The 6:1 preventive maintenance golden rule

Photo "Maintenance Department Building" courtesy of the U.S. Library of Congress

If 15-30% of the work is reactive, your building is breaking the "world class" benchmark for the PM/CM ratio set in 1979.

The Piper Alpha  preventive maintenance valve disaster, the Alexander L. Kielland cracked and stressed weld disaster, and the AA Flight 191 engine maintenance tragedy are just three examples from our mechanical history showing us that maintenance is critical path to successful, safe operations. The lessons from 1979 extend beyond steps to avoid sad plane crashes–like Flight 191–to useful maintenance strategies that still apply today, and guide building operators to ask themselves “Do my operations meet the “world class” maintenance standard set back then?”

At the time, Alumax¹ of South Carolina was constructing a new plant and it was Mr. John Day, PE, who was in charge of operations. John’s pioneering work earned his plant–and the “maintenance philosophy” he used to run it–awards and recognition from the likes of A.T. Kearney and Maintenance Technology Magazine. Back then, no preventive maintenance software existed, so John commissioned his own system. And nowhere had anyone quantified the key performance indicator benchmarks needed to judge whether or not operations were healthy, so he established them.

preventive maintenance diagram John Day

John Day’s Strategy to Achieve World Class Production Through Reliability

The computer “must supply meaningful and useful information to the user as opposed to normal computer data.”

Interesting ideas rest at the foundation of John’s approach. For his time, a visionary belief that “the computer is the tool to use to accomplish this difficult and complex task.” The belief that maintenance should be treated as an investment rather than a cost, with a positive effect on profitability and a return on investment. John also argues for an expanded view of maintenance, which is not simply to fix, but to preserve from failure and decline. And thankfully, the usefulness of most computer data is a war that has since been won.

The most practical discovery from John’s efforts at that Alumax plant in South Carolina is the “6-to-1” golden rule of preventive maintenance. The guidance is that for every 6 preventive maintenance (PM) measures completed by your building’s technical staff and maintenance vendors, one corrective maintenance (CM) measure should be completed.

Corrective maintenance is the act of performing a repair or adjustment for a condition that was identified during preventive maintenance, and that can’t be reasonably prosecuted while performing the PM activity itself. Emergency work occurs during a downtime event, and may include work requested by building occupants. Both corrective maintenance and emergency work are essentially reactive, while preventive/predictive/preemptive maintenance is essentially proactive. The essence of the art in modulating both sides of this ratio encompasses variables such as how much you trust a given asset to perform as designed and installed, the level of technical complexity of the asset, and what impact would the asset have were it to degrade into a failed state, among others.

A key variable here is the time between PM activities, which should be driven by a confident reading on the mean-time-between-failure for a given piece of equipment. Manufacturer’s specifications, when available, are a great, while conservative, place to start. Rolling your own schedule might involve monthly PM: if after 6, 7, or 8 months no corrective measures are required, the monthly schedule would likely be too frequent. Of course, good PM work order history will guide your operations towards the right periodicity.

Putting this benchmark into practice in your building is an art that requires thoughtful planning, dutiful tracking, tweaks, and an appetite for continuous improvement.

¹Alumax was acquired by Alcoa.

About Millen Paschich

Millen began his career at Cambridge Associates, trained in finance at SMU, and has an MBA from UCLA. Talk to him about bicycling, business, and green chile burritos.

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