3

good. But, the test also will show that many ionization detectors will not
activate until the smoke obscuration reaches 10-20% (29 – 52% Obs/m) and
sometimes 25% (61% Obs/m). Therefore, because of the present state of
the art in detecting smoke, the Subcommittee on Smoke Detectors can take
no other course but to recommend the installation of photoelectric
detectors."
(Note: Italics added by editor)

• R. Riley, K., and Rogers, S. in A Study of the Operation and Effectiveness of Fire
Detectors Installed in the Bedrooms and Corridors of Residential Institutions, Fire
Research Station, Fire Research Current Paper 26/78, Borehamwood, England,
April 1978, concluded,
"Ionization chamber type detectors, in the room of origin and the corridor, did
not, in the smoldering fire tests, provide adequate warning that the escape
route was impassable or that conditions in the room were potentially
hazardous to life".

• The case of Jeanna Rodgers reported by consumer.org.nz illustrates the concern
with the ability of ionization alarms to detect visibly dense smoke. On August 2 2006
a clothes dryer failed filling the house with smoke. There were three ionization
alarms installed within the house and all failed to alarm. Whilst the report does not
state that smoke was observed to have reached the ionization alarms it would be
reasonable to assume with three installed it would have been the case. The alarm
was raised by Jeanna's five year old son, Samuel, who sleeping on the top bunk was
awoken when he started to cough from the smoke layer which had now descended
to where Samuel was sleeping. When the three ionization smoke alarms were tested
in situ by the attending fire service all three operated correctly.

• In 1988 UL, as a result of high level of nuisance alarms from ionization smoke
alarms, decreased the sensitivity requirements from 7%obs/ft (21.2% Obs/m) to
10%Obs/ft (29.2% Obs/m) as a means of mitigating the problem. However as
ionization detectors respond to fast flaming fires this potentially meant the detection
of the fire at a more advanced flaming stage than previously. This may explain the
significant changes in the number of fire fatalities that occur in fires where the smoke
detector has operated. Detection at a later stage must impact on the ASET. The
table below shows a disproportionate increase in the number of post alarm fatalities
compared to the home coverage and number of fires.


% OF FATAL FIRES WITH % OF HOMES WITH % OF FIRES WITH
WORKING DETECTORS DETECTORS WORKING DETECTORS
1988 9% 81% 38%
1990 19% 86% 42%
1994 19% 93% 49%
1996 21% 93% 52%
1998 29% 94% 55%
2001 39% 95% 55%
Source: Joseph M. Flemming, Deputy Chief, Boston Fire Department, Photoelectric and
Ionization Detectors; A Review of the Literature Revisited.


• A search of published studies and papers has produced no document that concluded
that photoelectric detectors, with current "open" design, were inadequate for flaming
or smouldering. This would appear to constitute "compelling evidence" that ionization
detectors are not suitable for residential occupancies as stand alone devices, since a
reasonable alternative is available as a Deemed to Satisfy solution. While it may be
true that no single study is enough proof of this problem the totality of all of the
studies provided considerable evidence that this problem is real.
Source: Joseph M. Flemming, Deputy Chief, Boston Fire Department, Photoelectric
and Ionization Detectors; A Review of the Literature Revisited
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