Unearth the answers and solve the causes of human error in your company by understanding the hidden truths in human error rate tables

Improve work quality and job reliability with this fundamental and sound advice on mistake proofing your workplace activities that has been hidden in the human error table for decades.

Human error is natural. It is the result of the human brain’s design and its limitations. We actually need to make mistakes to help us learn. Though human error is inevitable and normal, it does not mean a mistake has to end in failure.



During the 1980s and 1990s investigations were undertaken into the error rate of work. A pattern emerged that identified what needed be done to reduce errors.

The chart below shows the effects of work processes on human error. Once you use task standardization and repetitive application of the standard method there are fewer mistakes.

The journey to quality improvement needs standardisation and systemisation

The simple reality is that you purposefully need to create standardised systems, processes and methods else you will always have high failure rates and poor performance. The typical failure rates in businesses using common work practices range from 10 to 30 errors per hundred opportunities. The best performance possible in well managed workplaces using normal quality management methods are failure rates of 5 to 10 in every hundred opportunities. These outcomes are the natural result of the work quality assurance processes used. Even with highly experienced and able people doing the work you will get excessive rates of failure. Letting people work from experience and knowledge always creates unwanted random variation that too often produces wrong outcomes.

Once you have people working you will get a steady rate of problems being generated—the rate will depend on the quality assurance system you use. Put ten people into the workplace, with each producing 10 errors per hundred opportunities, and give them 100 opportunities each a week to make a mistake and you will on average get a hundred (100) more problems added to your list of troubles week after week after week after week…

Overlayed in the figure below are the various quality management techniques developed over the last few decades. Since the 1920’s, when aircraft manufacturing boomed, there has been great strides made in developing work quality control methods.

From simply using highly skilled people in engineered and designed work processes, like automated production lines, quality management was introduced through quality inspection of completed jobs. Later, statistical control of work processes was added, in which failure rate data was collected and investigated so that the work process design could be corrected and improved. Once the work process design was fine-tuned, improvement efforts focused on building quality into the product, instead of inspecting it in by having it pass set specifications.

Today’s best human error protection solutions let people make mistakes but prevents the mistake from becoming a failure. Call it error proofing, mistake proofing or defect elimination, these methods of human error reduction all recognise that human error regularly happens, but a mistake can be identified and an error does not need to end in failure and trouble.


Understanding the message in human error rate tables1


Human Error Rate Table Content

The human error rate table below is an extract from the reliability engineering course textbook by Dr David J. Smith, ‘Reliability, Maintainability and Risk’. It lists average human failure rates across industry collected during the later-half of the Twentieth Century.

There are many factors that influence the human error rate and the values in the table are only indicative. The accuracy of the list is unimportant: it is the message and solutions in the table that we need to see and understand.

Understanding the message in human error rate tables1
Understanding the message in human error rate tables2

The values are shown as error rates. A value of 0.001 means 1 error per 1000 opportunities. The second value on the list, 0.00001 for overfilling a bath, implies that for every 100,000 baths filled around the world someone will overfill one bath and water will flood onto the floor.

Human error rate tables confirmed that ‘human element’ and ‘human factor’ error is real and unavoidable. We do not perform well when tasks are structured in ways that require great care, and we perform especially badly under complicated non-routine conditions. Add stress into that that mix and you get disaster.

From the research and studies done by the aircraft industry on ‘human factors’ and the ‘human element’ it became clear that people are the greatest remaining cause of failure by far.

The problems we have with our plant and equipment are not plant, equipment or machine problems. Our equipment and machines are fine. Their engineering, the materials-of-construction of their parts and their manufacturing methods are fine. The problems of poor equipment reliability, poor maintenance results and poor production performance are almost entirely due to human errors that happen throughout our companies—from the Boardroom to the Shopfloor.

Currently the only protection against human error is to design and manage our business processes so we protect our machines and businesses from ourselves. The focus to take is clear once you interpret the information contained in human error rate tables.


The Message in the Human Error Rate Tables

Starting at the bottom of the human error table, notice how the error rate drops as we move upward from Complicated non-routine task (1 error in 10), to Routine task with care needed (1 error in 100), Routine simple task (1 error in 1000), and Simplest possible task (1 error in 10,000).

