Mistake-Proofing1It is a common misconception that Mistake Proofing includes any device that simply reduces the possibility of errors.

To help us understand the difference in the principles concerned I am going to use two holiday snaps from my favourite steam railway.

The first is one of the most unusual signs I think you will find at any level crossing. Using a standard warning triangle with an imaginative diagram of a crashing cyclist and two languages, it is designed to warn riders that the up coming rails are hazardous.

Mistake-Proofing2The second, using colour and symbols, shows the safe route to be taken to avoid becoming stuck in the rails on the crossing.

Do they prevent cyclists risking personal injury and damaged equipment? Surprisingly no!

Despite ongoing additions to the warnings, some cyclists either don’t understand or choose to not follow the visual instructions.

This situation is not unique to the railway. In fact any situation where a process can be performed incorrectly is open to improvement. Manufacturing, medical care and information based processes can all benefit from understanding and implementing Visual Management and Mistake Proofing techniques.

Visual Management

Is the application of visual signs, prompts or indicators in order to:

  • Prevent abnormalities occurring by promoting the correct action at the right time
  • Indicate immediately if an abnormality does occur
  • Monitor performance i.e. what has happened, what is happening and what is going to happen

Good visual management needs no interpretation and immediately provokes the correct reaction

The best visual management systems use features such as lights, symbols and standard colour coding. These features, along with optimal positioning, reduce the amount of time it takes a person to correctly interpret what is meant.

All of these good features are present in the railway crossing example, so why doesn’t it work all the time? To understand we need to look at the principles behind Mistake Proofing.

Mistake Proofing

The ultimate goal of Mistake Proofing is to eliminate the wastes associated with errors.

Time, money and resources are wasted wherever errors are allowed to occur and result in defects. (See Shingo’s work).

In our rail crossing example the cyclist has made a process error. He has not followed the procedure indicated by the visual signs and markings.

The resulting defect is the bike trapped in the rails. The rider wastes their own time and money getting free and making repairs as well as passenger time if they delay the train.

Errors must be discovered and eliminated before the opportunity for them to become defects occurs. This is done using a Mistake Proofing device.

These either:

  • Prevent an error being made
  • Detect when an error has occurred as early as possible and feedback into the system to prevent further errors, or correct the error before it becomes a defect

A comparison of the two

Visual Management, often used with 5S and Standardised Work, minimises interpretation, helps ensure consistency and eases completion of a process.

Although Mistake Proofing draws heavily on the techniques of Visual Management, it actually eliminates interpretation and the reliance on familiarity. This eliminates the risk of error.

So the ultimate solution is to design your process, or product, to eliminate the sources of error.

What next at the level crossing?

A prevention device to eliminate the gap between rail and tarmac can be bought.






Ultimately the cost of any Mistake Proofing device must be weighed against the cost of the defects.

Think about what processes you need to improve and whether you need Visual Management or Mistake Proofing.