Some mistakes are essentially meaningless. When we were first married, my wife practiced law using her maiden name of Wolowic, so she adopted the practice of introducing me using my full name: “This is my husband, Ray Floyd.” As a result, many of her professional colleagues who knew her and not me assumed that my last name was also Wolowic and that I had one of those Southern two-part names like Jim-Bob. Because I saw her col- leagues infrequently, for years they would greet me with something like, “Good morning, Ray-Floyd.” Mistakes of that sort are often amusing but generally have no consequences and do not require any resolution.
Other mistakes do carry consequences. In the process industries, those consequences can range from inefficiency to poor product quality to fire and explosion, and perhaps even loss of life. Mistakes with significant consequences merit formal intervention to prevent those possible conse- quences from becoming reality. Providing your team with a good way to avoid the mistake or the consequence that could otherwise arise from the mistake can have real value to your operations.
Key idea: The industrial importance of mistakes is measured not by
the fact that a mistake is possible or even likely, but rather by the poten- tial consequences of the mistake if it occurs. When we are managing mistakes, our real concern is managing the consequences of mistakes rather than the mistakes themselves.
As you deploy this powerful and enjoyable new capability, it is valuable to formalize the understanding that you are not interested in creating an anal-retentive group who worries endlessly about every possible mistake. You are interested in creating a team that can avoid mistakes that have business consequences.
mistake Proofing: Preventing consequences
The new opportunity that poka-yoke presents is to intervene between the occurrence of a mistake or event and the evolution of the mistake into a bad outcome. In that way, the mistake has no consequences and provides a learning opportunity. As the practice of mistake proofing matures, you will find that people who repeatedly experience an intervention immedi- ately after a mistake soon begin to identify and correct future mistakes before they occur. As I write this, my computer constantly tells me when I misspell a word by inserting a red line under it. This allows me to correct it immediately. Repeated intervention of this sort has taught me to spell more words correctly on the first try. As I experience this form of real- time mistake proofing, I learn not to make mistakes. The same thing will happen in your plant.
mistake Proofing Is common knowledge
Separating mistakes into two parts and using the new opportunity pre- sented by that separation to prevent a consequence is a common experi- ence that your people already know well; this makes it easier to introduce it successfully into your plant. Once you explain it, you will find that all your people already know what mistake proofing is and how to use it. All that you need to do is to teach people to recognize existing industrial opportunities to apply this concept and to create new opportunities for themselves where they do not exist today. Although most people already know all that they need to know in order to practice poka-yoke, most sim- ply never think to do so at work.
The concept is simple. My wife and I learned from our mothers (and I suspect that you did as well) that, when you add an egg to a mixture, you break the egg into a separate bowl and examine it before adding it to the mix to avoid the consequence of a bad egg or a piece of broken eggshell spoiling the mix. This practice is common because everyone knows that it is possible to come across a bad egg and, if a bad egg gets into the mix, the whole thing is ruined. They also know that it is easy to stop that from happening. In mistake-proofing terms, this use of an intermediate bowl is described as “physical separation.” It is one of several standard techniques used to prevent a mistake—in this case using a bad egg—from maturing into the bad consequence of ruining the mix. My mother and many others were practicing poka-yoke before Shingo was born!
There are also many well-known commercial examples of poka-yoke that everyone recognizes and understands. Most people are familiar with the events of autumn 1982 when Tylenol packages were poisoned and several people died. That series of events gave rise to the tamper-evident packaging that we find today on most foods and drugs. As with the eggs, tamper-evident packaging is an example of separating events into two parts. In this case, rather than physical separation, the mistake-proofing concept is to provide a “visual signal” that the situation is not as it should be. Tamper-evident packaging is a good example that this technology is useful not just for preventing mistakes but also for enabling your opera- tors to recognize any situation in your plant that is different in some way from what it should be. That capability often has immense value in the process industries.
Tamper-evident packaging is also a good example of the difference in difficulty of actions that makes events apparent in a way that avoids conse- quences after a mistake and the difficulty of attempting to make the mis- takes or events impossible. Tamper-proof packaging that would make it physically impossible to interfere with the product is extremely difficult and expensive. A friend and former director of product development at Procter & Gamble advises that they worked on this problem for a number of years and finally gave it up as impractical.
On the other hand, tamper-evident packaging is often no more diffi- cult or expensive than incorporating a visually apparent plastic band that ensures buyers that the package has not been previously opened. The tam- per-evident system eliminates the need to take the difficult and expensive steps required physically to prevent someone from tampering with the package. As long as it is always evident that a package has been opened, the consumer will reject it in favor of a sealed package and no harm will occur. Because they recognized that there are two separate opportunities to prevent harm, food and drug manufacturers have been able to take the easy and inexpensive route with complete success.