Imagine your car air bags deploying randomly when you hit a pothole or speed bump but failing to deploy over half the time in a collision. That is the stark reality with the smoke alarms that are most often found in North American homes. Like most, I had always assumed that a smoke alarm was a smoke alarm. What I now know is that there are two basic types of residential smoke alarms sold in the U.S.: ionization and photoelectric. In real-world fatal fires, these two types of alarms behave very differently. In this case – different is not good. Understanding the difference could very well save your life.
“A smoke detector that sounds approximately nineteen minutes after smoke reached its sensing chamber is like an airbag that does not deploy until nineteen minutes after a car accident.” - Judge David E. Schoenthaler, Mercer v. Pitway/BRK Brands (First Alert)
Over 90% of U.S. homes have ionization sensor smoke alarms installed. Around 5% of U.S. homes have photoelectric sensor alarms installed. Approximately 4% have no alarm of any kind installed. (footnote 1) Back in the 1960s, residential smoke alarms were almost unheard of and the fire death rate was about 7 to 8 fatalities per 1,000 U.S. home fires. Between the mid-70s and now, we have gone from about 10% of U.S. homes having smoke alarms to 96% of U.S. homes reporting having at least one smoke alarm. (footnote 2) Surprisingly, after installing smoke alarms in over 100 million U.S. homes over 30 years, the odds of dying in a fire remain about the same. Perhaps it’s just me, but that doesn’t make sense.
Between 1977 and 2009 the number of U.S. home fires and fire deaths have fallen by roughly 50%. However, the risk of dying when a fire occurs today is only slightly lower than in the 1970s. Over the period, the rate fluctuates considerably up and down between 6.5 and 10 deaths per 1,000 fires. This brings into question the value of installing hundreds of millions of ionization alarms.
Overall for the 1977-2011 period, the number of home fire deaths decreased from 5,865 in 1977 to 2,520 in 2011 for a decrease of 51%. The number of home fire incidents also declined steadily for an overall decrease of 49% for the same period. When the death rate per 1,000 home fire incidents is looked at (Figure 1), there is no steady decline, but rather the rate fluctuates considerably up and down. In fact, the death rate per 1,000 home fires was 8.1 in 1977 and 6.8 in 2011 for a decrease of 16%. These results suggest that even though the number of home fires and home fire deaths declined similarly during the period, the death rate did not, and when there is a home fire, the fire death rate risk has not changed much for the period.
The smoke alarm industry points out that all alarms and detectors must meet the standards developed by Underwriters Laboratories (UL). U.S. residential smoke detectors must meet the UL 217 standard. Alarms in Canada have a somewhat different UL-Canada (ULC) standard. For years the major smoke alarm manufacturers--UL, the National Fire Protection Association (NFPA), the Consumer Product Safety Commission (CPSC) and the National Institute for Standards and Testing (NIST)--maintained that either ionization or photoelectric alarms meeting the UL standard afforded adequate protection in most fires. Beginning circa 2006, their recommendations changed. After decades of saying that either alarm was adequate, they started to recommend that we have both types of alarms. The reason for this abrupt shift was never explained.
Most industry studies infer that all fires carry an equal risk of death. An analysis of the underlying data published by these same organizations does not support this position. In general, cooking/fast-flame fires account for a large percentage of fires and injuries but only about 15% of fire deaths. Bedroom and general living area fires are predominantly smoldering fires. This group accounts for only about 12% of fires but over half of all fire deaths and a third of injuries. (footnote 3)
Current UL alarm standards are essentially the same as those developed in the 1970s. Smoke alarm response requirements are defined in the UL 217 standard. The UL tests use a set of standard test scenarios and materials. One scenario is a “fast flame” fire, the other is for smoldering fires. A fast flame fire is the flaming/last stage of a smoldering fire or one based on accelerants, such as gasoline, cooking oils, grease, paper, etc. Fast-flame fires produce large quantities of sub-micron/small fast moving particles. A smoldering fire occurs in the early stages, before open flames develop. Smoldering fires produce slow moving particles. The smoke particles are much larger and tend to be fewer in number but more dense. The UL smoldering fire test standards were developed when most home furnishings were natural materials such as cotton, wool, etc. To simulate a smoldering fire such as one in upholstered furniture, UL smolders Ponderosa Pine sticks on a hot plate at slightly over 700 degrees with a fan blowing the smoke. Today virtually all furnishings and a large percentage of building materials are synthetic or engineered materials. The behavior and type of smoke produced by burning natural materials is radically different than those produced by burning synthetic ones. Yet the UL standards have not substantially changed for decades.
