Standard Interpretations - Table of Contents|
| Standard Number:||1910.147|
|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.|
|MEMORANDUM FOR:||MICHAEL G. CONNORS|
|FROM:||PATRICIA K. CLARK, DIRECTOR|
[DIRECTORATE OF ENFORCEMENT PROGRAMS]
|SUBJECT:||Interpretation of "Energy Isolation Device" Application of 1910.147 to Conveyors|
An UPS package jams on the conveyor and other packages quickly begin to pile up. The attendant immediately actuates the stop button at one of the keyed lockout (field station) devices. The conveyor comes to a stop and the attendant climbs aboard the conveyor to free the jammed packages. Lacking the direct control of a manually operated switch or breaker to remove power by disconnecting all power conductors, motor stoppage becomes dependent on the proper functioning of the control circuits. In this case, we assume that the automatic control circuitry in the motor control center malfunctions such that only one phase of the three phase source to the motor is opened (not an uncommon occurrence especially where the over-current protection device opens the third phase (L3) without disturbing the motor starter circuit). Because of the additional load placed on the belt by the jammed packages, the motor, now only operating on two phases, has insufficient torque and stalls, and the belt stops. The attendant, believing that the conveyor has been safely stopped because the maintained stop button on the keyed lockout device was actuated, climbs upon the belt in order to free the jammed parcels. However, as the jam is removed, the resulting load on the conveyor motor is reduced and the belt starts again with sufficient start-up torque from the two remaining phases which have not been disconnected. The attendant becomes unbalanced by the moving conveyor, slips and falls, and is injured.Other scenarios can also be postulated as a result of the lack of effective (positive) energy isolation.
|OSHA Standard||UPS Compliance|
A disconnecting means shall be located in sight from the controller location. (Refer to 1910.305(j)(4)(i) for definition of "In sight from.")
If a motor and the driven machinery are not in sight from the controller location, the installation shall comply with one of the following conditions:
This disconnecting means shall plainly indicate whether it is in the open (off) or closed (on) position.
The disconnecting means shall be readily accessible. If more than one disconnect is provided for the same equipment, only one need be readily accessible.
[Refer to UPS compliance with 1910.305(j)(4)(ii)(a)]
|Standard Interpretations - Table of Contents|
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