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How Many Lives Do Smoke Alarms Really Save?

Last year, we put out a podcast called “Death By Fire? Probably Not.” It was about the remarkable decline in fatal fires in the U.S. over the past century, and explored some of the contributing factors.
Joseph M. Fleming, a deputy fire chief with the Boston Fire Department, has now written in with a guest post that challenges what we think we know about smoke alarms. Fleming has more than 30 years of experience in the fire industry (in both firefighting and management), and suggests that people think a little harder about smoke alarms.

Do Smoke Alarms Really Save Lives?

By Joseph M. Fleming

As a deputy chief on a major municipal fire department, I have preached for years about the life-saving benefits of working smoke alarms.  I also trust the lives of my family to the eight smoke alarms installed in my house.  However, some of the available data regarding smoke alarms raise disturbing questions about the actual effectiveness of smoke alarms at reducing fire deaths in the U.S.

In the illustrated edition of SuperFreakonomics, the following chart appears. It shows a continuous downward trend in fire deaths for the last 90 years and particularly for the last 50 years. 

Now I would like to provide information on how smoke alarm usage has increased over time.  Most of these smoke alarms were single-station, battery-powered ionization alarms.

Keeping this chart in mind, consider the following statement from the U.S. National Institute of Standards and Technology:

According to estimates by the National Fire Protection Association and the U.S. Fire Administration, U.S. home usage of smoke alarms rose from less than 10% in 1975 to at least 95% in 2000, while the number of home fire deaths was cut nearly in half. Thus the home smoke alarm is credited as the greatest success story in fire safety in the last part of the 20th  century, because it alone represented a highly effective fire safety technology with leverage on most of the fire death problem that went from only token usage to nearly universal usage in a remarkably short time.

If the ionization smoke alarm was responsible for most of the decrease in fire deaths in the last part of the 20th century, shouldn’t the rate of decrease have been greatest over the time period that smoke alarm usage increased the fastest?   Yet over the time period of 1977–1987, when the use of smoke alarms skyrocketed, the trend line remained relatively constant.  The death rate was trending down before smoke alarms and continued to trend down after they saturated the market.  It does not appear that ionization smoke alarms affected the trend line. NIST inexplicably ignores the trends in better building codes, reduction in smoking, better firefighting equipment, and better emergency medical care as likely reasons for the reduction in fire deaths.

I would like to analyze another statistic often cited to support the effectiveness of smoke alarms: “The death rate in fires with working smoke alarms (0.52 per 100 fires) was less than half (56% lower) than the risk of death from fires that did not have working smoke alarms (1.18 deaths per 100 fires), either because no smoke alarm was present or an alarm was present but did not operate.”

However, these numbers are skewed by including “confined fires” — i.e., fires that are contained to the object of origin.  Over this time period (2005–2009), no one died in this type of fire if the fire was big enough to operate the alarm.  If, using the same report, we only analyze “non-confined” fires, we get the following death rate per 100 fires for homes.

This is only a 29 percent reduction in death rate (1.15 versus 1.64). Given that some of the reduction is probably due to socioeconomic factors that accompany smoke alarm ownership, the reduction in risk attributable to the alarm is less than this percentage.  The numbers for apartments are even more troubling.

In apartments, smoke alarms only reduce the risk of dying in a fire by 18 percent (1.17 versus 1.42). 

It is highly probable that the main reason for the lack of effectiveness of operating smoke alarms is that most smoke alarms utilize ionization technology (the less-expensive kind of alarm). This technology has been shown to operate only after dangerous conditions have developed during smoldering fires, and these types of fires are extremely common during the times when occupants are sleeping and relying on the alarm to alert them.  It is one of the reasons that some states — Massachusetts and Vermont, for example — as well as the International Association of Firefighters recommend the use of photoelectric smoke alarms. (The eight smoke alarms in my house are photoelectric alarms.)  Another reason is that photoelectric alarms are far less likely to sound nuisance alarms and, as a consequence, are less likely to be disabled.

More information on this topic can be obtained at the following links:

Smoke Detector Technology and the Investigation of Fatal Fires

Smoke Alarm Information from the International Association of Firefighters