How Do Lean Processes Prevent Human Error?

Scott asked an important question on how lean processes can be used to prevent human errors. The good news is that lean processes not only support quality but they lean cannot function without a strong quality culture and organizational commitment to quality improvement. Scott asked:

As part of the Nuclear support industry our customer base is committed to Human Performance, the elimination of error as it is a natural part of being human but also ensuring that the organization itself is not the cause of creating an environment that contributes to the potential for human error by allowing “Error Precursors” to go unmitigated. I am trying to marry the commitment to lean with the focus on Human Performance. The focus of lean to break down a process to its simplest components to eliminate error and Human Performance to eliminate the precursors of error, the work environment, individual capabilities, task demands, and human nature. Any suggestions? We are looking both as tools to support our overall initiative of ISQO, excellence in Integrity, Safety, Quality and Output.

This is an extremely important considering the industry Scott supports. To review briefly, lean is based on the Toyota Production System model in which the quality culture is one of the two pillars. The other pillar focuses on flexibility and speed through the focus on continuous flow, pull and the balancing of work to takt time (customer demand pace). These two pillars hold up the headstone that is the elimination of waste. The result is performance excellence. Human factors as well as organizational factors are the foundation on which a lean structure is built.

We need to be very careful not to equate lean with eliminating waste, kaizen events, a group of tools such as 5S, kanban, cells and so forth, but as a whole operating system of which safety and quality are integral parts. To understand the interrelationship of the quality pillar to the other elements of the Toyota Production System and lean, we need to consider the following:

  1. The customer will not pay for poor quality
  2. The Just in Time pillar removes inventory and other slack that hides quality problems
  3. The jidoka pillar establishes technical and human systems to build quality in to the process rather than inspect defects out.

We can appreciate the difference when we consider the difference between a defective part that escapes into an automobile and a defective part that escapes into a nuclear power plant. The cost of poor quality for the latter can be disastrously high so we can say that the jidoka pillar of lean is far more important than the Just in Time pillar. Some misunderstand the jidoka pillar to mean only “autonomation” or the autonomous detection and prevention of errors by machine or equipment, but this is false. The origins of the concept of jidoka are in the invention of the automatic loom but as a management philosophy it is all about how the organization views quality. First, there must be a non-negotiable acceptance by everyone of the following:

  • We do not accept bad work
  • We do not do bad work
  • We do not pass on bad work

Few people argue with the “don’t accept, don’t make, don’t pass on” rule but it is a very different thing when it requires you to call out your colleagues, peers or even your boss for bad quality work. You need to have clear and visible standards, a culture that does not assign blame but seeks systemic root causes, and an accepted process of problem escalation. Lacking these organizational and cultural factors, jidoka fails.

Lean processes prevent human error in three basic ways. First, through the design of quality processes including testing for robustness, the creation of standardized work instructions with quality key points and the effective training of the people using a method at least as good as Job Instruction. Second, processes are error-proofed whenever possible. There are various types and degrees of error-proofing. Rather than list them, I will point you to John Grout’s excellent work over the past decade in compiling these great examples of pokayoke (Japanese for error-proofing).
Here is one example of how an error-proofing system works. First, there is a visual display of the standard, in this case a height limit warning.

As we approach our destination, there is a physical limit on height and another visual display. At this point it is still possible to defeat the height limit if you are very determined, with resulting damage to your vehicle.

We arrive at our destination, the warehouse door and once again are greeted by visuals.

The third way lean processes prevent human errors is by inspection. We have to accept that we are not smart enough to overcome the human human ingenuity to make errors, and as a final protection for the customer, we must inspect. Yes, inspection is an important part of the lean system. Inspection may not add value, but it is not a waste. Rather, it is the “non value added” category in between waste and value: it adds no value but worse things would happen if we cut out inspection.

The quality culture at Toyota and other truly lean companies extends beyond manufacturing but the checking of all work and auditing of all processes. This is done through an overlapping and linked series of source, self and successive checks. People check the work before, during and after the process. Managers, group leaders and team leaders not directly involved in the process check on a periodic basis, according to a standard time routine.

The positive act of checking is far more powerful than reinforcing the “don’ts” of prevention. Studies of human psychology has shown that it is harder for people to “don’t” something than for people to “do” something. Do you know how to “don’t do bad work?” There are many ways to do bad work, and you have to avoid all of them. It’s almost futile to ask for this. But if you say “do check incoming material conforms with specification” and “do check that you checked all key points and the end of every cycle” then at least your quality will be as good as your process design, the quality key points, and how often you audit yourself.

We can extend this idea of positive confirmation rather than negative avoidance. Let’s rephrase the “three don’ts of manual work”. In order to avoid human errors we should design all processes to:

Remove choice
= “Don’t choose”. Don’t allow workers to choose between materials, methods or tools by standardizing.

Remove ambiguity = “Don’t search”. Don’t require workers to search for or figure out anything that should be standard.

Remove white spaces = “Don’t turn around”. Don’t allow workers to leave a task unfinished and hand it off to another person. The gaps between operations are opportunities for ambiguity and personal judgment to creep in, resulting in potential human errors.

As we consider possible failure factors during process design, and as errors are inevitably made, the Ishikawa diagram a.k.a. the fishbone diagram a.k.a. cause and effect diagram is a great visualization tool for root cause analysis. Add other factors to the backbone of this fish and then make branches for individual contributors to error conditions, and then take countermeasures one by one.


So that’s a brief summary of how lean processes prevent or at least mitigate human error. A lot has been left out. Please anyone else pitch in and let’s help Scott keep those nuclear reactors running error-free.

6 Comments

  1. Venkatesh Srambikal

    March 28, 2009 - 2:10 pm

    Scott,
    Does your team use FMEA (Failure Mode Effect Analysis ) ?
    The tool can have sub categories where there is an human machine interface.
    I am guessing this tool is already prevalent in your industry.
    -Vic

  2. Joe

    April 7, 2009 - 1:15 pm

    How can lean prevent employees from counting wrong?

  3. Jon Miller

    April 12, 2009 - 6:14 pm

    Hi Joe,
    Assuming your employees know how to count correctly to the appropriate number, you can do several things. Using eggs as an example:
    1. Mistake proofing. If you are counting a quantity such as a dozen eggs, you can make sure that the egg carton is full. A visual check by the person counting will identify the empty slot.
    2. Replace counting with another quantification method. You can use a scale to weigh the egg carton as an extra check to make sure that there is no missing egg.
    3. Triple check. Each person counts the source, self and successive process. Unless NOBODY can count, you will quickly catch errors.
    I hope that helps. What are you trying to count by the way?

  4. Parag Dhakulkar

    July 19, 2009 - 11:02 pm

    Article give true insight to do to prevent human error in process, but how to eliminate human error in inspection activity in (automotive)assembly line under defined takt time.

  5. Risk Assessment

    November 28, 2009 - 3:07 am

    A very interesting concept.Simialr in concept to fault tree analysis for determining the route causes of accidents.

  6. kabilan

    October 11, 2010 - 7:24 am

    hello,
    i hv a problem with my staff, they frequently “overlooked” certain information in Bills Of Laden(B/L)( shipping Procedure)..
    the consequences of overlooking is high as we need to pay penalty as part of making the right amendment. so, how do we improve staff’s focus and most importantly, encouraging them to produce “error free” B/L’s.