Smoke Alarms (photoelectric)


All newly installed smoke alarms, including replacement smoke alarms, are now required to be photoelectric. Combination photoelectric and ionization smoke alarms are not permitted. Existing ionization smoke alarms are not required to be replaced unless installed in dwelling units within 20’ of a cooking appliance, or within close proximity (3’) of a bathroom containing a shower or tub. Ionization smoke alarms in these areas are required to be replaced with photoelectric smoke alarms to avoid nuisance alarms. Combination photoelectric and carbon monoxide alarms are permitted. NFPA 1:

Smoke alarms (detectors) provide important notification to people so they have time to escape from a fire. The time to escape from a fire is short and people need time to react and move to escape a fire, particularly when they have been sleeping, or are otherwise impaired.

How fast smoke alarms react to a fire has been the subject of research for over 40 years by organizations such as the National Institute of Standards and Technology (NIST), the National Fire Protection Association, Underwriters Laboratories, the U. S. Fire Administration and similar organizations. Findings from a 2004 study indicated that the burning characteristics of synthetic materials used in modern furniture and construction materials have reduced the margin of time available for escape, between when a smoke alarm first activates and the area becomes untenable for people, compared to studies done in 1975.

The lack of properly operating smoke alarms is a direct factor in fatal fires in Vermont. Smoke alarms were not operating in 86% of the fatal fires in Vermont during 1996-2005. Smoke alarms were not present in 38% of those fires, but smoke alarms were present in 32% of those fires but failed to operate soon enough to allow time for the people to escape. The placement of smoke alarms, the proper maintenance of smoke alarms and the type of smoke alarm are all factors why smoke alarms do not operate soon enough to allow time for people to escape.

There are two different types of smoke alarms in common use. Most smoke alarms used in dwelling units are ionization smoke alarms that react quickly to flaming fires from all types of fuels. However, smoldering fires are inherently different from flaming fires. According to NIST, “…ionization detectors have been shown to sometimes fail to alarm in a smoldering fire even when visibility in the room is significantly degraded by smoke.” Photoelectric smoke alarms react faster than ionization smoke alarms to smoldering fires.


Code Highlights