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Lockout / Tagout - Ohio Bureau of Workers' Compensation

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OSHA Standards Interpretation and Compliance Letters<br />

01/05/1998 - Interpretation/variance with the energy isolation<br />

device requirements.<br />

• Record Type: Interpretation<br />

• Standard Number: 1910.147;1910.147(b);1910.147(c)(1)<br />

• Subject: Interpretation/variance with the energy isolation device requirements.<br />

• Information Date:01/05/1998<br />

January 5, 1998<br />

Mr. Richard J. Hackman<br />

The Proctor & Gamble Company<br />

Ivorydale Technical Center<br />

5299 Spring Grove Avenue<br />

Cincinnati, <strong>Ohio</strong> 45217-1087<br />

Dear Mr. Hackman:<br />

This is in response to your November 8, 1996 letter and enclosure, requesting<br />

interpretation/variance with the energy isolation device requirements <strong>of</strong> 29 CFR<br />

1910.147. Please accept our apology for the delay in responding.<br />

In your letter you described a safety disconnect system ("system") which protects<br />

directly wired load circuits to (functionally interconnected) process machines from being<br />

energized by an electrical source. Also, you stated that this system is intended for use<br />

with process machines where it is impractical to provide manually-operated disconnects<br />

at every point <strong>of</strong> access. Further, you disclosed that direct power interruption on the<br />

large drives <strong>of</strong> these process machines is infeasible because the disconnects require a<br />

significant effort to operate, are difficult to position in the (production) line layout, and<br />

are not constructed for frequent use.<br />

As noted in your letter, the safety disconnect system includes the following four basic,<br />

component groups: a power contractor, a control power transformer and fuses, voltage<br />

sensing relays, and a safety lockout switch with verification light. An optional component<br />

is used to establish a required neutral point for the voltage sensing relays, if the power<br />

being monitored is derived from an ungrounded system.<br />

The following system safety features are noted relative to the results <strong>of</strong> the failure<br />

analysis included in your letter:<br />

• The system measures and ensures no motive force to the drive system.<br />

• The system provides fail-safe verification, that is, defaults to the safe position.<br />

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