Usability disasters

Today is World Usability Day, so I'm going to talk about some famous usability disasters. As web developers we're lucky - our usability shortcomings almost never kill anyone.

Some famous examples of fatal usability problems include:

• The Airbus 320 crash in Jan 1992 was partly caused by a mode switch in the wrong position. The mode switch changed the meaning of descent rate numbers entered into the autopilot and was toggled by a small switch in a large bank of other switches.
• The London Ambulance Service dispatch system that scrolled incoming calls off the the screen before they'd been dealt with (and there was no scroll bar to get them back).
• The Therac-25 radiotherapy machine which killed a number of patients due to unclear error messages. A message like MALFUNCTION 1 or MALFUNCTION 64 was displayed when the machine detected conditions which placed patients at risk, but the meaning of the errors wasn't described in the operators manual.

Can web sites kill people? Flashing content in animated GIFs or video can trigger a seizure in people with photo-sensitive epilepsy. Seizures can be fatal.