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  • Olga Wolska-Płonka

A lesson on why never to forget about user experience

Three Mile Island, 1979 - a catastrophic nuclear incident! The culprit? Not just human error, but a design flaw that spiralled into chaos. This incident shares a critical lesson for all of us: the significance of user experience.

sprinter ready to run in red tracksuit question marks on the left side

“Thinking about design is hard, but not thinking about it can be disastrous.”

Ralph Caplan

Three Mile Island nuclear power plant, March 28, 1979. A partial meltdown of a reactor - the most serious nuclear accident in the United States. It was rated as a level 5 on the seven-point International Nuclear Event Scale.

What exactly has happened?

Operators tried to fix a blockage in a condensate polisher (filters for cooling water). Blockages are quite common and usually fixed easily, but here, the usual method using compressed air failed, without the operators realising it.

A small amount of water pushed by compressed air forced its way past the check valve and found its way into an instrument air line. This was the cause for pumps shut down late in the night and then to an emergency shutdown.

The mechanical failures were compounded by the initial failure of plant operators to recognise the situation. TMI training and procedures left operators and management ill-prepared for the deteriorating situation.

During the event, these inadequacies were compounded by design flaws, including poor control design, the use of multiple similar alarms, and a failure of the equipment to clearly indicate what was happening and how to prevent it.

But why did this happen?

This accident was described as human error and inadequate staff preparation, as is customary in such cases, but let's take a closer look at what caused this mistake.

The power plant control room resembles a captain's bridge on a ship.

On a massive 25-meter-long control panel, there are numerous buttons and control systems. In total, there were 1,100 knobs and switches, as well as 600 warning lights. During the accident, each of these controls was in alarm mode, accompanied by the continuous wailing of sirens.

Imagine this chaos - all the controls blinking in red, and an unbearable noise surrounds you.

In such an atmosphere, you have to find the correct cause of the problem on an extremely complicated panel. Operators had to additionally consult procedural instructions during the emergency to ensure 100% compliance with the procedures.

The way all these controls interacted and were connected was impossible to comprehend, and the consequences of switching one had a cascade effect in an entirely different part in an unpredictable manner.

The design of the control panel, and human-machine interaction, was truly the cause of the disaster. Designers spent a lot of time designing the controls and their components but paid little attention to envisioning what the working conditions would be like and how the staff would experience it.

What is the lesson for us?

What happened in the described accident is a powerful lesson. The problems faced by operators at the Three Mile Island power plant are very similar to the issues encountered by everyday users of devices or software.

When we design something for people to use, we must try to empathise with what they will do and feel, thereby discovering the internal logic that guides them in a given situation.

The seemingly strangest and most nonsensical human behaviour arises from some cause. When we understand human behaviour, we can design a product that meets their needs, taking into account their thinking and limitations.


Interesting fact:

Don Norman was head of the post-accident investigation committee, which brought to light the issue with the control room design problems.

If you want to get to know more about the accident and importance of UX read his book “The Design of Everyday Things”



User Friendly: How the Hidden Rules of Design Are Changing the Way We Live, Work, and Play, Cliff Kuang, Robert Fabricant


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