The Business Case for Efficient Preventive Maintenance

There are two reasons why preventive maintenance (PM) procedures should be well-designed work procedures.

  1. To eliminate the probability of human error in the execution of the procedure.
  2. To improve the wrench time of the workforce.

First, let’s consider the impact human error can have on an organization. The table below shows the probability of human error. According to the chart, a person working independently, under stress, and without a well-defined work procedure is 30,000 times more likely to commit an error than someone who is working with a well-designed procedure and with a team.

Furthermore, when we make errors every day and become accustomed to these errors then these problems become institutionalized losses, as we have made them part of our daily expectations. Well-defined work procedures are intended to eliminate as many of these as possible.



General rate for errors involving very high stress levels


Complicated non-routine task, with stress


Supervisor does not recognize the operator’s error


Non-routine operation, with other duties at the same time


Operator fails to act correctly in the first 30 minutes of stressful emergency situations


Errors in simple arithmetic with self-checking


General error rate for oral communication


Failure to return the manually operated test valve to the correct configuration after maintenance


Operator fails to act correctly after the first few hours in a high stress scenario


General error of omission


General error rate for an act performed incorrectly


Error in simple routine operation


Selection of the wrong switch (dissimilar in shape)


Selection of a key-operated switch rather than a non-key operated switch (EOC)


Human performance limit: single operator


Human performance limit: team of operators performing a well-designed task


Human Error Rates
Source: A Guide to Practical Human Reliability Assessment, by Barry Kirwin

The second reason well-defined work procedures are so important pertains to manpower utilization, namely wrench time. The more comprehensive the job packet, the more efficient the work. There is a lot of value to be gained by an organization for getting the wrench time up.

For example, if an organization has 60 technicians, 15% of the 60 technicians (9) should be working on PM at any given time. If the wrench time for this group of technicians is 29% (North American average) and through better procedures and more complete job packets, the wrench time was shifted to 55% (considered by many to be the upper limit of possibilities), then the organization would effectively realize an 89.65% increase in productivity without hiring any additional personnel.

Some craftsmen have a negative reaction to this line of logic. They believe that doubling the output means they must double their efforts, and the doubled effort is expected at no additional increase in compensation. If these were the only elements in the equation, one could see this as a demotivator. However, more efficient work means easier work.

If I can get better results with less effort, I get an increase in efficiency. The less effort part comes from not looking for parts, not waiting to get a machine down, not waiting for a permit, and not wondering how to do the job or having to invent a way to do the job. A well-constructed job packet contains all these things; therefore, the technician expends less effort while getting more work accomplished. This is wrench time logic that creates a significant portion of the business case for improved PM procedures.


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Allied Reliability provides asset management consulting and predictive maintenance solutions across the lifecycle of your production assets to deliver required throughput at lowest operating cost while managing asset risk. We do this by partnering with our clients, applying our proven asset management methodology, and leveraging decades of practitioner experience across more verticals than any other provider. Our asset management solutions include Consulting & Training, Condition-based Maintenance, Industrial Staffing, Electrical Services, and Machine Reliability.

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