Smoke Alarms by Type and Battery Life in Rural Households

Background

Although the use of smoke alarms is widely recommended, little guidance is available on the types of alarms and batteries that function best. This study examined smoke alarm and battery function 12 months after installation in rural residential households.

Methods

An RCT, involving the installation of either a photoelectric or ionizing smoke alarm with either a lithium or carbon-zinc battery, was conducted in 643 rural Iowa households in July 2003. The functionality of each installed smoke alarm was tested 12 months later. Generalized estimating equations were used to model the effects of alarm type and battery type on alarm function and false alarms 12 months after installation.

Results

Of 643 study homes, 98.8% had at least one functioning alarm, and 81.5% had all alarms functioning 12 months after installation. No difference was observed in alarm function between photoelectric alarms and ionizing alarms 12 months after installation (OR=1.30, 95% CI=0.88, 1.92). However, photoelectric alarms had significantly lower odds of false alarms than ionizing alarms. Alarms with lithium batteries had 91% higher odds of functioning than those with carbon-zinc batteries. The main reasons for nonfunctioning included a missing battery (30.7%); a missing alarm (28%); and a disconnected battery (11.3%).

Conclusions

Although lithium batteries and photoelectric alarms are more expensive than their counterparts, the financial investment might be worthwhile in terms of overall performance.

Introduction

Fires and burns are the fifth most common cause of unintentional-injury deaths in the U.S.¹ and the third leading cause of fatal home injury.² In 2005, more than 3000 Americans lost their lives in residential fires.³ Most of these fire victims died from the inhalation of smoke and toxic gases and not as a result of burns; most fire deaths occur at night while the residents are asleep.4, 5 Smoke alarms minimize property damage, prevent injuries, and save lives by enabling residents to detect fires early and to escape safely from the building.6, 7, 8 Smoke alarms reduce by half the risk of dying in a fire7, 8 and by three fourths the risk of having a reportable fire.⁷

Smoke alarm types differ in how they detect smoke and in the power source they use to initiate an alarm. The two most commonly used smoke alarm types today are ionizing and photoelectric alarms. Ionizing alarms rely on a small energy source to create a constant electric current between two electrodes. When smoke or other particulates disrupt the current, electronic circuitry sets off the alarm. Photoelectric smoke alarms shine a small beam of light past a sensor. When particulates in the size range of smoke intervene, light is scattered into the sensor, activating the alarm. Photoelectric alarms react twice as quickly to smoldering fires, such as those caused by cigarettes igniting furniture, and are thought to reduce false alarms by being more sensitive to the chemical composition of smoke.7, 9, 10 However, photoelectric alarms cost about twice as much as ionizing alarms.¹¹

Battery-operated smoke alarms use a 9-volt battery. Most alarms include a carbon-zinc battery when purchased, and these have a short functional life compared to other battery types. Lithium batteries, in contrast, last up to ten times longer, but cost three to four times more.

No published studies as yet have examined the functionality of smoke alarm combined with battery type within rural residential households.12, 13, 14, 15, 16 Only two studies, one in inner-city London and one in King County, Washington, have used an RCT to examine smoke-alarm function. To date, only the London study12, 15 has published findings; these indicated that only half of the smoke alarms installed were still working 15 months later. This leads to questions about the long-term impact of smoke alarm installation programs. The London study also found that ionizing smoke alarms with lithium batteries were the most likely to remain functioning.12, 15 However, results from homes located in inner-city London may not generalize well to rural areas, where smoke alarm ownership is lower and fire deaths are 36% higher.17, 18, 19

Functioning smoke alarms may be more important in rural than urban settings because fires occur more frequently in rural homes.2, 17, 18 Rural homes are often a greater distance from neighbors as well as fire and emergency services, and occupants thus have less timely assistance in discovering a fire and escaping from the residence.2, 17, 18 Therefore, it is important to know which types of smoke alarms provide optimal outcomes in rural homes. The study's objective was to determine which smoke alarm type (photoelectric versus ionizing); battery type (lithium versus carbon-zinc); and alarm–battery combination were most likely to be functional 12 months after installation.