Under UL test conditions, ionization alarms consistently respond about 30 to 90 seconds faster to open or “fast-flame” fires than photoelectric smoke alarms. However, the vast majority of residential fire fatalities are due to smoke inhalation, not the actual flames. Nearly 2/3’s of fire fatalities occur at night while you sleep. Ionization alarms respond on average between 15 to 50 minutes slower in a smoldering fire than photoelectric alarms. Studies by UL,4 NIST, (footnote 5) Texas A&M (footnote 6) and others found ionization alarms may completely fail to activate in 20 to 25 percent of fires.
Let’s look at testing conducted on smoke alarms by one of our top universities. During 1991-1994, a research team at Texas A&M University, Department of Construction Science, conducted extensive testing on residential fire detection devices. The research project was titled “Full-Scale Research and Testing on Fire Detection Systems in a Residential Structure.” (footnote 7) The Texas A&M study concluded that, during smoldering fires, the probability of a fatality was 55.8% with ionization alarms but only 4.06% with photoelectric alarms. The study also concluded that, in fast-flame fires, the probability of a fatality was 19.8% with ionization alarms but only 3.99% with photoelectric alarms. This testing was based on a fault-tree analysis design developed by Bell Labs for the U.S. Air Force. The Texas A&M research clearly demonstrates that when all factors are taken into account, such as how often each alarm gets disabled due to nuisance alarm problems, to how they respond in actual testing across the full spectrum of fires, photoelectric alarms have a clear advantage.
In 2007, UL published the “Smoke Characterization Study”. This study tested both types of smoke alarms using current testing standards and materials; they also tested the alarms using UL test criteria integrating a variety of synthetic materials. The alarms were tested with burnt toast as well. The results are frightening. Ionization alarms failed the UL 217 test 20% of the time using required test materials. This is the test that the alarms must pass to even be offered for sale in the U.S. When tested using synthetic materials, ionization alarms Did Not Trigger (DNT) in 7 out of 8 synthetic test scenarios, for a 87.5% DNT rate. In the one test where the ionization alarm did trigger, it activated almost 43 minutes after the photoelectric alarm and at a level exceeding the maximum allowed under the UL 217 standard. Understand, this is UL running UL tests and showing that ionization alarms did not respond in 8 out of 8 smoldering test scenarios.
In the same UL tests, photoelectric alarms activated in 5 of 5 tests, or 100% of the time using the standard UL 217 test materials. Photoelectric alarms activated properly in 8 of 8 synthetic material tests, a 100% activation rate. The ionization alarm outperformed the photoelectric in only one case, the burnt toast test. There the ionization alarms responded 22% faster.
It should be noted that there were three test scenarios where neither alarm activated. The researchers determined that the sample size used was too small to generate sufficient smoke. (footnote 8) Those materials were retested using larger samples, and the results included in the above eight test scenarios.
The issue with ionization alarms is far more than just the slow response to deadly smoldering fires. Ionization alarms are notorious for nuisance tripping. They frequently go off when you cook, burn toast, shower, etc. When alarms nuisance trip, people become frustrated and intentionally disable them. This leaves their families completely unprotected. Several CPSC and NFPA studies report that 97% of all nuisance alarm activations are from ionization alarms.9 An Alaskan Public Housing Study shows that about 19% of ionization alarms were disabled within six months of installation; 10 other studies indicate that the percentage may be higher.
