CAPA Corner

Mistake Proofing

By Tom Weaver, Rob Weaver
July 22, 2014


• Categories: 05-Quality/Regulatory, CAPA Corner

During an investigation, once the root cause(s) has been identified, corrective or preventive action is then taken to restore performance to the level it was at before the problem occurred. All root causes fall into one of two categories:

1. A mistake, error, or omission was made. In this situation, mistake proofing techniques are used.
2. There was too much variation in the product, process, or service. Variation reduction and optimization methods are then employed.

In this blog, we’ll explore mistake proofing methods. Mistake proofing is not confined to investigations, but is used in product, process, and service design and development as well as in ongoing operations and improvement applications. The goal with mistake-proofing is to find and correct mistakes, errors, or omissions as close to the source as possible, when the mistakes cost less to correct than if found later. Savvy companies understand that there is a tremendous opportunity if mistake proofing is applied at the time the product, process, or service is designed in order to avoid mistakes during production, service, or customer usage.

The concept of mistake proofing should be imbedded in the culture of the organization. Companies and their people should truly believe that it is not acceptable to allow even a small number of product or service defects. This is not to say that the firm won’t have defects, but that there should be a continuous effort to eliminate as many as possible.

Six mistake-proofing methods

Here are six mistake proofing methods:

1. Eliminate: Make it impossible for the defect to occur by completely eliminating the action or component that causes the mistake. Early in my career I inherited a process to determine if the company was ready to manufacture and market a new product. It was called the “Decision to Market” or “DTM”. This involved circulating a product documentation package to various corporate functions for their review and sign-off. Unfortunately mistakes often occurred: reviewers might take too much time, documentation packages could be misplaced, etc. As a result, products that should have been launched were often significantly delayed and revenues were lost. As part of the investigation we flow charted the entire DTM process and made a list of the DTM requirements that were to be satisfied. We then followed a documentation package through the DTM process and interviewed each person in the process to understand what they were doing. We found several examples where two different reviewers were assuring the exact same requirements were met. This duplication was entirely unnecessary and we were able to eliminate several reviewers from the DTM process and thus reduce the number of errors that could be made!
2. Prevent: Design the product, process, or service so that it is impossible to make the error. An example is configuring the diesel fuel dispensing spout at a gas station so it is too large to insert into an automobile gasoline tank. You would not be able to dispense diesel fuel into a car that operates on gasoline.
3. Replace: Replace the component or action with one that is more error-proof. An example could be replacing a paper form with a computerized form designed to eliminate math errors (such as addition or subtraction errors) and to avoid misplaced forms. Certainly some mistakes or errors could still be made, but the computerized form would be more robust and reliable since adding and subtracting errors would be eliminated and the forms could not be misplaced.
4. Facilitate: Reduce the probability of the mistake. Color coding is an excellent example. Computer systems often come with colored plugs that connect to the same colored receptacles so users don’t make mistakes when setting up their new computers. It might be possible for a red colored plug to be inserted into a blue receptacle, but the probability of that happening has been significantly reduced through color coding.
5. Flag: Flag is another word for inspection. The idea is to find a defect so it can be removed or corrected before it gets to a customer. Ideally the defect is found very close to the point where the mistake is made. The longer it takes to find the defect, additional processing has occurred and the cost of scrapping the item has risen. One example is having the person performing the work to self-inspect that work for errors once the work has been completed. A second example is having the person who next receives that work conduct the inspection. Yet another possibility is having an automated inspection for the defect immediately after the work is done.
6. Mitigate: Reduce the consequences if the defect does occur. One example is establishing a service department to repair product sold to customers if those products have defects. Another is designing redundancy into a product, process, or service to compensate if a mistake occurs. Critical products such as airplanes are designed with back-up systems in case one component or system fails.

Conclusion

Mistakes, errors, and omissions happen! They are made by people every day – the consequences of simply being human. It is a catastrophic blunder to think we can improve by firing and punishing people for being human. Enlightened management understands that mistakes will happen and that management’s responsibility is to build a corporate culture of continuous improvement that includes mistake proofing.