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California Mechanical Code (Part 4, Title 24, California Code of Regulations) - page 5 / 49





5 / 49

506.2 – 506.7

and shall not have openings other than those required for operation and maintenance of the system. Ducts constructed of steel shall comply with Table 5-5 or 5-6.


(1) Class 1 product-conveying ducts that operate at less than four (4) inches water column (995.6 Pa) negative pressure and convey noncorrosive, nonflammable, and nonexplosive materials at temperatures not exceeding 250˚F (121˚C) may be constructed in accordance with Tables 6-1, 6-2, 6-3, 6-4, 6-5, 6-7, 6-8, or, with prior approval, UMC Standard No. 6-2.

  • (2)

    Ducts used in central vacuuming systems within a dwelling unit shall be constructed of materials in compliance with the applicable standards referenced in Chapter

    • 17.

      Penetrations of fire-resistive walls, or floor-ceiling or roof-ceiling assemblies shall comply with the Building Code. Copper or ferrous pipes or conduit extending from within the separation between a garage and dwelling unit to the central vacuum unit may be used.

The use of rectangular ducts conveying particulates shall be subject to approval of the building official. The design of rectangular ducts shall consider the adhesiveness and buildup of products being conveyed within the duct.

Aluminum construction may be used in Class 1 duct systems only. The thickness of aluminum ducts shall be at least two Brown and Sharpe gauges thicker than the gauges required for steel ducts set f o r t h i n T a b l e s 5 - 5 a n d 5 - 6 . 5 0 6 . 3 F i t t i n g s . F i t t i n g s i n C l a s s 2 , 3 , a n d 4 s y s t e m s shall be not less than two gauges thicker than the thickness required for straight runs. Flexible metallic duct may be used for connecting ductwork to vibrating equipment. Duct systems subject to wide temperature fluctuations shall be provided with expansion joints.

Branches shall connect to main ducts at the large end of transitions at an angle not exceeding forty- five (45) degrees (0.79 rad).

Except for ducts used to convey noncorrosive vapors with no particulate, accessible cleanouts shall be provided at ten (10) foot (3,048 mm) intervals and at changes in direction. Access openings shall also be provided for access to sprinklers and other e q u i p m e n t w i t h i n t h e d u c t t h a t r e q u i r e s e r v i c i n g . 5 0 6 . 4 E x p l o s i o n V e n t i n g . D u c t s c o n v e y i n g

explosive dusts shall have explosion vents, openings protected by antiflashback swing valves, or rupture



diaphragms. Openings to relieve explosive forces shall be located outside the building. When relief devices cannot provide sufficient pressure relief, ductwork shall be designed to withstand an internal pressure of not less than 100 pounds per square inch (689 kPa).

If a room or building contains a dust explosion hazard that is external to protected equipment, as defined in of NFPA 654, such areas shall be provided with deflagration venting to a safe outside l o c a t i o n . 5 0 6 . 5 S u p p o r t s . S p a c i n g o f s u p p o r t s f o r d u c t s s h a l l not exceed twelve (12) feet (3,658 mm) for eight (8) inch (203 mm) ducts nor twenty (20) feet (6,096 mm) f o r l a r g e r d u c t s , u n l e s s j u s t i f i e d b y t h e d e s i g n . 5 0 6 . 5 . 1 D u c t s u p p o r t s s h a l l b e d e s i g n e d t o carry the weight of the duct half filled with material. Where sprinkler protection is provided in the duct, the hanger’s design shall include the weight of the duct half filled with water or with the material being conveyed, whichever has the higher density. Loads shall not be placed on connecting equipment.

Exception: Where adequate drainage is provided, the weight of the water shall not r e q u i r e c o n s i d e r a t i o n . 5 0 6 . 5 . 2 H a n g e r s a n d s u p p o r t s e x p o s e d t o corrosive atmospheres shall be Type 316 SS or e q u i v a l e n t . 5 0 6 . 5 . 3 T o a v o i d v i b r a t i o n a n d s t r e s s o n t h e duct, hangers and supports shall be securely f a s t e n e d t o t h e b u i l d i n g o r s t r u c t u r e . 5 0 6 . 5 . 4 H a n g e r s a n d s u p p o r t s s h a l l b e d e s i g n e d to allow for expansion and contraction. [NFPA 9 1 : 2 . 5 . 1 t h r o u g h 2 . 5 . 4 ] 5 0 6 . 6 F i r e P r o t e c t i o n . S p r i n k l e r s o r o t h e r

fire-protection devices shall be installed within ducts having a cross-sectional dimension exceeding ten (10) inches (254 mm) when the duct conveys flammable vapors or fumes. Sprinklers shall be installed at twelve (12) foot (3,658 mm) intervals in horizontal ducts and at changes in direction. In vertical runs, sprinklers shall be installed at the top a n d a t a l t e r n a t e f l o o r l e v e l s . 5 0 6 . 7 D u c t C l e a r a n c e s . 5 0 6 . 7 . 1 A l l d u c t w o r k a n d s y s t e m c o m p o n e n t s handling combustible material and operating at less than 140˚F (60˚C) shall have a clearance of not less than 18 inches (46 cm) from combustible construction or any combustible material.

Exception No. 1: When the ductwork system is equipped with an approved automatic extinguishing system designed for the specific hazard, the clearance shall

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