In 1992, the Building Regulations were amended requiring every new build to allow
for mains-wired, interconnected smoke alarms to be installed. With many alarms installed under this Regulation still in use and potentially approaching their twentieth year, it was necessary to research a recommendation as to when mains powered and battery operated smoke alarms should be replaced.
Current recommendations
The majority of research found on this subject emanates from the US. The US
National Fire Protection Association (NFPA) have issued NFPA Standard 72, National
Fire Alarm and Signalling Code (2010 edition), which states:
"Replace all smoke alarms, including those that use ten-year batteries and hard-wired
alarms, when they are ten years old or sooner if they don't respond properly when
tested."
US fire safety websites, along with those in the UK, Canada, New Zealand and
Australia, tend to recommend the replacement of domestic smoke alarms, whether
battery or mains-wired, when they:
- Fail to respond to tests
- Are ten years old (varying between date of installation and manufacture)
Why Replace Alarms?
Several reasons are provided to justify the replacement of smoke alarms after
ten years.
The Minnesota Department of Public Safety cite a nationwide study undertaken
by the Consumer Product Safety Commission (CPSC), which states that 97% of smoke
alarms should still be functioning after one year, if supplied with power. After
ten years it is 73%, whereas after 20 years, this figure stands at 54%. The study
also indicated that 60% of the failures were due to flat or removed batteries
or a disconnected power supply and the study offered possible reasons for this.
Ageing alarms may experience sensitivity drifting, which may, in turn, result
in an increased frequency of accidental activation and an increase in people removing
the power supply. It was thought that newer alarms with a 'hush' feature may contribute
to remedying this
An NFPA report cites a study undertaken by Canada's Ontario Housing Corporation
supporting the fact that 3% of smoke alarms will fail within one year. They also
say that after 30 years, nearly all the alarms will have failed. They conclude
that replacement after ten years, with roughly a 30% probability of failure, is
an appropriate balance between safety and cost
The South Australian Metropolitan Fire Service state that smoke alarm technology
has improved significantly since legislation was introduced (similar requirements
to the 1992 UK ones were introduced in Australia in 1995) and replacing old smoke
alarms is an ideal opportunity to upgrade smoke alarm systems. The Australian
Standard for smoke alarms (AS 3786) specifies an effective life of 10 years, suggesting
that after that time effectiveness may be compromised with accumulated dust, insects,
airborne contaminants and corrosion of electrical circuitry
In the early 1990s, the US Consumer Product Safety Commission undertook an extensive
study, called the National Smoke Detector Project, to examine smoke alarm ownership
and operability. Some failures were found in smoke alarms, but there were no
large or systematic problems identified with detector designs or manufacturing
practices that cast any doubt on their long term reliability. However, a variety
of component failures, corroded battery clips and deterioration and corrosion
of the horn element contacts were found in a few smoke alarms
Other reports from New Zealand and Canada looked at operability of battery smoke
alarms, but no further reports on the operability and longevity of mains-wired
smoke alarms could be found
Testing Smoke Alarms
It should be noted that the regular testing of smoke alarms should help identify
inoperability as testing a smoke alarm simulates smoke and does not simply test
the power supply. This would indicate smoke alarm maintenance messages remain
a priority. However, it was queried whether all smoke alarm test functions operate
in this way, or whether some simply do test power supply, be it battery or mains-wired
The general view from UK based smoke alarm manufacturers reflects the findings
elsewhere. With contaminants such as dust, insects, grease and nicotine, the
smoke alarm chamber is susceptible to becoming excessively sensitive or insensitive.
This may lead to either an increase in nuisance false alarms, or to eventually
becoming unable to detect smoke. One manufacturer reports that contamination is
extremely variable, but that field experience indicated that 10 years is a reasonable
compromise
Conclusion
Evidence of smoke alarm longevity appears to be scarce and inconclusive. As with
other electronic items, there will be failures in the units when they are produced
and failures during their lifetime due to individual component faults. Similarly,
as they get older more faults are likely to occur. Problems specific to smoke
detectors include increased sensitivity
In all the work identified so far, none has specifically concentrated on the
failure of smoke alarms when they age. Smoke alarms do fail but the rate at which
they do has not been accurately determined or related to their age.
Despite there not being much research, it does seem appropriate to replace smoke
alarms after ten years (in line with manufacturers advice), unless individual
alarm testing suggests earlier replacement.
Mains-wired interconnected alarms – Replacement kits
Safelincs has developed products designed to help facilitate the process of replacing the smoke detector heads for mains-wired interconnected smoke alarms