DISCHARGE NOZZLES

Discharge nozzles control the distribution of carbon dioxide into the protected area or onto

the protected equipment (or process). Kidde Fire Systems discharge nozzles are designed to provide the proper combination of flow rate and discharge pattern to protect vital equipment

in a totalflooding manner or on a local application basis.

For total flooding of rooms and large enclosures, types "S" and "M" multijet nozzles are generally used. For total flooding of ducts and small enclosures, the smaller type "V" nozzle may be used.

The number of nozzles required depends on the following considerations:
1. Maximum Spacing: Use 20 foot spacing, as a guide.

2. Flow Rate: The 1/2" "S" and "V" nozzles will discharge up to 120 lb/minute/nozzle. Use the 3/4" "M" nozzle for flow rates in the range from 121 - 250 lb/minute/nozzle.

3. Obstructions: If obstructions within the protected space interfere with the efficient distribution of the carbon dioxide, or lower nozzle flow rates are desired, it may be necessary to increase the quantity of nozzles than initially arrived at when using the maximum spacing and flow rate guidelines.

The type of nozzles selected and their placement shall be such that the discharge will not unduly splash flammable liquids or create dust clouds that might extend the fire, create an explosion, or otherwise adversely affect the contents of the enclosure.*

Example:

Consider a room with dimensions of 10 ft (l) by 20 ft (w) by 10 ft (h). There are two openings

on the wall as shown in figure. A ventilation fan (500 CFM) cannot be shutoff. Enclosure

room temperature of 375°F.

Determine the basic carbon dioxide quantity required to create a 46% by volume concentration. The designed discharge time will be 1 minute.

Ventilation openings
Air outlet near ceiling Area1: 5 ft²
Air inlet centered at 7 ft below ceiling Area 2: 5 ft²

Basic CO2 Quantity Calculation

The volume (V) of the room is: V = 10 ft x 20 ft x 10 ft = 2,000 ft³

Find the required volume factor from Table 3-1, the required volume factor is 18 ft³/lb.

The basic quantity (W1) of CO2: W1 =2,000 / 18 = 112 lb.

Many combustible materials require carbon dioxide concentrations higher than 34% for suppression. For materials requiring a design concentration greater than 34%, the basic quantity of carbon dioxide calculated, using the volume factors shown in Table 3-1, shall be increased by multiplying this quantity by the appropriate material conversion factor (MCF) determined from the curve shown in Figure 3-1.

The basic quantity (BW) of CO2: BW =  W1 x MCF = 112 x 1.5 = 168 lb.

BW = 168 lb.

Un-closable Openings Calculation

Additional CO2 must be provided to compensate for any loss of agent through openings

that cannot be closed prior to or at the start of discharge. The additional quantity shall be equal to the anticipated loss at the design concentration during a one-minute period. This additional quantity of carbon dioxide required shall be discharged through the piping system used to distribute the

basic quantity of agent.

Carbon dioxide will be lost through the bottom opening while air enters through the top opening.

From Figure 3-2 the loss rate will be 17 lb/min · ft² for a concentration of 46 percent at 7 ft.

R =  1/2 x 15 lb/min/ft² x 10 ft² = 75 lb/min
The loss rate would therefore be estimated to be about 75 lb/min.

Based on a 1 minute discharge, the additional CO2 required to compensate for loss through this opening is:
 

LW = 75 lb/min x 1 min = 75 lb.

LW = 75 lb.

Ventilation Calculation

Additional carbon dioxide must be provided for applications where the ventilating system in the protected area cannot be shut off or damped prior to or at the start of discharge. The additional quantity of agent is calculated by dividing the amount of volume moved by the ventilating system during the designed discharge period by the appropriate flooding factor for the enclosure volume from Table 3-1.

The additional quantity of carbon dioxide required to compensate for the continuing ventilation is:

VW = (CFM x t )/volume factor

VW = (500  x 1 )/15 = 34 lb.

VW = 34 lb.

Temperature Correction  Calculation

An additional quantity of carbon dioxide must be provided to compensate for abnormally low or high ambient temperatures. For applications where the normal ambient temperature in the enclosure is above 200°F (93°C) a one-percent increase in the calculated total quantity of carbon dioxide must be provided for each additional 5°F above 200°F (93°C).

For applications where the normal ambient temperature is less than 0°F (-18°C), a one-percent increase in the calculated total quantity of carbon dioxide must be provided for each 1°F below

0°F (-18°C).

The operating temperature exceeds 200°F by a range of: 375°F - 200°F = 175°F
 

The number of 5°F increments in this range is 175°F/5°F = 35

A one-percent increase in the calculated carbon dioxide quantity is required for each 5°F increment, therefore:
 

TCF = 35 x 1% = 35%

TW = (BW  + LW + VW) x TCF

TW = (168 + 75 +34) x 35/100 = 97 lb.

TW = 97 lb.

Total Carbon Dioxide required to protect this enclosure is:

W = BW + LW + VW + TW

W = 168 + 75 + 34 + 97

W = 375 lb. CO2

Volume Factors - Surface Fire

Minimum Design Concentrations

Material Conversion Factor

Leakage Rate

Note: The loss rate shown in the figure is based on assumed 700F (210C) temperature within the enclosure and 700F (210C) ambient outside.