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<br />e <br /> <br />e <br /> <br />e <br /> <br />of 5 was incorporated into the calculations that follow. Openings on the sides of the building <br />facing the primary direction of velocity flow will add an additional safety factor; however, <br />such openings will tend to be blocked with debris sooner than other openings. <br /> <br />. At least two openings must be included to provide for a safety factor against debris blockage. <br />This safety factor is enhanced when openings are located on at least two different sides of the <br />enclosed area. This will allow fqr more even filling and emptying of the enclosed area and <br />will also reduce the risk of debris being forced against an opening and blocking it. <br /> <br />The fIrst step in determining the total net area required for openings is to calculate the flow rate <br />per square foot of enclosed area, which is based on the rate of rise of the floodwaters. The <br />assumed worst-case rate of rise is 5 feet per hour per square foot of area, or about 0.1 foot per <br />minute. To convert this to gallons per minute per square foot of enclosed area, multiply by a <br />conversion factor of 7.5 gallons per cubic fool. The needed flow rate into the enclosure per <br />square foot of area is then (0.1 foot per minute) times (7.5 gallons per cubic foot), or 0.8 gallon <br />per minute per square foot of enclosed area. The second step is outlined below. <br /> <br />To determine the total net area of the openings, A, needed to permit the above flow rate, <br />the formula is: <br /> <br />Q = 38.OcA(p)5 <br /> <br />Solving for area A and multiplying by a factor of safety: <br /> <br />A = Q (FS) <br />38.0 cp5 <br />where: A is the net area of openings required, in square inches <br /> <br />Q is the flow rate per square foot, which is 0.8 gallon per minute <br /> <br />c is the coefficient of discharge, which is assumed to be 0.2 <br /> <br />P is the pressure, which for one square foot of differential is <br />62.4 pounds per square foot, or 0.4 pound per square inch <br /> <br />FS is the factor of safety, which is 5 <br /> <br />Therefore: <br /> <br />A = 0.8 (5) <br />38.0 x 0.2 x 0.6 <br />= about 1.0 square inch of opening per square foot of enclosed area. <br /> <br />The NFIP <br /> <br />The NFIP was created by Congress in 1968 to provide federally backed flood insurance cover- <br />age, because it was generally unavailable from private insurance companies. The NFIP is also <br />intended to reduce future flood losses by identifying floodprone areas and ensuring that new <br /> <br />9 <br />