“Considering photoelectric smoke alarms are deter-mined by industry experts to be significantly less prone to nuisance alarm and potential disabling of the batteries by consumers, we support and encourage fire service administration and lawmakers that are moving toward the use of photoelectric smoke sensing technology.” - BRK/First Alert Letter to Vermont fire departments, July 17, 2008
Remember, about 96% of US homes have at least one smoke alarm. Nearly two-thirds of all residential fire deaths occur in homes that are unprotected. Roughly 50% of homeowners with nonfunctional alarms cite nuisance tripping as the reason for disabling their alarms. To complete the picture, many of the remaining 1/3 of residential fire deaths occur in homes where an alarm sounds, but it sounds too late for the occupants to escape. Over the years a number of government, university and manufacturer research studies, many going back to the mid-1970s, clearly show that ionization alarms are slow to react in deadly smoldering fires and account for the vast majority of nuisance trips.
It has taken decades, but there is finally a growing public awareness of this issue. On October 3, 2012, the NBC Today Show and NBC Nightly News aired a “Rossen Report” investigative segment on this issue. On July 7, 2012 with a follow-up report on August 1, 2012, Huntsville, Alabama TV station WHNT aired “A Taking Action” investigative report featuring ASHI President-Elect Bill Loden. On November 16, 2012, San Francisco CBS 5 "ConsumerWatch" aired a segment with Albany, California retired Fire Chief Marc McGinn and me demonstrating the poor performance of ionization alarms.
The International Association of Firefighters (IAFF) is the largest firefighters union in the U.S. and Canada, with nearly 300,000 members. During the IAFF 2008 conference, they adopted an official position recommending that only photoelectric smoke alarms be installed. The IAFF position also commits the organization to working for changes in the law and model codes to require photoelectric technology alarms. Further, the IAFF position specifically states that combination type alarms are not acceptable. In July, 2010, Albany, California became the first city in that state to require photoelectric smoke alarms in new construction and remodels. In California, the cities of Palo Alto, Orange and the Sebastopol have enacted ordinances requiring photoelectric technology alarms. Shaker Heights, Chagrin Falls and several other cities in Ohio have enacted similar ordinances.
In 2011, the California Real Estate Inspection Association (CREIA) became the first home inspection organization to take a stand when it adopted a position mirroring the IAFF position. At the January 2013 Board of Directors meeting, ASHI became the first national home inspection organization in the world to take a stand when it adopted a pro-photoelectric alarm position. At this time, Vermont, Massachusetts, Maine and Iowa have laws that require photoelectric technology alarms in residential construction. Similar action is under consideration in several states. Cincinnati, Ohio recently became the largest U.S. city to enact a photoelectric ordinance. The ordinance covers rental housing. Six smaller cities in Ohio have photoelectric ordinances. New York City is currently considering a photoelectric ordinance. The Northern Territory in Australia recently adopted a photoelectric technology law.
The New York Senate and Assembly are currently considering a photoelectric smoke alarm tax credit referred to as Averyana’s Law. (footnote 11) As part of the justification, the law states: “On March 11, 2012, two year old Averyana Dale tragically lost her life due to smoke inhalation in a fire in Auburn, NY. “ It was later determined that the fire was a smoldering fire, which produces a significant amount of smoke but very little actual flame. Averyana Dale and her godmother most likely lost their lives because the ionization smoke detector that was present in the home did not alert to the fire until it was too late. If a photoelectric detector had been in the home, it is considerably more likely they would have been alerted to the smoke significantly sooner and would have made it out safely.
