5. interaction design basics


Working through the accident scenario explain why the various problems arise.

answer available for tutors only

Original text in bold type to aid reading, the expected answer is in normal type. This is a very full answer. This situation mirrors quite closely a mode and closure error in the Excel case study.

Note: Jenny has been 6 hours on a night shift, so errors are likely especially under stress.

1 Jenny notices the core reaction rate has risen very rapidly
one perhaps wonders why this wasn't noticed earlier, perhaps a problem in positioning of displays?

2. she realises she must immediately change the reactor target ...

3. she goes to the Alarm Control Panel … presses '+' twice
Jenny has remembered that she needs to be in RED state to use manual override

4. the Emergency Confirm button glows red
OK, Jenny should press CONFIRM now, but having pressed the '+' and seen the RED alarm state light glow she gets the 'aha' feeling of closure and forgets to press CONFIRM. The red of CONFIRM button is intended to remind her but ...

5. she moves across to the Manual Override panel ...
clearly Jenny didn't notice the CONFIRM button, presumably because it is at the bottom of the panel and she is looking at the Alarm control at the top. Peripheral vision is good at black and white (contrast) changes, but not colour.

6. she selects 'Pressure' from the pull down on the Manual Override panel
which won't work because she is in the wrong Alarm state - this is a mode error caused by the original closure error, but when she is at the far left of the control panel the current system mode (temporary red alarm state) is not visually (or audibly) clear.

7. she types the new value '6000' using the keypad
and forgets to press SET - another a closure error

8. she notices that the number on the Reactor Targets panel has not changed
happily she does double check this rather than simply moving on which would have easily been possible

9. she realises she forgot to press the SET button on the Manual Override panel
OK, realises this one, perhaps because of better logical grouping

10. she presses the SET button
OK, but ...

11. the value still doesn't change
still in wrong mode (alarm state temp red)

12. an automatic audio warning sounds "60 seconds to core meltdown"
good choice of warning modality to use sparingly for critical information. In a big control room a visual alarm would easily be missed.

13. she presses the SET button repeatedly
typical user reaction, happily doesn't cause bad effects!

14. still the value doesn't change
still in wrong mode and despite repeated failure still doesn't think of a mode error - which is normal behaviour in error situations - the expected mode is part of the assumptions she brings to her problem solving

15. she starts again, selects 'Pressure' from the pulldown, types 6000 and presses SET
presumably thinking that the previous part-finished action sequence before 'confused' the system

16. still the value doesn't change
17. the audio warning says "30 seconds to core meltdown"
18. Jenny runs across the room to the Emergency Shutdown panel
no, still doesn't realise that the problem is the wrong alarm state, but now aiming to shut down the reactor to avoid meltdown

19. "20 seconds to core meltdown"
20. she presses "Immediate Emergency Commence" button
correct action in dire emergency

21. the emergency confirm button glows red
but this time is close to the button she has just pressed (in fact it would have already been glowing when she got there but perhaps didn't notice as she was running and stressed) and so this time she notices the CONFIRM button ...

22. "10 seconds to core meltdown"
23. she presses the " Emergency Confirm" button
... at last!

24. she hears the crash of the explosive bolts ...
actually there is nothing quite so good as real physical feedback whether visual, tactile or, as in this case, audible

25. the audio system announces "reactor shutdown successful"
but restarting the reactor will take weeks and cost vast amounts of money!

Other exercises in this chapter

ex.5.1 (tut), ex.5.2 (tut), ex.5.3 (tut), ex.5.4 (tut), ex.5.5 (tut), ex.5.6 (ans), ex.5.7 (tut), ex.5.8 (tut), ex.5.9 (tut), ex.5.10 (tut), ex.5.11 (tut), ex.5.12 (tut)

all exercises for this chapter