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SPRAY PAINTING
Figure 6.7
Typical water-wash spray booth designs.
The collection efficiency of this one-stage wet scrubber was greater than 90% for particles with a MMAD greater than 2 µ m. The authors stressed the importance of optimizing the spray operating conditions to minimize the generation of mist less than 2 µ m in size. 6.2.2
Airflow
The choice of paint spray booth face velocity and therefore airflow varies with authority; a comparison of the Ventilation Manual and ANSI/OSHA requirements is shown in Table 6.6. The designer is cautioned that these criteria may not be adequate to protect against paint containing heavy metals such as lead and cadmium or catalyst systems used in epoxy or urethane paints. Once the appropriate face velocity is
Table 6.6 Ventilation Requirements per Unit Face Area of Spray Booths cfm/ ft2 (m3/s/m2)
ACGIH
Bench-type spray booth Large spray booth Walk-in Operator outside Autospray paint booth a
ANSI OSHA
Air Spray
Airless
Air Spray
150 a–200 b (0.76–1.02) 100 e (0.51)
100 a–125 b (0.51–0.64) 60 (0.31)
100–150 (0.51–0.75) 100 (0.51)
60–100 (0.31–0.51) 60 (0.31)
150 c–200 d (0.76–1.02) 100 c–150 d (0.51–0.75) 100 c–150 d (0.51–0.75) —
2
2
Airless/ Electrostatic 100 (0.51)
Booth cross section less than 4 ft (0.37 m ). Booth cross section more than 4 ft2 (0.37 m2). c Cross-drafts up to 50 fpm (0.26 m/s). d Cross-drafts up to 100 fpm (0.51 m/s). e 75 fpm (0.38 m/s) for very large, deep booth (operator may require an approved respirator). b
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