It is clear that whatever can be done to simplify a task and remove complication from it will deliver sure reductions in human failure rates. The right types of changes to make are also hidden in the table.

Note that ‘Read a 5-letter word with poor resolution wrongly’ can be changed from 3 errors per 100, to 3 errors per 10,000 (a 100 times reduction in misreads) by making it into ‘Read 5-letter word with good resolution wrongly’. All you have to do is make sure that your documents are clear and easy to read.

It begs the question of what is the smallest font to use in your documents? Knowing that you will cause 100 times fewer errors with text that is easy for our mind to resolve, would it not make a lot of sense to never use small font ever again; to include colour and font changes so that we encourage our brains to easily resolve written text; to only ever write by hand in block letters and never use running writing; to ban hand-written and verbal instructions and only provide written instructions.

I suggest that the smallest font you should ever use in any document is a 12 point font. I would even accept the argument that 14 point is the smallest font size to use—especially in technical and maintenance documents and for legally binding commercial documents. The human error table makes the right thing to do clearly obvious.

Another common example from industry is ‘Fail to recognise incorrect status in roving inspection’ with an error rate of 1 in 10. In this case the person is intentionally looking for a problem and yet misses the obvious 1 times in 10. But for ‘Wrongly carry out a visually inspection for a defined criterion (e.g. leak)’ the error rate falls to 3 in 1,000. If you get your people to use checklists with specific criteria to check, instead of doing what they can remember to do, you will intentionally have designed your business for some 100 times fewer errors. That is a massively fantastic outcome that every business can gain for very little cost.

You can also see what happens when you add stress into a situation: for ‘Complicated non-routine work’ the failure rate rises from 10 errors per 100 opportunities to 25 per 100 opportunities. The message is always the same when it comes to reducing human error—make things simple and make sure that there is enough time to do the job without undue haste. Once situations get stressful you guarantee huge increases in human failure rates.

The scariest advice of all is contained in the last error rate—‘Fail to act correctly after 1 minute in an emergency situation’—9 errors in 10. Do not have emergencies; because by two minutes into an emergency situation every decision people make will be wrong!

In Australia during the summer of 2009 the Victorian bush fires took 173 lives. It was the most deadly bush fire in Australian history. The people in charge of the response on that terrible day were taken to court. They made some bad decisions during the emergency and people lost their lives. What else would you expect after reading the last line in human error table above. That such a fire would be a disaster was a foregone result because the people in charge had never been in such an emergency—no one in the organisation had ever experienced such a massive fire. I doubt there was anyone on the planet that day who would not have made bad choices if they were in charge of controlling that calamitous fire.


We are all flesh and blood Animals

The situations listed in the human error rate table are the same sorts of mistakes that every human being does. They cannot be stopped by wishing they would not happen. The extent of knowledge, training and level of skill has little to do with the mistakes we make. Human error occurs because we are human beings. We are flesh and bone animals who tire, whose minds wonder and lose concentration, who have varying strengths and stamina, along with numerous other human factor causes of our mistakes.

How often do we see managers and supervisors put their staff into high stress situations and then complain that their people are not up to standard? Every human error rate table tells us that people simply do not perform well if things get difficult, confusing or stressful.

Here at Lifetime Reliability Solutions we turned our efforts to helping people do great work and developed the Accuracy Controlled Enterprise (ACE) work quality assurance method. ACE is based on using the 3Ts (Target, Tolerance, Test) to prevent human error.

We wanted to help managers turn complicated situations into easy and effortless routine by using 3T Standard Operating Procedures (SOPs) to ensure the best performance from their people. If you want to turn complicated tasks into routine simple tasks that hardly ever go wrong, simply write clear and stress-reducing SOPs incorporating the 3Ts, and then train your people to do them systematically. Watch the human error rate fall by 100 to 1000 times less.

You can also get our book on how to write Accuracy Controlled Standard Operating Procedures from the online store.

Human error will never be zero. Human error happens because we are human; it is unavoidable. Yet we also know what to do to reduce the chance of human failure.

My best regards to you,

Mike Sondalini
Managing Director
Lifetime Reliability Solutions