“Nationally, the percentage of people dying when the smoke detector works, but works too late, is approximately 40 percent.” - Jay Fleming, Boston Deputy Fire Chief, CBS Boston Interview, 2007
WHICH TYPE OF TECHNOLOGY DO I HAVE? It is not always possible to know. In general, if the label says anything about radioactive material, Americium-241 or the model number has an “I,”—then it is almost certainly an ionization alarm. If you have any doubt, there is over a 90% chance that the alarm you have is an ionization unit. Photoelectric models often have the word “photoelectric” or the capital letter P printed or embossed on them. To be safe, simply replace any unknown units with photoelectric-only alarms. Any smoke alarm that is 10 years old or older should be replaced regardless of type.
WHAT ABOUT COMBINATION ALARMS? There are combination photoelectric/ionization smoke alarms available. At first blush, these seem like a perfect solution. For this reason, many mistakenly recommend them. There is no industry standard for setting the individual sensor sensitivity in combination alarms. As long as the alarm responds within the UL 217 requirements, the manufacturers are free to adjust each sensors sensitivity levels. These units have the same issues as ionization-only alarms. In some instances – they may be worse. A CPSC study shows that they may be even more prone to nuisance tripping than ionization-only alarms when in very close proximity to cooking sources. (footnote 12)
Photoelectric [P] on smoke detector.
Ionization smoke detector label.
The definition of a combination alarm is found in NFPA 72. NFPA 72: A.126.96.36.199 states: “These detectors do not utilize a mathematical evaluation principle of signal processing more than a simple “OR” function. Normally, these detectors provide a single response resulting from either sensing method, each of which operates independent and distinct of the other. These detectors can provide a separate and distinct response resulting from either sensing method, each of which is processed independent from the other.”
Newer combination alarms use what is called “OR” logic. With “OR” logic, either sensor can sound the alarm. The photoelectric sensor picks up the smoldering fires, so the ionization sensor does not become a factor. However, the ionization sensor is still susceptible to nuisance tripping. The manufacturers do not want the customer to disable the alarm. To combat nuisance tripping, manufacturers often reduce (desensitize) the smoke sensitivity/response of the ionization portion of a combination alarm. The net effect is that “OR” alarms perform similarly to photoelectric-only alarms in smoldering fires. (footnote 13)
Older combination alarms may use either “AND” or “OR” logic. In “AND” units, BOTH sensors must trigger to sound the alarm. In these units, the photoelectric portion will pick up the smoldering fires first but will not sound until the ionization sensor triggers. Since a smoldering fire poses the greatest danger, this is a problem. The family is often asleep while the alarm waits quietly for the ionization sensor to finally trigger. Conversely, while this unit will be less susceptible to nuisance tripping because the photoelectric sensor must also respond to nuisance sources such as burnt toast, you risk losing your life if the ionization doesn’t respond in a dangerous smoldering-fire situation.
NIST is on record stating, “Since an individual sensor can be set to meet all current sensitivity standards, it is not obvious what overall benefit is achieved from a dual alarm.” (footnote 14) In the same NIST report, they indicate that when the combination alarm responded faster to smoldering fires, it is because the photoelectric sensor responded first. When the ionization sensor in a combination alarm nuisance trips and the battery gets removed, there is no protection. That scenario accounts for 1/3 of all U.S. fire deaths.
The International Association of Fire Fighters (IAFF), CREIA and ASHI specifically recommend against installing combination alarms. In the simplest terms, if you take a device that works and pair it with a device that has serious shortcomings, how can that possibly improve performance?
There are also combination photoelectric/carbon monoxide (CO) alarms. Smoke and CO alarms experience an estimated 3% random failure rate per year. Much like a light bulb, they simply burn out. With combination alarms, if you lose one – you lose both. These are life-safety devices. A single point of failure in a life-safety system is bad. For safety reasons, all smoke alarms should be replaced every 10 years or less. Depending on the manufacturer, CO alarms should be replaced every 5 to 7 years. With combination CO/smoke alarms, you must replace the smoke alarm portion more often than really needed based on the CO replacement period. Separate units simply make more sense.
