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
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
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
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
18. Jenny runs across the room to the Emergency
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"
correct action in dire emergency
21. the emergency confirm button glows
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"
... at last!
24. she hears the crash of the explosive
actually there is nothing quite so good as real physical
feedback whether visual, tactile or, as in this case,
25. the audio system announces "reactor
but restarting the reactor will take weeks and cost
vast amounts of money!