as follows:

– For ventilating systems that cannot be shut down, additional carbon dioxide shall be added to the space through the regular distribution system in an amount computed by dividing the volume moved during the liquid discharge period by the flooding factor. This shall be multiplied by the material conversion factor when the design concentration is greater than 34 percent.

– For extreme temperature conditions, the following compensations must be made:

If the enclosure temperature is above 200 °F (93 °C), the quantity of agent must be increased by 1% for each five degrees above 200 °F (93 °C).

If the temperature is below 0 °F (–17 °C), the agent quantity must be increased by 1% for each one degree below 0 °F (–17 °C).

To calculate the minimum agent quantity required for a total flooding surface fire, complete the following steps: 1. Refer to Figure 1 to determine the correct design concentration for the type of hazard material. Example: A 4500 cubic ft. hazard contains barrels of JP-4 fuel. Referring to the table, JP-4 fuel requires a carbon dioxide concentration of 36%.

2. Refer to the “Volume Factors” in Figure 2. Using the previously calculated hazard volume, determine the required amount of carbon dioxide by dividing the hazard volume (in cubic feet) by the Volume Factor for cu. ft./lb. CO2 (or multiply by lb. CO2/cu. ft.) deter- mined in the table. Example: The sample hazard has a volume of 4500 cubic feet. Dividing 4500 cubic feet by 18 (volume factor) equals 250 lbs. of carbon dio- xide required. If the sample hazard material had re- quired a design concentration of 34%, no additional calculation steps would be required to determine total quantity of carbon dioxide. Because the example hazard requires 36% design concentration, an addi- tional step must be completed to determine amount of carbon dioxide required. Continue with Step 3.

3. For materials requiring a design concentration

greater than 34%, refer to Figure 3. After determining the amount of carbon dioxide required in Step 2, cal- culate the new amount required by following the graph in this figure. Example: The sample hazard contains JP-4 fuel. This fuel requires a design con- centration of 36%. Find 36% on the bottom of the graph. Follow the line up until it intersects with the curved line. At that point, read across to the left to determine the conversion factor. In this case, the conversion factor is 1.1 on the left side of the graph. To complete the calculation, multiply the quantity of carbon dioxide determined in Step 2 (250 lbs.) by the conversion factor of 1.1 which equals 275. There- fore, 275 lbs. is the required amount of carbon dioxide needed for this sample hazard.

MINIMUM DESIGN CO2 CONCENTRATION – %

CONVERSION

6-3

FIGURE 4

001859

•Deep-Seated Fires: For deep-seated fires, the con- centration of agent must be maintained for a sub- stantial period of time, but not less than 20 minutes, to assure extinguishment. This consideration demands that the enclosure be relatively leak proof. Any leakage must be given careful consideration. The agent con- centration is dependent upon the type of combustible material present. See Figure 5 to determine the correct flooding factors for deep-seated fires.

Flooding Factors For Specific Hazards (Deep Seated)

Flooding Factor

Design (cu. (lb.

Concen- ft./lb. _CO2/

trations % _CO2 cu. ft.) Specific Hazard

50 10 .100 Dry electric,wiring insulation hazards in general. Spaces 0-2000 cu ft. 50 12 .083 Spaces greater than 2000 cu ft.

65 8 .125 Record (bulk paper)

storage, ducts, and covered trenches

75 6 .166 Fur storage vaults,

dust collectors

FIGURE 5