Everyday Examples of Mistake-Proofing

Used with permission of author John R. Grout of Berry College, Rome, Georgia.


3.5 inch diskette cannot be inserted unless diskette is oriented correctly. This is as far as a disk can be inserted upside-down.
The beveled corner of the diskette pushes a stop in the disk drive out of the way allowing the diskette to be inserted. This feature, along with the fact that the diskette is not square, prohibit incorrect orientation.


File cabinets can fall over if too many drawers are pulled out.
For some file cabinets, opening one drawer locks all the rest, reducing the chance of the file cabinet tipping.


Fueling area of car has three mistake-proofing devices:
  1. filling pipe insert keeps larger, leaded-fuel nozzle from being inserted
  2. gas cap tether does not allow the motorist to drive off without the cap
  3. gas cap is fitted with ratchet to signal proper tightness and prevent over-tightening.


Automobile controls have a mistake-proofing device to insure that the key is in the on position before allowing the driver to shift out of park. The keys cannot be removed until the car is in park.


Warning lights alert the driver of potential problems. These devices employ a warning method instead of a control method.


Electronic door locks can have three mistake-proofing devices:
  1. insures that no door is left unlocked.
  2. doors automatically lock when the car exceeds 18 miles an hour.
  3. lock won't operate when door is open and the engine is running.


Antilock Braking Systems (ABS) compensate for drivers who stomp on the brake. What used to be a driving error is now the proper braking procedure.


New lawn mowers are required to have a safety bar on the handle that must be pulled back in order to start the engine. If you let go of the safety bar, the mower blade stops in 3 seconds or less. This is an adaptation of the "dead man switch" from railroad locomotives.


Circuit breakers prevent electrical overloads and the fires that result. When the load becomes too great, the circuit is broken.


Even bathroom sinks have a mistake-proofing device. It is the little hole near the top of the sink that helps prevent overflows.


This iron turns off automatically when it is left unattended or when it is returned to its holder.


The window in the envelope is not only a labor saving device. It prevents the contents of an envelope intended for one person being inserted in an envelope address to another.


The dryer stops operating when the door is opened, which prevents injuries.


Automatic light switch in kids' bathroom turns light on automatically. After the bathroom has been unoccupied for a few minutes, the light goes off automatically. The error of forgetting to turn off the light is eliminated.


This wall mounted hair dryer has two slots on either side of the switch. (One slot is partially covered by my thumb.) The bracket on the wall has two pointed prongs that go through the two slots and turn the dryer off if the user neglected to do so.


Parking garages have low clearance. To insure that cars entering the garage will fit, garages are fitted with a go/no-go gauge at the entrance. Hitting the swinging sign or pipe will not damage the vehicle as much as driving into a concrete beam.


Both the sink and the urinal are fitted with light sensors. These sensors insure that the water is turned off in the sink and that the urinal is flushed.


This is an everyday example for me and many other academics, but probably not an everyday example for most people.

The library at Southern Methodist University has a moving shelf system to increase the space utilization. I used to worry that some one would come along and start cranking the shelves and smash me. Luckily, the shelf system designers knew that I would have this fear and installed floor sensors that keep the shelves from moving while someone is stepping on it.


Okay, so this is not an everyday example for anybody. I hope you'll find it interesting nonetheless.
The bathyscaph is a deep water submarine used to explore the very lowest parts of the ocean. It is electrically powered. Once at the bottom, if the batteries or electrical system fail the best outcome would be for the sub to return to the surface. The designers made this outcome occur by holding the ballast in place with electromagnets. When power is lost, the ballast drops off automatically and the sub starts its ascent.