5-4。1 Exhaust Air System。  Provide an exhaust system that captures contaminated air generated during FRP fabrication and repair operations。 Refer to Chapter 2 of this UFC; UFC 3-600-01; NFPA 33, Standard Spray Application Using Flammable and Combustible Materials; NFPA 68, Guide for Venting Deflagrations; NFPA 91,Standard for Exhaust Systems for Air Conveying of Materials; NFPA 654, and the specific requirements of this Chapter。

5-4。2 Hood Design。  The sizes and shapes of work pieces in FRP fabrication and repair facilities vary。 Design separate hoods for processes producing only particulate and only vapor, and both particulate and vapor。 Consider a molding system that completely encloses the work piece if the facility repeatedly manufactures the same work piece。 Design exhaust hoods to enclose all processes to the greatest possible extent without inhibiting operations。 Baffle all exhaust hoods to reduce cross drafts and improve hood efficiency。 Table 5-1 summarizes recommended exhaust hoods, capture velocities, and air pollution control devices for each operation。

Table 5-1。  Recommended Hood, Capture Velocity, and Air Pollution Device

Operation (expected contaminant)

Hood Type Recommended Capture Velocity (m/s (fpm)) Air Cleaning Device

(see notes)

Chemical Mixing (vapors) Workbench (Figure 5-2) 0。51 m/s (100) 1

Lay up (Vapors) Workbench/Floor Exhaust (Figure 5-3) 0。51 m/s (100) 1

Spray up (Vapors) Spray up Booth (Figure 5-4) 0。51 m/s (100) 1

Grind,Cut,Saw (Particulate) Workbench/Floor Exhaust (Figure 5-3) 0。76 m/s (150) 2

Cleanup (Vapors) Ventilated Sink (Figure 5-5) 0。51 m/s (100) 3 or 1

Hand Tools (Particulate) LVHV Vacuum System Not applicable 2

NOTES: (1) Determined by the local air pollution regulatory agency,

(2) fabric collector, and

(3) substitute an aqueous emulsion cleaner for acetone。

5-4。2。1 Plenum Velocity。  Design the plenum velocity at least one-half, but no greater than, the velocity through the perforated plate or layered prefilter to create an even airflow over the hood face。 Design the hood-to-duct transition with an included angle of no more than 90 degrees。

5-4。2。2 Hood Length。  Specify that the length of the hood served by each exhaust plenum will not exceed 2。44 m (8 ft)。 For example, hoods between 2。44 and

4。88 m (8 and 16 ft) in length will have two exhaust takeoffs。 Provide cleanout doors in the plenum to allow removal of accumulated particulate。

5-4。2。3 Portable Hand Tools。  Use portable hand tools with LVHV vacuum systems for sawing, cutting, and grinding on all work pieces。 Ensure that the tools, with their vacuum hoses, are properly sized for the work piece internal angles and curvature。 LVHV systems are described in paragraph 5-4。7。