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Chapter 19 Risk management 587
Hot standby – where both primary and secondary (backup) systems run simultaneously.
The data are copied to the secondary server in real time so that both systems contain
identical information.
Warm standby – where the secondary system runs in the background to the primary
system. Data are copied to the secondary server at regular intervals, so there are times
when both servers do not contain exactly the same data.
Cold standby – where the secondary system is only called upon when the primary system
fails. The secondary system receives scheduled data backups, but less frequently than in a
warm standby, so cold standby is mainly used for non-critical applications.
Fail-safeing
Poka-yoke
Fail-safeing
The concept of fail-safeing has emerged since the introduction of Japanese methods of
operations improvement. Called poka-yoke in Japan (from yokeru (to prevent) and poka
(inadvertent errors)), the idea is based on the principle that human mistakes are to some
extent inevitable. What is important is to prevent them becoming defects. Poka-yokes are
simple (preferably inexpensive) devices or systems which are incorporated into a process
to prevent inadvertent operator mistakes resulting in a defect. Typical poka-yokes are such
devices as:
● limit switches on machines which allow the machine to operate only if the part is positioned
correctly;
● gauges placed on machines through which a part has to pass in order to be loaded onto,
or taken off, the machine – an incorrect size or orientation stops the process;
● digital counters on machines to ensure that the correct number of cuts, passes or holes
have been machined;
● checklists which have to be filled in, either in preparation for, or on completion of, an
activity;
● light beams which activate an alarm if a part is positioned incorrectly.
More recently, the principle of fail-safeing has been applied to service operations. Service
poka-yokes can be classified as those which ‘fail-safe the server’ (the creator of the service)
and those which ‘fail-safe the customer’ (the receiver of the service). Examples of fail-safeing
the server include:
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colour-coding cash register keys to prevent incorrect entry in retail operations;
the McDonald’s french-fry scoop which picks up the right quantity of fries in the right
orientation to be placed in the pack;
trays used in hospitals with indentations shaped to each item needed for a surgical
procedure – any item not back in place at the end of the procedure might have been left
in the patient;
the paper strips placed round clean towels in hotels, the removal of which helps housekeepers
to tell whether a towel has been used and therefore needs replacing.
Examples of fail-safeing the customer include:
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the locks on aircraft lavatory doors, which must be turned to switch the light on;
beepers on ATMs to ensure that customers remove their cards;
height bars on amusement rides to ensure that customers do not exceed size limitations;
outlines drawn on the walls of a childcare centre to indicate where toys should be replaced
at the end of the play period;
tray stands strategically placed in fast-food restaurants to remind customers to clear their
tables.