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ARW

On 25/11/2018 18:11, wrote:
On Sunday, 25 November 2018 13:14:40 UTC, Peter Parry wrote:
On Sat, 24 Nov 2018 15:42:20 -0800 (PST), tabbypurr wrote:
On Saturday, 24 November 2018 17:49:47 UTC, Peter Parry wrote:
On Fri, 23 Nov 2018 08:07:18 +0000 (GMT), "Dave Liquorice"
wrote:
On Thu, 22 Nov 2018 20:50:03 +0000, Max Demian wrote:

However the most disturbing one is a flat that a tenant moved into
4
weeks ago. The mains had been disconnected from the smoke, taped
up and
shoved into the ceiling as well as the battery having been
removed.
Almost certainly like that when she moved in 4 weeks ago.

Implying that the Land Lord didn't check the detector as part of any
"pre delivery inspection".

If they are linked burning toast in one flat will set them all off.

Which depending on the buildings construction (and modifications)
might be a good thing... However such a system has to be fairly
immune to false alarms from burning toast,

An alarm from burning toast is not a false alarm but the detector
doing its job and alerting the occupants that it has detected the
products of combustion (not necessarily smoke).

it's a false alarm because there is no fire, no reason for the occupants to evacuate.

or the smokes will get
disabled. If the kitchen opens into the hallway the chances are it
won't be immune to false alarms. A hallway detector needs to be a
smoke based one not temperature.

Therein lies problem, Mrs Smith is a bit forgetfully and often singes
the bacon or overcooks the toast. Mr Jones the student doesn't
understand that letting the baked beans sit on the hob for 60 mins
will write off another saucepan and set off the alarms. Mr Williams
who works nights is seriously ****ed off by being constantly woken by
these events so whacks the detector until it stops making a noise. Mr
Abdul smokes a Hookah which regularly sets off the alarm because some
well meaning idiot put a detector in the lounge.etc. No one has yet
discovered a reliable "Hey this really is a fire you need to do
something!" alarm.

Yes they have. They're called heat alarms.

Neither fixed point trigger nor rate of rise heat alarms are adequate
for protecting occupants from common causes of fire. They belong only
in kitchens, utility rooms and garages where fires are likely to
start quickly and other detectors cannot be used. Rate of rise
detectors can also suffer nuisance alarms if for example they are
positioned above oven doors where the out rush of hot air when the
oven door is opened can cause them to trigger.

The reason we also use ionisation & optical detectors is because they detect real fires
much earlier in the process, giving much improved odds of survival. The downside is false alarms.

Neither optical nor ionisation detectors detect fires. Both detect
products of combustion. Quite often victims of fires are found away
from the source of the fire. Very few people burn to death, the fumes
(Carbon Monoxide in particular) kill them first and the influence of
heat is of minor importance.

Perhaps the way forward might be a building-wide heat alarm system with local ionisation alarms that only warn locally. Maybe.

Heat alarms trigger at about 60 deg C (fixed point) or for rate of
rise detectors by about 8 deg C per minute rise. Neither are useful
for life protection in common areas because by the time the fire is
sufficiently developed to trigger temperature alarms it will already
be producing lethal levels of fumes. Hence their only use is in small
confined areas such as kitchens where fires are likely to start and
either ionisation or optical alarms will routinely produce
unacceptable numbers of nuisance alarms or become compromised over
time by atmospheric contamination.

The other somewhat obvious thing is to position the alarms correctly, something many simply don't do.
Advice to do that even got deleted from the wiki. Even an ionisation alarm doesn't false alarm in a kitchen if positioned well.

Positioning is important but unless a kitchen is only used to warm
food and nothing will ever get burned an ionisation alarm is wholly
unsuitable in a kitchen no matter where it is installed. In a normal
two story construction the critical sensor is the one placed on the
ceiling at the top of the stairs. That will trigger first in about
80-90% of cases no matter where the fire starts. Even quite badly
placed alarms will work in most cases, just not as quickly as they
could.

Unfortunately fire protection by combustion detectors is one of the
fields where too many people believe that more = better and fail to
understand that if there are too many (and too many is a small number)
nuisance alarms then occupants will both ignore and later disable the
alarms. "I've put lots of sensors in so its much safer" often really
means "I've put lots of sensors in so its much less safe but I've
created a really good illusion of safety".

You and most people are wrong on one point. Ionisation alarms can cover kitchens with no significant false alarms IF positioned correctly. Obviously 'correctly' there means something different than for other alarm types or in other locations.

That goes against the advice from every manufacturer.

--
Adam