- Standard Number:
OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at http://www.osha.gov.
October 22, 1997
Mr. Ronald Karbowski
One New Bond Street
P.O. Box 15006
Worcester, MA 01615-0008
Dear Mr. Karbowski:
This is in response to your April 15 letter and your July 11 telefax which provide additional information. In your April 15 letter you requested interpretation of the machine guarding requirements under §1910.215 with respect to grinding wheels which are constructed of a metal core to which an abrasive rim is affixed. Please accept our apology for the delay in responding. Your scenario and question and our reply follow.
The wheels in question are constructed of a metallic core (most often steel or aluminum) to which is affixed an abrasive rim. The abrasive rims take on various configurations from a single layer fused to the outer rim to a 1/4" (0.635 cm) deep segment of abrasive attached by a high shear strength epoxy. These wheels are operated at speeds up to 30,000 surface feet per minute and higher on machines (according to the manufacturers) that are not designed to contain the entire wheel in the event of a catastrophic failure. However, the probability of a catastrophic failure of the entire wheel (including the metal center) is extremely remote since even at the seemingly high peripheral speeds, the yield strength of the core material is at least twice that of the stresses being applied during grinding. In the case of the single layer product, the probability of the rim separating from the metal center is extremely remote, and even if it did, the mass of the rim would not be such as to compromise the integrity of a conventional guard designed to contain a bonded abrasive wheel. The worst case scenario would be where an epoxy anchored rim segment stripped off, which again would not contain enough mass to compromise the integrity of a conventional guard design.
In paragraph 1910.211(b)(12), a "safety guard means an enclosure designed to restrain the pieces of a grinding wheel and furnish all possible protection in the event the wheel is broken in operation." In the case of the metal center grinder wheel, will the guard be required to contain the entire wheel in the event of failure, or will it be required to contain only the abrasive portion of the wheel that is most vulnerable to failure during use?
The paragraph 1910.211(b)(12) definition of "safety guard" applies to abrasive grinding wheels covered by §1910.215. Metal center grinding wheels are excluded from coverage under §1910.215 by paragraph 1910.215(a)(5). The American National Standard Institute (ANSI) B7.1-1995 which includes safety requirements for the use, care and protection of abrasive wheels covers guarding requirements for metal center abrasive wheels. Workplace metal center grinding wheels which meet ANSI B7.1-1995 safety requirements are deemed in compliance with Occupational Safety and Health Administration safety standards.
Thank you for your interest in employee safety and health. If we can be of further assistance, please contact the Office of General Industry Compliance Assistance, Mr. Ronald J. Davies, telephone # (202) 219-8031, extension 110.
John B. Miles, Jr., Director
Directorate of Compliance Programs