October, 2013
Inspection News and Views from the American Society of Home Inspectors

ASHI Smoke Alarm


October 2013 EDUCATIONhtml


ASHI Smoke Alarm White Paper


In 2012 the ASHI Board of Directors was furnished with evidence that deficiencies exist in the ionization smoke alarm technology installed in a vast majority of homes in the United States. After a thorough examination of the reports and information available, it became clear to the board there is substantial and credible evidence that ionization smoke alarms will not provide sufficient warning in certain types of fires that can be deadly to the occupants of a home. At the October 2012 ASHI Board of Directors meeting, a motion was passed that ASHI will advocate “the use of photoelectric smoke alarms in single and multi-family housing and discourage the use of ionization smoke alarms.”


Bill J. Loden

National President Elect

American Society of Home Inspectors



The American Society of Home Inspectors (ASHI) believes smoke alarms that use photoelectric sensing technology are superior to those that use ionization chamber sensing technology. ASHI recommends that homeowners replace existing ionization alarms with photoelectric alarms whenever possible.

Smoke alarms are intended to provide quick warning to allow people the chance to escape from a building before being overcome by smoke or heat from a fire. In too many cases, though, these safety devices fail to provide that warning, and people die as a result. Smoke alarms are widely available with two different sensing technologies: ionization and photoelectric. Ionization alarms have proven themselves to be particularly prone to nuisance alarms, which tend to cause people to disable them. Those that are not disabled fail to detect certain kinds of smoldering fires. Photoelectric alarms, in contrast, tend to be less susceptible to nuisance alarms and dramatically superior at detecting smoldering fires, particularly those that involve synthetic materials. Smoke inhalation from smoldering fires is a far more common cause of death in home fires than exposure to flaming-mode fires.

In the Smoke Characterization Project Technical Report, prepared for The Fire Protection Research Foundation by researchers with Underwriters Laboratories, the researchers found that ionization alarms were only slightly faster than photoelectric alarms in flaming-mode fires. But in smoldering fires, they were consistently slower than photoelectric alarms and, of much greater concern, ionization alarms failed to trigger at all in 91% of the tests of smoldering fires in synthetic materials such as mattress foam and nylon carpet. This might lead people to conclude that it would be best to have both kinds of alarms or, perhaps, an alarm with both kinds of sensors in it. However . . .

The Consumer Product Safety Commission’s Pilot Study of Nuisance Alarms Associated with Cooking found that ionization alarms produced far more nuisance alarms than photoelectric alarms, a trait that makes people tend to disable them. Surprisingly, combination alarms, which combine ionization and photoelectric sensors in the same device, produced more nuisance alarms than devices that had only one sensor of either kind – in some cases, the nuisance alarm rate for the combination units was twice as high as that of single-sensor units.

Texas A&M University’s Risk Analysis of Residential Fire Detector Performance was a 3-year study that tested the effectiveness of both types of alarms in two types of fire conditions: smoldering-ignition and flaming-ignition. This risk analysis found that, in smoldering-ignition fires, the probability of fatality due to failure of the alarm was 55.8% for ionization alarms vs. 4.06% for photoelectric alarms. In flaming- ignition fires, the probability of fatality due to failure of the alarm was 19.8% for ionization alarms vs. 4.06% for photoelectric alarms.

It’s easy to view these facts and studies in the abstract and allow political concerns to mitigate the discussion. The sobering reality, however, is that people die when smoke alarms fail. Therefore, the ASHI’s position on this topic is based solely on the facts that are available to us today and has not been mitigated by the opinions of other groups or organizations.


Given the current state of smoke alarm technology, ASHI advocates the use of photoelectric smoke alarms and discourages the use of ionization smoke alarms. ASHI recommends that homeowners replace existing ionization alarms with photoelectric alarms.


(Editor’s note: For more information about the differences between photoelectric and ionization smoke alarms, you can go to the ASHI website, click on the Reporter image, then click on Past Issues for the June 2013 Reporter with Skip Walker’s article “Silent Alarms; Deadly Differences.”)