DEPARTMENT OF CONSUMER AND INDUSTRY SERVICES  
DIRECTOR'S OFFICE  
OCCUPATIONAL HEALTH STANDARDS  
(By authority conferred on the director of the department of consumer and industry  
services by sections 14 and 24 of 1974 PA 154 and Executive Reorganization  
Orders Nos. 1996-1 and 1996-2, MCL 408.1014, 408.1024, 330.3101, and 445.2001)  
PART 525. GRINDING, POLISHING, AND BUFFING OPERATIONS  
R 325.52501 Scope.  
Rule 1. (1) These rules prescribe the use of exhaust hood enclosures and systems  
in removing dust, dirt, fumes, and gases generated through the grinding, polishing, or  
buffing of ferrous and nonferrous metals.  
(2) These rules replace OH rule 3215.  
History: 2003 AACS.  
R 325.52502 Definitions.  
Rule 2. (1) "Abrasive cutting-off wheels" means organic-bonded wheels, the  
thickness of which is not more than one forty-eighth of their diameter for those up to,  
and including, 20 inches in diameter, and not more than one-sixtieth of their  
diameter for those larger than 20 inches in diameter, used for operations such as cutting,  
cutting off, grooving, slotting, coping, and jointing. The wheels may be any of the  
following:  
(a) "Solid" consisting of organic-bonded abrasive material throughout.  
(b) "Steel centered" consisting of a steel disc with a rim of organic-bonded  
material molded around the periphery.  
(c) "Inserted tooth" consisting of a steel disc with organic-bonded abrasive  
teeth or inserts mechanically secured around the periphery.  
(2) "Belts" means all power-driven, flexible, coated bands used for grinding,  
polishing, or buffing purposes.  
(3) "Branch pipe" means the part of an exhaust system piping that is connected  
directly to the hood or enclosure.  
(4) "Cradle" means a movable fixture, upon which the part to be ground or  
polished is placed.  
(5) "Disc wheels" means all power-driven rotatable discs faced with abrasive  
materials, artificial or natural, and used for grinding or polishing on the side of the  
assembled disc.  
(6) "Entry loss" means the loss in static pressure caused by air flowing into a duct  
or hood. It is generally expressed in inches of water gauge.  
Page 1  
(7) "Exhaust system" means a system consisting of branch pipes connected to hoods  
or enclosures, 1 or more header pipes, an exhaust fan, means for separating solid  
contaminants from the air flowing in the system, and a discharge stack to outside.  
(8) "Grinding wheels" means all power-driven rotatable grinding or abrasive  
wheels, except disc wheels as defined in this standard, consisting of abrasive  
particles held together by artificial or natural bonds and used for peripheral grinding.  
(9) "Header pipe (main pipe)" means a pipe into which 1 or more branch pipes  
enter and which connects such branch pipes to the remainder of the exhaust system.  
(10) "Hoods and enclosures" means the partial or complete enclosure around the  
wheel or disc through which air enters an exhaust system during operation.  
(11) "Horizontal double-spindle disc grinder" means a grinding machine  
carrying 2 power-driven, rotatable, coaxial, horizontal spindles upon the inside ends of  
which are mounted abrasive disc wheels used for grinding 2 surfaces simultaneously.  
(12) "Horizontal single-spindle disc grinder" means a grinding machine carrying  
an abrasive disc wheel upon 1 or both ends of a power-driven, rotatable single  
horizontal spindle.  
(13) "Polishing and buffing wheels" means all power-driven rotatable wheels  
composed all or in part of textile fabrics, wood, felt, leather, paper, and may be coated  
with abrasives on the periphery of the wheel for purposes of polishing, buffing, and  
light grinding.  
(14) "Portable grinder" means any power-driven rotatable grinding, polishing,  
or buffing wheel mounted in such manner that it may be manually manipulated.  
(15) "Scratch-brush wheels" means all power-driven rotatable wheels made from  
wire or bristles and used for scratch cleaning and brushing purposes.  
(16) "Swing-frame grinder" means any power-driven rotatable grinding,  
polishing, or buffing wheel mounted in such a manner that the wheel with its supporting  
framework can be manipulated over stationary objects.  
(17) "Velocity pressure (vp)" means the kinetic pressure in the direction of flow  
necessary to cause a fluid at rest to flow at a given velocity. It is generally expressed in  
inches of water gauge.  
(18) "Vertical-spindle disc grinder" means a grinding machine having a vertical,  
rotatable power-driven spindle carrying a horizontal abrasive disc wheel.  
History: 2003 AACS.  
R 325.52503 Application.  
Rule 3. (1) An employer shall provide suitable hood or enclosures that are  
connected to exhaust systems for every establishment performing dry grinding, dry  
polishing, or buffing.  
(2) Exhaust systems shall be operated continuously whenever operations are  
carried on, and shall be capable of preventing contaminants from entering the breathing  
zone of employees.  
History: 2003 AACS.  
Page 2  
R 325.52504 Hood and branch pipe requirements.  
Rule 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 รท 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  
Over 9 to 16  
Over 16 to  
1 1/2  
2
3
220  
390  
500  
19  
24  
30  
36  
Over 19 to  
Over 24 to  
Over 30 to  
4
5
6
610  
880  
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.  
