Section R. 325.52504 - Hood and branch pipe requirementsRule 4.
(1) An employer shall ensure that hoods connected to exhaust systems be used, and hoods shall be designed, located, and placed so that dust or dirt particles shall fall or be projected into the hoods in the direction of the airflow. Wheels, discs, straps or belts shall not be operated in such manner and in such direction as to cause the dust and dirt particles to be thrown into the operator's breathing zone.(2) Grinding wheels on floor stands, pedestals, benches, and special-purpose grinding machines and abrasive cutting-off wheels shall have not less than the minimum exhaust volumes specified in Table G-4 with a recommended minimum duct velocity of 4,500 feet per minute in the branch and 3,500 feet per minute in the main. The entry losses from all hoods, except the vertical-spindle disc grinder hood, shall equal 0.65 velocity pressure for a straight takeoff and 0.45 velocity pressure for a tapered takeoff. The entry loss for the vertical-spindle disc grinder hood is in Figure G-1. If any wheel is wider than wheel diameters shown in Table G-4, then the exhaust volume shall be increased by the ratio of the new width to the width shown. Example: If wheel width = 4 1/2 inches, then 4.5 / 4 x 610 = 686 (rounded to 690).
Table G-4 Grinding and Abrasive Cutting-off Wheels
| Wheel Diameter (inches) | Wheel Width (inches) | Minimum Exhaust Volume (feet3/min.) |
| To 9 | 1 1/2 | 220 |
| Over 9 to 16 | 2 | 390 |
| Over 16 to 19 | 3 | 500 |
| Over 19 to 24 | 4 | 610 |
| Over 24 to 30 | 5 | 880 |
| Over 30 to 36 | 6 | 1,200 |
(3) Scratch-brush wheels and all buffing and polishing wheels mounted on floor stands, pedestals, benches, or special-purpose machines shall have not less than the minimum exhaust volume specified in Table G-5. Table G-5
Buffing and Polishing Wheels
| Wheel Diameter (inches) | Wheel Width (inches) | Minimum Exhaust Volume (feet3/min.) |
| To 9 | 2 | 300 |
| Over 9 to 16 | 3 | 500 |
| Over 16 to 19 | 4 | 610 |
| Over 19 to 24 | 5 | 740 |
| Over 24 to 30 | 6 | 1,040 |
| Over 30 to 36 | 6 | 1,200 |
(4) Grinding wheels or discs for horizontal single-spindle disc grinders shall be hooded to collect the dust or dirt generated by the grinding operation and the hoods shall be connected to branch pipes having exhaust volumes as specified in Table G-6. Table G-6
Horizontal Single-Spindle Disc Grinder
| Disc Diameter (inches) | Exhaust Volume (feet3/min.) |
| Up to 12 | 220 |
| Over 12 to 19 | 390 |
| Over 19 to 30 | 610 |
| Over 30 to 36 | 880 |
(5) Grinding wheels or discs for horizontal double-spindle disc grinders shall have a hood enclosing the grinding chamber. The hood shall be connected to 1 or more branch pipes having exhaust volumes as specified in Table G-7. Table G-7
Horizontal Double-Spindle Disc Grinder
| Disc Diameter (inches) | Exhaust Volume (feet3/min.) |
| Up to 19 | 610 |
| Over 19 to 25 | 880 |
| Over 25 to 30 | 1,200 |
| Over 30 to 53 | 1,770 |
| Over 53 to 72 | 6,280 |
(6) Grinding wheels or discs for vertical single-spindle disc grinders shall be encircled with hoods to remove the dust generated in the operation. The hoods shall be connected to 1 or more branch pipes having exhaust volumes as specified in Table G-8. Table G-8
Vertical Spindle Disc Grinder
| Disc Diameter (inches) | One-half or more of disc covered | Disc not covered |
| Number1 | Exhaust (ft.3/min) | Number1 | Exhaust (ft.3/min ) |
| Up to 20 | 1 | 500 | 2 | 780 |
| Over 20 to 30 | 2 | 780 | 2 | 1,480 |
| Over 30 to 53 | 2 | 1,770 | 4 | 3,530 |
| Over 53 to 72 | 2 | 3,140 | 5 | 6,010 |
1 Number of exhaust outlets around periphery of hood, or equal distribution provided by other means.
(7) Grinding and polishing belts shall be provided with hoods to remove dust and dirt generated in the operations and the hoods shall be connected to branch pipes having exhaust volumes as specified in Table G-9. Table G-9
Grinding and Polishing Belts
| Belts Width (inches) | Exhaust Volume (feet 3/min.) |
| Up to 3 | 220 |
| Over 3 to 5 | 300 |
| Over 5 to 7 | 390 |
| Over 7 to 9 | 500 |
| Over 9 to 11 | 610 |
| Over 11 to 13 | 740 |
(8) Cradles and swing-frame grinders. If cradles are used for handling the parts to be ground, polished, or buffed, requiring large partial enclosures to house the complete operation, then a minimum average air velocity of 150 feet per minute shall be maintained over the entire opening of the enclosure. Swing-frame grinders shall be exhausted in the same manner as provided for cradles. (See Fig. G-3).(9) If the work is outside the hood, then air volumes shall be increased as shown in American Standard Fundamentals Governing the Design and Operation of Local Exhaust Systems, Z9.2-1960 (section 4, exhaust hoods). ANSI Z9.2-1960 is adopted by reference in this rule. Printed copies of ANSI Z9.2-1960 are available from Global Engineering Documents, 15 Inverness Way East, Englewood, Colorado 80112, telephone number 1-800-854-7179, website: www.global.ihs.com [File Link Not Available], at a cost as of the time of adoption of these rules of $27.00 or is available for inspection at the Michigan Department of Consumer and Industry Services, Standards Division, 7150 Harris Drive, P.O. Box 30643, Lansing, Michigan 48909.Mich. Admin. Code R. 325.52504