Rethinking N+1 Redundancy Design Guidelines in the Public Utility Industry
How often do we challenge long-accepted design practices, especially in the utility industries, such as power, water, and wastewater? In order to do so, we must look outside public utilities and apply lessons from other industries. Airline and auto industries are two that rely less on redundancy by focusing on increasing the reliability of the primary functions and managing the consequences and associated risk of failure.
How the airline industry focused on increasing reliability
The airline industry is traditionally held up as the leader in reliability thinking with its initial application of reliability centered maintenance (RCM), but it has also been in the forefront in design. At one time, cross-Atlantic flights required airplanes with at least four engines. With the increase in the reliability of jet engines, in 1984 it became the norm to fly over the Atlantic with only two engines. How did this happen? The airline industry focused on increasing the reliability of the primary functions (making the protected function more reliable) instead of counting on backup systems. The saving in weight, fuel consumption and maintenance cost led to enormous savings in the airline industry.
The auto industry continues to rethink N+1
Another example is the spare tire in an automobile. For many years, cars carried a full extra spare in case there was ever a flat. Car designers thought of unique ways of storing this tire including in a trunk, outside the back door, and in the undercarriage. Recently, some designers began to question the need for the full spare. How many people ever check their spare anyway?
How many people even know how to change a spare tire anymore? A full spare weighs a lot, takes up space, and can’t be used for long since the spare mileage doesn’t match the mileage of the other tires. Some cars began offering the “Donut Spare” (N +1/2), where the intention was to replace the functionality of the spare, but only for a short time (with reduced speeds) until the main tire could be replaced or repaired. Some cars were fitted with a tube with a solution to temporarily repair the flat tire to allow the driver to drive the car to a safe place to get repaired.
Now, some car companies have totally gotten rid of a spare (N+0) by increasing the reliability of the primary tire with “Run Flat” where you can drive 50 miles on a flat with reduced speeds. The reliability of the primary functions has been increased to levels where people are comfortable tolerating the risk associated with flying or driving without additional redundancy.
Applying these lessons to the utility industry
Why can’t these lessons be applied to the utility industries, like water, electric, and waste water, so there is a focus on increasing the reliability of the primary functions and managing the consequences and associated risk of failure instead of always avoiding risk through relying on redundancy?
Utilities have to adopt more modern thinking to work with the communities they serve by managing risk and adopting different service level expectations. The airline industry is achieving huge savings by changing the N+1 thinking while increasing reliability and reducing risk.
Richard W. Taylor, a Boeing vice president and a former test pilot once said, ''There have been 30 years of progress since the current rules were written; you no longer have to have an airport in the shadow of your wing tip every place you fly.''
If the airline industry can achieve this, every industry with lesser consequences should be able to move in the same direction with much less fear of catastrophic failures. Managing the risk versus avoiding the risk allows for leaner designs, saving money and valuable resources.