Section 325.52911. Local exhaust hoods and booths.

Mechanical local exhaust ventilation may occur by means of either of the following:

(a)  Hoods. Freely movable hoods intended to be placed by the welder as near as practicable to the work being welded and provided with a rate of airflow sufficient to maintain a velocity in the direction of the hood of 100 linear feet (30 m) per minute in the zone of welding when the hood is at its most remote distance from the point of welding. The rates of ventilation required to accomplish this control velocity using a 3-inch (7.6 cm) wide flanged suction opening are shown in Table 1.

(b)  Fixed enclosure. A fixed enclosure with a top and not less than 2 sides which surround the welding or cutting operations and with a rate of airflow sufficient to maintain a velocity away from the welder of not less than 100 linear feet (30 m) per minute.

TABLE 1
Welding zone (inches from arc or torch)	Minimum airflow 1 (cubic feet/minute)	Duct diameter (inches 2)
4 to 6	150	3
6 to 8	275	3 1/2
8 to 10	425	4 1/2
10 to 12	600	5 1/2
1 When brazing with cadmium-bearing materials or when cutting on such materials, increased rates of ventilation may be required.
2 Nearest half-inch duct diameter based on 4,000 feet per minute velocity in pipe.

History: 2015 AACS.