Machine Design

The Basics of Lockout/Tagout

Many of the conveyor accidents I discussed in recent Machine Design columns (“Analyzing Conveyor Design for Safety,” Sept. 23, 2010; “When It Comes to Safety, Conveyors are Machines, Too,” Oct. 21, 2010; “Ignorance of Conveyor Hazards Turns Lethal,” Nov. 18, 2010) could have been prevented if the companies and personnel involved had followed OSHA’s Lockout/Tagout (LO/TO) standard, 1910.147. The standard is straightforward, but its details often cause confusion. Two of the most misunderstood sections discuss when LO/TO is needed and which devices are permissible.

Section 1910.147(a)(1)(i) states, “This standard covers the servicing and maintenance of machines and equipment in which the unexpected energization or start-up of the machines or equipment, or release of stored energy could cause injury to employees. This standard establishes minimum performance requirements for the control of such hazardous energy.”

We could certainly discuss many phrases in this paragraph, including what constitutes “maintenance,” what qualifies as “stored energy,” and the extent to which the energy should be controlled. However, the word that is most applicable in most of the LO/TO missteps I see is “minimum.” It’s not enough to follow the letter of the standard; the standard is only a starting point for protecting those working with and near such equipment.

A lesson in adapting the standard to meet workplace needs comes from the hills of Missouri. When the LO/TO standard first came out, one factory’s safety coordinator worried implementing written standards was going to be tough. Most of the company’s maintenance personnel had learned their trade on the family farm and read at a first-grade level.

The coordinator went beyond OSHA’s minimum requirements and created a system that worked for his people. For example, he labeled all the swtiches, hydraulic and pneumatic valves, and blockages used to lock out a punch press 3-GREEN-A-YELLOW. The LO/TO instructions, kept on the supervisor’s desk, used the same labeling system along with photographs, artist renderings, arrows, and easily understood words. He also simplified the LO/TO training in the same manner. The factory easily passed when an OSHA inspector examined their LO/TO performance.

Another common point of misunderstanding comes from section 1910.147(b), which defines some terms used in the standard. Specifically:

“Energy-isolating device. A mechanical device that physically prevents the transmission or release of energy, including but not limited to the following: a manually operated electrical circuit breaker; a disconnect switch; a manually operated switch by which the conductors of a circuit can be disconnected from all ungrounded supply conductors, and, in addition, no pole can be operated independently; a line valve; a block; and any similar device used to block or isolate energy. Pushbuttons, selector switches, and other control-circuit-type devices are not energy-isolating devices.”

Many of my clients ask whether interlocks can be used as lockout devices. Interlocks are control-circuit-type devices, so they cannot be used as lockout devices.

We will look at other aspects of LO/TO next month.

Lanny Berke is a registered professional engineer and Certified Safety Professional involved in forensic engineering since 1972. Got a question about safety? You can reach Lanny at [email protected].

Edited by Jessica Shapiro

© 2011 Penton Media, Inc.

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