On Jan 25, 1:16*pm, (Cynic) wrote:
On Tue, 24 Jan 2012 20:25:07 +0000, Steve Walker

wrote:
I can give you an actual example of the problems. My parents' next-door
neighbour suffered from emphysema. He spent his final years at home,
hooked up to a machine that fed him oxygen enriched air. If the power
failed, the battery would last only a short time and the back-up was
bottled oxygen, which would also work if the machine failed in any other
way. However, he was physically unable to turn the oxygen bottle on by
himself. His wife very rarely spent more than a very short time out of
the house because of this, but had to take a chance occassionally. At
one stage she dared not leave the house at all for a fortnight, as cable
TV was being put in through the area and they had twice hit power cables
- without her there, this could have killed him.

If his wife particularly *needed* to leave him for longer than the
battery would last, she would undoubtedly arrange for a more robust
backup system. *If such events were rare, that backup could consist of
merely asking a reliable neighbour to check on him every hour or so.
If it was a frequent requirement, then I am sure that a backup system
could have been fitted that would not require manual intervention.

--
Cynic

Once the backup is in operation, there is no backup.