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Poka Yoke: The Art of Preventing Errors

Woman smacking her head over making a mistake.

Using Poka Yoke, you can eliminate most of those head-smacking, why-did-we-make-that-mistake process problems.


Let’s face it. Work is often full of busy-work, sometimes it’s monotonous, and there are occasionally days when you head for home and you realize that you just went through the motions all day long (hopefully, you don’t have a lot of those days). Many of the errors in the workplace occur when people are, well, spacing off a little! How can we account for the occasional human lack-of-attention? With a Lean method called Poka Yoke.

Poka Yoke means designing systems to prevent human error, and it can be implemented at any step in any process where errors are likely to be made. A few good examples of Poka Yoke everyone understands include:

Automobile Gas Caps

There are two Poka Yoke applications in most modern gas caps. First, there is a plastic cord that connects the gas cover to the automobile. This prevents those little caps from getting lost. Second, the hole for the gas tank (filling pipe insert) is sized to fit the filling handle of the proper type of fuel  (diesel, leaded, unleaded).

A picture of an automobile gas cap and fuel receptacle

Saving Electricity

Most people remember to turn off lights, turn down the A/C, and otherwise save energy in their own homes. After all, electricity is expensive! But hotels have long known that people do not bring the same conservations to their travel accommodations. So, they poka-yoked a solution.

In many hotels around the world, the hotel room is equipped with a room key holder. If you put your room key in the holder, the lights go on! When you take your room key out and leave the room, the electricity is turned off. Simple solution that prevents the error of wasted energy!

Image of Hotel Key Holder to Control Electricity

Poka Yoke at Work

At its best, Poka Yoke is the elegant work of process ninjas, anticipating the most peripheral of problems and solving them in simple, elegant ways. But we all have to start somewhere, and we don’t need to be ninjas right away. So here are the three basic approaches of Poka Yoke, as defined by Shigeo Shingo of Lean fame.

    • The Contact Method. This is the simplest approach. It is about taking a good look at a product or process and identifying its defects or faults.
    • The Fixed Value Method. Also known as the “Constant Number” method, this method is used when there are a known number of steps that must be done to complete a process. If the person doing the process does not complete the full number of steps, they are alerted that they have missed a step. You encounter examples of the Fixed Value Method when you complete online forms. If you miss a required field, the system refuses to take your submission and highlights the fields that still require information.
    • The Motion Step Method. Also known as the “Sequence Method,” this method is simply about making sure that the process was done correctly. When you document a process, and then use a checklist to ensure that each step of the process is completed, you are using the Motion Step Method.

 

How to Start Using Poka Yoke

You can break all Poka Yoke solutions down into two categories: prevention and detection.  Prevention devices keep a non-conformance from happening, and detection devices alert an operator that a non-conformance has occurred.

A good Poka Yoke device is always simple, and cheap. If they are too complicated, they are not cost-effective and they introduce the possibility of additional non-conformance. Poka Yoke devices should also be completely integrated into the process, and close to where the process occurs. Think about that online form again for a moment. When you complete an online form, you see indications of what fields are required. There may be an asterisk in the box, or the box may be outlined in a different color. This is what we mean by engineering the expectations into the process – the “prevention” form of Poka Yoke. Then, if someone skips a required field, the form may refuse to submit until the field is completed. This is the “detection” form of Poka Yoke. And each of these steps are completely integrated in the process, as well as simple, and cheap.

The 5 Stages of Poka Yoke

Step 1: Remember that everyone makes mistakes. So our job as managers is to create  systems where those mistakes can’t be made.

Any time I hear a senior executive complaining about how people should “just remember” not to make mistakes, I assume a certain lack of self-awareness. We all make mistakes. So the goal isn’t to stop being human, nor is it to only hire people with eidetic memories. People who accept this first concept become the most effective practitioners of Poka Yoke.

Step 2: Find the Root Cause. If we don’t find the root cause, we’ll end up focusing all our energy on symptoms, and implementing several – possibly competing – solutions where only one would do. If you want to learn more about Root Cause Analysis (RCA), check out this article on Root Cause Analysis.

Step 3: Think in terms of Standard Operating Procedures. Every procedure should have a standard operation, it should be documented, and the operators should be trained to it. As long as there is variance in a process, you can’t control for errors.

Step 4: Brainstorm “What Could Go Wrong” for Every Process. This is where the real work of Poka Yoke occurs. When you start thinking about what could go wrong, you start to anticipate – and prevent – the errors.

Step 5: Keep it Simple! When you come up with a way to error proof a process, challenge its complexity. The goal is to use extremely simple, dummy-proof solutions. If you introduce complex ideas, then you are also introducing more opportunities for human error!

Some of the most common Poka Yoke tools and techniques include:

  • Checklists
  • Form/Field Validations
  • Vision Systems (visuals that reinforce the proper result or technique)
  • Blocks, Barrier, and other Safety Features
  • Counters
  • Sensors
  • Alarms
  • Changes in Fixture Designs
  • Changes in Die Designs

First You Solve the Process . . .

People problems are often process problems. What does that mean? It means that we humans are not endowed with perfect memories or perfect consistency. That’s why we must create processes that offset those human characteristics.

There is also a tremendous upside to this. We may not be perfectly consistent or have perfect memories, but we humans are wildly creative, and creativity is the ingredient that brings real value to a company. So, instead of spending our time solving problems and re-doing work, let’s make more time for being creative and bringing value! By using Poka Yoke, we introduce the possibility of more time for more innovation. And that’s exciting, because when we are innovating, the work is never dull, and we never feel the need to go on autopilot.

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