Category Archives: Poka-Yoke

designing a “poka-yoke”


As noted in our previous post, poka-yokes are meant to mistake-proof a process. They must be devised to prevent a particular type of error, which is why it is so important to thoroughly study the problem, the process, and the root causes.

Once you have all the facts and data about what goes wrong most frequently, in what way, and why, you can set your collective creative minds to designing a poka-yoke that most effectively and efficiently prevents the most frequent human errors or omissions.

To effectively design a poka-yoke, follow these simple steps.

Include the right people. Often the simplest and most effective poka-yokes are thought of by the people closest to the work.

For example, a port for the dry-docking and repair of supertankers needed to perfectly align the ship, and this was very time consuming and expensive with lots of engineers with sensitive measuring devices. A fellow working at the dock saw all this effort, and suggested a poka-yoke. His idea was that they move his shack to just the right position on the dock to line up with where the ships needed to align, then mount a scope on the shack in just the right position. He would then watch through the scope and tell them when the ship was in the right position.

It can also be helpful to include an outside perspective. Someone not immersed in the work every day may spot opportunities to eliminate problems or difficulties that the people executing the process every day may take for granted. Also, a good poka-yoke can often be created by borrowing from one industry or application to another, so diversity of experience is very useful in mistake-proofing.

Identify the specific mistakes you want to prevent. Poka-yokes are individually designed to prevent a specific mistake. Since you cannot mistake-proof everything at once, you must study the process and gather the data to identify what specific errors to address first.

Explore modifications to the work environment to reduce errors. The Five-S method identifies ways that the environment contributes to errors, often by making it hard to detect when a problem has occurred. Clutter makes it difficult to spot deviations in the location or condition of critical items. Sorting and cleaning help to mistake-proof. A bank greatly reduced the frequency of delays in processing mortgage applications by clearing off all the desks so each desk had only two applications at any one time, the one the processer was working on and one waiting in their in-box. Many organizations have found shadow-boarding ― creating outlines of tools that should be hanging on the board in that place ― to help them reduce time looking for the right tool or errors from using the wrong tool.

Explore modifications to machines or tools. Using jigs and automatic stops are changes to machines that make it much easier to execute the work to specification. Similarly, tools such as Excel are filled with poka-yokes, such as conditional formatting that can be used so that a cell’s color changes when the data in it meets certain criteria such as a date within a certain date range, quantities over a certain level, or even simply a required cell is blank.

The data validation feature is another handy mistake-proofing tool. This lets you prevent the entry of a wrong data type or an invalid name or a quantity that is too high or non-standard. This feature can be set to prevent entry that does not meet certain criteria or merely alert the user to re-examine the entry.

Explore modifications to materials. Changing materials can help to prevent an error or make a mistake readily visible so easy to catch before it causes trouble.

For example, one company gathered data on the types of errors people made on the forms they were using, and then redesigned the forms to make it much more obvious which fields were required and which were not. This greatly reduced the number of forms that had to go back to the customer for rework.

Explore modifications to the process to reduce errors. Changes to the process can be made to catch critical errors at the time they are made. Many hospitals have implemented a pre-surgical process poka-yoke that involves marking the point of incision ― in some cases having the patient sign off on the spot. To prevent the risk of an undiluted medication being delivered to a patient, a hospital changed the process so the medicine was diluted in the pharmacy rather than in the patient’s room.

mistake-proofing with “poka-yokes”


Are you familiar with the term “poka-yoke?”

If so, then you know that a poka-yoke is a specially-designed feature of a process or a product that either prevents common mistakes or catches them before they cause trouble.

Often referred to as “mistake-proofing,” The term comes from the Japanese, meaning “inadvertent error” and “avoidance” and was popularized by the engineer Shingeo Shingo in his crusade to improve quality by eliminating human errors.

We see and use poka-yokes every day. For example, years ago, a dead car battery due to forgetfulness was a common problem. Since then, a poka-yoke was designed to sound a warning bell if the car lights are left on. A “warning” poka-yoke is a big help, but not fool proof. A more powerful poka-yoke has since been built-into newer cars and turns the lights on and off automatically.

Similarly, you see a wire gate swing out of the front of a school bus to guide children safely across the street; you are asked to double-enter a new password to guard against typos; wires are color-coded; highways have rumble strips.

All of these are features of a product or process that were specially designed to reduce the likelihood of a particular human error.

The best poka-yokes are easy to implement and involve inexpensive changes to the materials, tools, environment, or process. They fit the problem so perfectly they seem obvious once they are deployed. These poka-yokes render the specific human error that was targeted for elimination almost impossible to make.

For example, color-coding, redesigning forms, and other changes to the materials you use may reduce human errors. One company reduced accidents by replacing the white work gloves with neon gloves so that people were more aware of the hand position. One financial services company greatly reduced the number of transactions they had to reject due to customer error by analyzing the data, identifying which mistakes were easiest to make, and then redesigning the form to make required fields hard to overlook.

Yet a simple and powerful poka-yoke is almost never the first solution a team comes up with. The best ideas take creativity, collaboration, and the time to press on past the weaker solutions that come to mind first.

Most often, the first idea is one of the following:

(a) ask people to be more careful,

(b) ask management to send an email telling people to be more careful, or

(c) schedule a training session in which people are instructed to, yes, be more careful!

These solutions might help for a little while, but improvement is fleeting. Instead, we must keep brainstorming ideas until we can find a way to inexpensively make it much easier to do the work right or at least automatically alert a person when he or she has just made the mistake.

Here are some categories or types organized in increasing degrees of effective prevention:

  • Job aides are a little less fleeting than exhorting people to be more careful, because these are present at the work site when the work is being done. Examples include: cheat sheets, check lists, laminated guides, photographic work instructions. We’ve all seen and used these. They make it easier to do things right because they aid our memory, if we consult them. Their weakness is that we can forget to consult them especially when we are rushed, tired, or distracted.
  • Situational visual guides are better. When you design a form, design it to draw attention to the key items. If a particular type of transaction or operation requires an extra step that could easily be forgotten, consider using color coding or conditional formatting to highlight the important information. These can be effective and are often very quick and inexpensive to implement.
  • Situational audio alerts can be even better such as alarm bells when you are about to make a mistake. If you were trying to reduce pick and pack errors, you might want to set up a bell that will ring whenever the package weight does not equal the expected weight for the order. This may be a little harder to implement, but in certain environments the audio signal may be much more effective than a visual cue.
  • Automatic guides can reduce mistakes by leading you through the necessary fields or screens of a data transaction, the safest path through the warehouse, or the correct movement under a jigsaw. Automatic guides can often be designed fairly inexpensively, although may require some programming.
  • Automatic controls are the most effective. These are design features that do not allow a certain mistake. For example, a gas cap may be tethered to the car to control against its loss. An automatic shutoff switch will prevent the work from continuing under the wrong conditions. A form requiring a valid entry is used to prevent missing or invalid entries. These generally involve more time and investment to implement, but if the mistakes have serious consequences automatic controls are the best option.

Fortunately there are some proven best-practices for “how to” design the best poka-yokes, and that will be the subject of our next post.