Australian Building Codes Board

PRELIMINARY IMPACT ASSESSMENT FOR BCA VOLUME 1 & 2
REVISION OF PRODUCT STANDARD
AS 3786 —1993 Smoke alarms


Version 2: 1 February 2007


Nature and Extent of the Problem:
Standards Australia on behalf of committee FP-002 Fire Detection, Warning, Control and
Intercom Systems, proposes to revise AS 3786 because of an identified anomaly in the current
edition of the Standard. The current edition allows two pass criteria for the same product (i.e.
smoke alarms), resulting in different performance outcomes. Table 3.1 of AS 3786 shows a light
obscuration pass criteria for photoelectric type and a MIC-X value for ionization type. Australia is
the only country that uses two different pass criteria, all other regional and international
Standards use an acceptance criteria based on light obscuration.

Standards Australia technical committee FP-002 identified that the design fire within residential
accommodation is statistically a smouldering fire. This, coupled with maintaining tenability within
paths of travel to an exit, is a function of the level of light obscuration and toxic species.

CSIRO have reported to FP-002 that the different criteria result in significant differences in the
performance of smoke alarms. Photoelectric smoke alarms, when tested in accordance with the
requirements of AS 3786—1993, typically respond between 8% and 16% obscuration per metre
(Obs/m) whilst ionization smoke alarms typically respond between 40% and 60% light Obs/m
(0.25 to 0.6 MICX), with the majority of ionization smoke alarms operating at the least sensitive
end of this range (See Appendix A, CSIRO test graph and explanation).

Under the current Standard, ionization smoke alarms are permitted to have a lesser response to
obscuration, which results in a significant negative impact on the Available Safe Evacuation
Time (ASET).

Australian and international research demonstrates that the highest number of fatalities in
residential fires occurs between the hours of 8.00 p.m. and 8.00 a.m. when occupants are
typically sleeping and these fires typically begin with a smouldering phase. Of principle concern
is the impact of resultant smoke obscuration and toxic species on the occupants' ability to
escape.

The Standards Committee FP-002 cites the following three points in support of the revision of
AS 3786.

ONE
Australian and international research that indicates ionization smoke alarms have
performance limitations in adequately detecting smouldering fires in time to provide
adequate ASET before untenable conditions exist.

• The Australasian Fire Authorities Council report titled Accidental Fire Fatalities in
Residential Structures; Who's at risk? (Oct 2005), gives the three major causes of
fatal fires in Australia as, heater/open fire/lamp (27%), smoking materials/equipment
(25%), and electrical fault (23%). These fires typically have an extended smouldering
phase.






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