A well-rounded safety professional should be able to systematically communicate the fundamentals of safe machine maintenance. This means being able to:

  • coordinate with electrical engineers and maintenance personnel to oversee the selection of controls, interlocks, and disconnects;

  • evaluate with a vendor why their device does or does not match your safeguarding need;

  • describe for your boss why a safeguard should be purchased;

  • specify to your purchasing agent the exact kind of safety devices needed on a new machine;

  • help a line worker understand how to avoid doing something that could degrade the performance of a machine safeguard.

In this presentation, you will learn why a machine's start and stop control functions are vital for machine risk reduction evaluators to consider, especially as safer machine maintenance becomes a global concern. Specifying machine control devices that fit well with lockout procedures can help prevent an unexpected startup when machine maintenance personnel are in a dangerous location. Workers often forget, or are unaware, that when a jam partially stops a machine, restart may occur the instant the jam is cleared. Start and stop controls take two forms: human-operated devices (push buttons, foot switches, etc.) and built-in, automatic controls (sensors, safety devices, process control interlocks, etc.). The presentation will include: systematic methodology for evaluating sufficiency of safety measures; descriptions of the operating principles of machine safeguards; illustrations of applications they are suited for; and basic design analysis to verify that safeguards are suited for intended applications.

The following terms will be used in the problems presented: (Available in full paper)


The consequences are often grim for maintenance personnel when, in the course of performing machine maintenance tasks, the machine starts up unexpectedly. A recent example illustrates what can happen.

A 44 year-old male maintenance repairman died when a piece of metal struck him in the chest. The victim was working on an ironworker punch press after he removed a jammed piece of metal from the punch assembly. The victim did not follow his employer's policies and procedures when removing the jam. The victim removed the front cover plate of the punch slide assembly without first de-energizing, locking out, or blocking the machine. The machine went through a punch cycle after the victim removed the cover plate. A piece of metal from the punch broke off and struck the victim in the chest. It is not known how the cycle was initiated (FACE, 2000).

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