Figure 9-3 Drive-through crossdraft paint booth with no Mechanical replacement air

NOTES:

1。 Size each plenum take-off for no more than 2。44 m (8 ft) of plenum width。 Size the exhaust plenum for a maximum plenum velocity of 5。08 m/s (1,000 fpm)。 Size replacement air plenum for a maximum plenum velocity of 2。54 m/s (500 fpm)。

2。 Perforated plate with9。53-mm (3/8-in) holes。 Size open area for an airflow velocity of 10。16 m/s (2,000 fpm) through holes。

9-3。1。2 Paint Spray Booth Exhaust Filtration System。  There are two types of exhaust air filtration systems。 The first type is a water wash system。 A water curtain is created at the exhaust plenum by a pump providing continuous circulation of water。

The second type is a dry filter system, where the exhaust air passes through filter media。  Consider the following。

a。 Do not design or purchase the water wash paint spray booths。 The water wash system requires more energy to operate than the dry filter system。 The wastewater must be treated and the hazardous constituents removed (often at great cost to the generating facility) before it may be discharged to a municipal treatment plant。

b。 Neither water wash nor dry filter filtration systems can reduce the concentration of volatile organic compounds in the exhaust air stream。 Consult the environmental department for controlling volatile organic compounds。

9-3。2 Storage and Mixing Room。  Refer to the ACGIH IV Manual, Paint Mix Storage Room, VS-75-30 for the design of ventilation system。

9-3。3 Paint Mix Hoods。  Figure 9-4 is an example of a workbench and a floor hood designed for paint mixing。 Provide 0。5 m3/s per m2 (100 cfm per square foot) of hood face。

Figure 9-4  Paint mixing hood and work bench

NOTES:

1。 Size each plenum take-off for no more than 2。44 m (8 ft) of plenum width。 Size each plenum for a maximum plenum velocity of 5。08 m/s (1,000 fpm)。

2。 Perforated plate with 9。53 mm (3/8-in) holes。 Size open area for an airflow velocity of 10。16 m/s (2,000 fpm) through holes。

9-4 FANS AND MOTORS。 Use explosion proof motor and electrical fixtures for exhaust fan。 Do not place electric motors, which drive exhaust fans, inside booths or ducts。  See 4-4。2 for more detailed information about fan selection。

9-5 REPLACEMENT AIR。 There is no control over the room temperature or room static pressure for non-mechanical replacement air systems。  Dust from outside

often enters the paint spray booths through cracks and damages the paint finish。 Therefore, provide a mechanical replacement air system to maintain a neutral air pressure inside the booth。 This will prevent dust from entering the paint spray area。 The neutral air pressure will also prevent paint overspray and vapors from escaping the booth and migrating into adjacent work areas。 For paint mixing room replacement air, refer to the ACGIH IV Manual, Paint Mix Storage Room, VS-75-30。

9-5。1 Air Distribution。  Distribution of replacement air within the spray booth is as significant as the average air velocity through the booth。 Distribute the replacement air evenly over the entire cross section of the booth to prevent turbulence or undesirable air circulation。 The preferred means of distributing the replacement air is through perforated plate as shown in Figures 9-1, 9-2, and 9-3。 See paragraph 2-4。5 for additional replacement air design criteria。