Guarding of nonwoven abrasive wheels

April 3, 1981

MEMORANDUM FOR: HAYES BELL
DIRECTOR, TECHNICAL SUPPORT

FROM: BRUCE HILLENBRAND
DEPUTY DIRECTOR, FEDERAL COMPLIANCE
AND STATE PROGRAMS

SUBJECT: Applicability of Abrasive Wheel Machinery
Guarding Requirements to Scotch-Brite Brand Wheels and Brushes Manufactured by the 3-M Company

Problem: This office received a request for evaluation of the subject products. The Scotch-Brite products vary in composition and application. Depending upon the selected unit and/or grade, the products vary from buffing and polishing to grinding applications. The specific applicability of OSHA standards cannot be definitized. During a preliminary evaluation by Joe Bode, a member of my staff, it became apparent that detailed laboratory analysis and evaluation are required before a firm OSHA position regarding the applicability of specific OSHA standards can be formulated.

Purpose: This request is forwarded to the Office of Technical Support for analysis and appropriate laboratory testing and evaluation. Upon conclusion of your actions please forward the results to this office so that an appropriate OSHA Instruction STD can be developed and issued.

Preliminary Analysis: A preliminary analysis and evaluation of Scotch-Brite Wheels and Brushes manufactured by the 3-M Company was conducted. The ANSI B7.1 standard defines an abrasive wheel as a cutting tool consisting of abrasive grains, regardless of type, held together by organic or inorganic bonds. To that extent, the Scotch-Brite wheels conform. However, the ANSI committee expressly states their intended purpose in the Foreword of the ANSI B7.1 standard as: safety and protection devices can and must be used ---- in case of accidental wheel breakage. Therefore, it follows that the ANSI B7.1, standard and the OSHA 29 CFR 1910.215 standard, which was derived from it, are applicable to the 3-M Scotch-Brite products where a hazard from wheel breakage exists.

The 3-M Company has distributed a Safety Information sheet regarding the Scotch-Brite products (copy attached). The company states that: If this product breaks into fragments in operation, there can be serious injury to unprotected eyes and other parts of the body. Recommended personal protection is presented.

The unique nature and the range of products within the Scotch-Brite line, makes it impossible to assume that all unguarded application of the product would subject employees to hazardous exposures. However, it is equally impossible to conclude that the guarding requirements of ANSI B7.1 and 29 CFR 1910.215 would never be applicable. Therefore, where these products are used on unguarded powered machines and employees are alleged to be exposed to a hazard from fragmentation, it is necessary that OSHA require guarding.

In instances where hazardous employee exposure is substantiated, the requirements of 29 CFR 1910.215 should be enforceable together with appropriate portions of 29 CFR 1910.94(b), .132 and .133.

The incoming request for clarification, together with additional information presented by the 3-M Company Technical Information Services Manager is attached.

The Scotch-Brite products vary in rigidity, density, composition, fatigue strength and cyclic life, and in their applications. The density of grinding wheels (Ref. ANSI B7.1-1978, Appendix B, paragraph B.1, Assumptions) is generally assumed to be 0.1 lb/cu in. or 2.77 g/cu cm. The Scotch-Brite materials vary from 0.10 g/cu cm to 0.90 g/cu cm, where the most dense is approximately 1/3 the density of average industrial grinding wheels. The degree of hazard is of course directly related to the mass of the particles, their form factor, and their rigidity for any particular rotational velocity and wheel size.

Wheel breakage or fragmentation flings high velocity particles tangentially from a rotating wheel. Where the particles have significant mass and a definite form, as do fragments from a conventional grinding wheel, circumferential guards provide protection to persons otherwise exposed. Unfortunately, ANSI does not provide any guidance as to what mass (material density) establishes the hazard threshold. Therefore, in order to provide criteria which will permit creditable enforcement actions by OSHA, a proper laboratory analysis and evaluation are desirable.

An issue of noteworthy concern regarding the Scotch-Brite products, is their fatigue characteristics. The company notes that the products are subject to fragmentation. That form of failure is indicative of internal fibers failures brought about from repeated stressing.

Another major concern relative to these products, is the human tissue penatration properties of the fragments when fragmentation occurs.

Should the above concerns be supported by laboratory investigation, then the requirements of 29 CFR 1910.215 can be substantiated and determined to be applicable to specific items and/or grades within the Scotch-Brite line.