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Published May 14, 2018

Many operators will attempt to take advantage of the exception for “minor servicing activities” without having thoroughly evaluated each requirement that must be met in order to truly qualify for it.

    • First, the definition of such activities must be properly understood. In addition to the language in the actual standard, the Compliance Directive for LOTO (CPL 02-00-147) lists “lubricating, draining sumps, servicing filters, making simple adjustments, and inspecting for leaks and/or malfunction” as examples of routine activities which can frequently be done with effective production mode protections like machine guarding. (The Compliance Directive can be found online at
    • Second, the need for equivalent protection must be understood. What is often is overlooked in evaluating that protection is that machine guarding evaluations are typically conducted only with normal operations in mind.  Guards that are perfectly acceptable during normal operations may or may not provide adequate protection during servicing type activities when employees will intentionally place their hands or other parts of their bodies into hazardous areas of the machine.  Typical guards include:


    • Interlocks
    • E-Stops
    • Presence Sensors
    • Light Curtains
    • 2-Hand Activated Push Buttons

OSHA’s CPL 02-00-147 gives a detailed discussion as to how OSHA views these various types of guarding systems, keeping in mind that the key requirement for qualifying for the minor servicing exemption is that the guarding must be “equivalently effective” to locking out the machine.

On page 2-24 of the CPL, OSHA states: “Safeguarding devices (e.g., presence-sensing safeguarding devices) that rely on control circuitry and are used for employee protection purposes may not be used in lieu of LOTO during machine servicing/maintenance activities because control circuit devices are not, by definition, energy isolating devices.”


Further definition of devices that may not be used in lieu of LOTO is found on page 1-5, as follows: “Push-buttons, selector switches, safety interlocks and other control circuit type devices are NOT energy isolating devices. Programmable logic controllers (PLCs) are used in many machine applications, and these control circuit devices are not considered energy isolating devices for purposes of the LOTO standard. Safety functions, such as stopping or preventing hazardous energy (motion), can fail due to component failure, program errors, magnetic field interference, electrical surges, improper use or maintenance, etc.”

So what devices will qualify as providing equivalent protection?  In the CPL, OSHA states that approaches taken in accordance with ANSI standard B11.19 1990 or 2003 – Performance Criteria for Safeguarding will be “considered to have met the requirement for providing effective alternative protection by the use of special tools or guarding (safeguarding) techniques that effectively prevent employee exposure to hazardous energy.” (A detailed discussion of these approaches, with industry-specific examples can be found on pages 3-27 through 3-32.) It also states that these guard devices must be under the exclusive control of the employee performing the minor servicing. Note that this can be complicated if more than one person is working on the minor servicing, and lockout may then be required.

How can you tell fairly easily whether a guard device will meet ANSI B11.19?  Well, if it was installed by anyone other than the machine’s manufacturer, there’s a good chance it won’t.  If it was manufactured prior to 2004, it probably won’t.  Obviously, check the device manufacturer’s literature for certifications, and in the case of emergency stops (e-stops) check specifically for certification as a “fail-safe” device.  While reviewing the manufacturer’s information, it’s also critical to determine what sort of routine inspection, maintenance and servicing they recommend for the device.  Failure to follow those recommendations can mean that the device would no longer be reliable, which could lead to an OSHA violation for not providing equivalent protection, or much more important, to an injury.  How often do clients test their interlocks?

If you can’t find any documentation relating to whether or not a guard meets ANSI B11.19, what other steps can the employer take to determine if it provides the equivalent protection that allows them to take advantage of the minor servicing exemption?  The first thing would be to verify what, if any, hazard an employee could be exposed to during the specific activity being performed. (Note that the use of a tool to reach into the hazard zone can change this part of the analysis.) Then conduct some type of documented failure analysis of the control system that’s being relied on to protect the employee from that hazard.  Techniques could include a Failure Modes and Effects Analysis (FMEA), fault tree analysis, or “what-if” analysis.  There also needs to be an evaluation of whether there are procedures to test if the deactivation that’s being relied on has worked, and whether the guard device is being properly tested and maintained.

If the employer is relying on an e-stop, consider the following:

  • How does it really work, and what does it actually shut off?  Only electrical power, or other potential sources of hazardous energy?  (A surprising number of people don’t really know these details.)
  • If the e-stop button is released, is the machine back in full operational mode, or are additional steps needed to restart it?
  • Is there still exposure to energized electrical circuits after the e-stop has been activated?
  • Is e-stop certified as “fail-safe”?
  • Is an e-stop button truly under the exclusive control of the operator performing the minor servicing activity?
  • If the employer is relying on an interlock, consider the following:
  • Is the interlock certified?  Does it include a “high reliability interlock switch”?
  • Is the interlock properly tested and maintained?
  • Will there be exposed power points?
  • Will there be stored energy/other types of energy?



Taking advantage of the “minor service” exemption to LO/TO is a lot more complicated that it first appears.  And, the reliability and performance of a guarding system needs to be evaluated separately it it’s going to be used to provide an alternative to locking out equipment during minor servicing – the requirements are likely to be much stricter than they would be for normal operation. Our engineers have  understands the regulations and can provide assistance to our clients in avoiding serious injuries and possible OSHA citations.

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