)
Page 3  
To 9  
Over 9 to 16  
Over 16 to  
2
3
4
300  
500  
610  
19  
24  
30  
36  
Over 19 to  
Over 24 to  
Over 30 to  
5
6
6
740  
1,040  
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)  
Up to 12  
Exhaust Volume  
(feet3/min.)  
220  
Over 12 to 19  
Over 19 to 30  
Over 30 to 36  
390  
610  
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)  
Up to 19  
Exhaust Volume  
(feet3/min.)  
610  
Over 19 to 25  
Over 25 to 30  
Over 30 to 53  
Over 53 to 72  
880  
1,200  
1,770  
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  
Page 4  
Vertical Spindle Disc Grinder  
One-half or  
Disc not  
Nu ust  
more of disc  
covered  
covered  
Disc  
Diameter  
(inches)  
Ex  
Exha  
Num haust  
ber1  
(ft.3/m mber1 (ft.3/min  
in)  
0
)
Up to  
20  
50  
1
2
2
2
2
2
4
5
780  
Over 20  
to 30  
Over 30  
to 53  
Over 53  
to 72  
78  
1,48  
0
0
0
0
1,7  
3,1  
3,53  
6,01  
70  
40  
1Number 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)  
Up to 3  
Exhaust Volume  
(feet3/min.)  
220  
Over 3 to 5  
Over 5 to 7  
Over 7 to 9  
Over 9 to 11  
Over 11 to 13  
300  
390  
500  
610  
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, at a cost as of the  
Page 5  
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.  
History: 2003 AACS.  
R 325.52505 Exhaust systems.  
Rule 5. (1) An employer shall ensure that exhaust systems for grinding,  
polishing, and buffing operations be designed in compliance with American Standard  
Fundamentals Governing the Design and Operation of Local Exhaust Systems, Z9.2-  
1960.  
(2) Exhaust systems for grinding, polishing, and buffing operations shall be tested  
as specified in American Standard Fundamentals Governing the Design and Operation of  
Local Exhaust Systems, Z9.2?1960.  
(3) All exhaust systems shall be provided with suitable dust collectors.  
History: 2003 AACS.  
R 325.52506 Hood and enclosure design.  
Rule 6. (1) It is the dual function of grinding and abrasive cutting-off wheel hoods  
to protect the operator from the hazards of bursting wheels and to provide a means for  
the removal of dust and dirt generated. All hoods  
shall be not less in structural strength than specified in the American National  
Standard Safety Code for the Use, Care, and Protection of Abrasive Wheels, B7.1-1970.  
ANSI B7.1-1970 is adopted by reference in this rule. Printed copies of ANSI B7.1-  
1970 are available from Global Engineering Documents, 15 Inverness Way East,  
Englewood, Colorado 80112, telephone number 1-800-854-7179, website:  
available for inspection at the Michigan Department of Consumer and Industry  
Services, Standards Division, 7150 Harris Drive, P.O. Box 30643, Lansing, Michigan  
48909.  
(2) Due to the variety of work and types of grinding machines employed, hoods  
shall adapt to the particular machine in question, and such hoods shall be located as close  
as possible to the operation.  
(3) Exhaust hoods for floor stands, pedestals, and bench grinders shall be designed  
in accordance with Figure G-2. The adjustable tongue shown in the figure shall be kept  
in working order and shall be adjusted within one-fourth inch of the wheel periphery at  
all times.  
(4) Swing-frame grinders shall be provided with exhaust booths as indicated in  
Figure G-3.  
(5) Portable grinding operations, whenever the nature of the work permits, shall be  
conducted within a partial enclosure. The opening in the enclosure shall not be larger  
than is actually required in the operation and an average face air velocity of not less than  
200 feet per minute shall be maintained.  
Page 6  
(6) Hoods for polishing and buffing and scratch-brush wheels shall be  
constructed to conform as closely to Figure G-4 as the nature of the work will permit.  
(7) Cradle grinding and polishing operations shall be performed with a partial  
enclosure similar to Figure G-5. The operator shall be positioned outside the working  
face of the opening of the enclosure. The face opening of the enclosure should not be  
greater in area than that required for the performance of the operation, and the average  
air velocity into the working face of the enclosure shall not be less than 150 feet per  
minute.  
(8) Hoods for horizontal single-spindle disc grinders shall be constructed to  
conform as closely as possible to the hood shown in Figure G-6. There shall be a  
space between the back of the wheel and the hood, and a space around the periphery  
of the wheel of at least 1 inch to permit the suction to act around the wheel periphery.  
The opening on the side of the disc shall not be larger than is required for the grinding  
operation, but shall not be less than twice the area of the branch outlet.  
(9) Horizontal double-spindle disc grinders shall have a hood encircling the  
wheels and grinding chamber similar to that illustrated in Figure G-7. The openings for  
passing the work into the grinding chamber should be kept as small as possible, but shall  
not be less than twice the area of the branch outlets.  
(10) Vertical-spindle disc grinders shall be encircled with a hood constructed  
so that the heavy dust is drawn off a surface of the disc and the lighter dust exhausted  
through a continuous slot at the top of the hood as shown in Figure G-1.  
(11) Grinding and polishing belt hoods shall be constructed as close to the operation  
as possible. The hood should extend almost to the belt, and 1-inch openings should be  
provided on either side. Figure G-8 shows a typical hood for a belt operation.R  
325.52506 Tables and Charts.  
Page 7  
Page 8  
Page 9