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System Design
After the risk assessment has been completed, it is necessary to specify the individual requirements of the system with respect to the amount of foam and the number of nozzles required so that a discharge system can be designed. This is carried out with the following steps:
1. Survey the Risk and Measure the Surface Area of the Risk. Consideration should be given to cylinder size, quantity and location, remote actuator requirements and locations, alarm panel location and engine shutdown requirements.
2. Calculate the Surface Area of the risk. The surface area will be the aggregate of the following:
• top surface (L x W) = AA
• side surfaces (L x W x 2) = BB
• front and rear surfaces (W x H x 2) = CC
Total Surface Area = (AA + BB + CC)
If an environment exists where leaking fuels are not naturally drained and captive under engine or equipment, then the surface area of that area must also be added to the design calculation for foam quantity required.
3. Based on the surface area from the above calculations, selection of cylinders, foam quantity and nozzle quantity is now possible.
4. Foam is dispensed at a rate of 4.1 litres per square meter of surface area, thus if the surface area is multiplied by 4.1 we get the total foam requirement for the system. This is multiplied by 50/60 to give a minimum 50 seconds discharge time.
5. Quantity of nozzles is calculated at 0.67 per square meter, thus it is now possible to determine the number of nozzles, the layout, pipe-work requirements and the bill of materials based on these calculations.
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