Therefore, design an enclosing hood to reduce ventilation rates and decrease the potential for exposure to a spill during fueling。 Design the hood as illustrated in Figure 4-11。  Specify the following criteria for the refueling hoods。

a。 A 76 mm (3-in) airfoil rotated inward to prevent turbulence and backflow。

b。 Lighting that is vented and flush mounted in the top of the exhaust hood。

c。 Hood that bolts the floor, using a continuous natural rubber gasket on hood bottom to create a seal between the hood and the floor。

Figure 4-11。  MK-48 refueling hood。

4-3。2。6 Ductwork。  Follow criteria as specified in paragraph 2-4。1 for both MK-46 and MK-48 shops and the following:

a。 Fabricate all ductwork in contact with Otto Fuel II vapors with (black) carbon steel。  Require all joints be either butt welds or flanges。

b。 Size the duct to maintain a minimum transport velocity of 12。7 m/s (2,500 fpm)。

4-3。2。7 Fans。  Select fans as specified in paragraph 2-4。2。

4-3。3 Weather Stack Design and Location。  Proper dispersion from the stack is critical because Otto Fuel II exhaust is not filtered。  See paragraph 2-4。3。

4-3。4 Air Cleaning Devices。  Due to the quantities and types of contaminants generated by these processes, there is no requirement for air pollution control equipment。

4-3。5 Replacement Air。  Design replacement air systems to maintain a pressure (relative to the atmosphere) ranging from -5。0 to -14。9 Pa (-0。02 to -0。06 inches wg) in the spaces with a potential for personnel exposure。 Maintain the spaces with a low potential for personnel exposure at a differential pressure ranging from 2。49 to 12。4 Pa (+0。01 to +0。05 inches wg)。

4-3。5。1 Quantity and Distribution。  Distribute air to produce laminar flow of air from supply to exhaust in the workspace。 Use vertical supply distribution method as

shown on Figure 4-12。 Horizontal supply distribution method as shown on Figure 4-13 is adequate if, and only if, all exhaust hoods are located on the wall opposite the supply plenum。  See paragraph 2-4。5 for detailed criteria。

Figure 4-12。  Vertical distribution method。

Figure 4-13。  Horizontal distribution method。

4-3。5。1。1 Vertical Distribution Method。  Design a drop ceiling with perforated plate to form a plenum in accordance with paragraph 2-4。5。2。

4-3。5。1。2 Horizontal Distribution Method。  Design the wall plenum to cover the entire wall opposite the hoods。 Size the open area of the perforated sheet for 10。16 m/s (2,000 fpm) through the holes。  See Figure 4-13 for more details。

4-3。6 Heating and Air Conditioning。 Design heating, air conditioning, and humidity control according to MILHDBK 1003/3。 Temper the replacement air to provide a minimum winter design temperature of 18 oC (65 oF) and a maximum summer design temperature of 24 oC (75 oF), with a maximum relative humidity of 50 percent。 Do not separate the air conditioning system from the replacement air system。 See paragraph 2-6。2 for criteria on heat recovery systems。  Do not re-circulate exhaust air。

4-4 SYSTEM CONTROLS。 Design system controls in accordance with paragraph 2-5 and the following: