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Ducts utilized to convey hazardous exhaust shall be constructed of approved G90 galvanized sheet steel, with a minimum nominal thickness as specified in Table 18-28-510.8.
Nonmetallic ducts utilized in systems exhausting nonflammable corrosive fumes or vapors shall be listed and labeled. Nonmetallic duct shall have a flame spread index of 25 or less and a smoke-developed index of 50 or less, when tested in accordance with ASTM E 84. Ducts shall be approved for installation in such an exhaust system. Where the products being exhausted are detrimental to the duct material, the ducts shall be constructed of alternative materials that are compatible with the exhaust.
Diameter of Duct or Maximum Side Dimension | Minimum Nominal Thickness | ||
Nonabrasive Materials | Nonabrasive/ Abrasive Materials | Abrasive Materials | |
0 – 8 inches | 0.028 inch (No. 24 Gauge) | 0.034 inch (No. 22 Gauge) | 0.040 inch (No. 20 Gauge) |
9 – 18 inches | 0.034 inch (No. 22 Gauge) | 0.040 inch (No. 20 Gauge) | 0.052 inch (No. 18 Gauge) |
19 – 30 inches | 0.040 inch (No. 20 Gauge) | 0.052 inch (No. 18 Gauge) | 0.064 inch (No. 16 Gauge) |
Over 30 inches | 0.052 inch (No. 18 Gauge) | 0.064 inch (No. 16 Gauge) | 0.079 inch (No. 15 Gauge) |
For SI: 1 inch = 25.4 mm.
(Amend Coun. J. 11-9-16, p. 36266, § 36)