In conclusion, we know that no one alarm can save everyone in every possible circumstance, and we know there are many promising technologies being developed. That said, Deputy Boston Fire Chief Jay Fleming estimates that “about 1,000 people die needlessly in residential fires, with thousands more seriously injured each year.” With everything we know, the facts tell us that photoelectric alarms provide superior protection across the broad spectrum of real-world fatal fires. Photoelectric alarms are available today, and they cost only a few dollars more than ionization alarms. Do not allow your family, friends, neighbors and clients to become one of these statistics. This year, don’t just replace your smoke alarm batteries – replace your alarms with photoelectric alarms and recommend that everyone you know do the same!
Skip Walker, ACI, is a CREIA Master Inspector, ICC Certified Combination Residential Building Inspector and a FIRE Certified Fireplace Inspector. He has presented to the National Association of Realtors®, the California Association of Realtors® on smoke alarm performance and CO poisoning issues. He has presented at ASHI InspectionWorld 2013, ASHI GLC , ASHI Ohio, ASHI Western Washington and a number of CREIA conferences /meetings on smoke alarm performance issues. Walker has served in numerous capacities for CREIA and ASHI and written extensively on smoke alarm and CO issues. Skip’s home has ONLY photoelectric alarms installed. You may reach Skip at (650) 873-4224 or by email at HomeInspection@sanbrunocable.com.
Thanks to the following: Dean Dennis, Fire Chief (Retired) Marc McGinn, city of Albany, California, Dr. Larry Grosse, PhD, University of Colorado (and former researcher at Texas A&M), Adrian Butler, Chairman World Fire Safety Foundation, Boston Deputy Chief Jay Fleming and Dr. Don Russell, Texas A&M. This article would not have been possible without the support and guidance of these amazing individuals.
Patty and Andrea Dennis
Dean and Andrea Dennis
SIDE BAR: Julie Turnbull & Andrea Dennis Julie Turnbull was in her junior year at Miami University in Ohio. Julie died along with Kate Welling and Steve Smith in an off-campus dorm fire on April 10, 2005. She was 20 years old at the time of her death. The fire is believed to have been started by a cigarette in a couch and appears to have smoldered for one to two hours before erupting into flames. As is usually the case, it was the smoke that killed. One of the victims was found on the first floor near the door, apparently trying to escape. From what was pieced together from neighbors and those who escaped, thick smoke had already engulfed the house before a single smoke alarm even sounded. At this point, it is likely that Julie and the others were already dead. The house had 17 smoke alarms installed. Some were disabled by the kids who were apparently annoyed by the alarms’ constant nuisance tripping when they cooked. All of the alarms were ionization alarms. Most never sounded during the fire.
Andrea Dennis was a month away from graduation at Ohio State. She and four others died on Palm Sunday, April 13, 2003. The circumstances were all too similar to Julie’s death. Andrea’s father, Dean, reached out to Julie’s father, Doug, at Julie’s funeral service. In their search for answers, the issue of ionization alarms became very personal. They went on to found Fathers for Fire Safety as a way to educate the public and fire service about this critical issue. This group works closely with the World Fire Safety Foundation, an organization instrumental in educating the fire service community and general public about this critical issue.
Dean Dennis states, “I believe the photo would have gone off first, giving my daughter (Andrea) at least a chance…. It is my belief and the belief of Doug Turnbull, Julie’s father, that Julie would be alive today if the smoke alarms had been photoelectric alarms.”
About two years after Andrea’s death, the house where she had died was rebuilt and occupied. A new group of Ohio State students occupied the new dwelling. A walk-through of the property confirmed that smoke alarms had been installed when they rebuilt. There were wires dangling from many of the ceiling mounted smoke alarm boxes. The students had gotten tired of the constant nuisance tripping and had removed them. The ones left all proved to be ionization alarms.
If we do not learn from the past, we are condemned to repeat it. And the consequences will be deadly.
9 NFPA, Home Smoke Alarms – The Data as a Context for Decision, 2008 & False Alarms and Unwanted Activations – US Experience with Smoke Alarms, 2004, Ahrens. Also, National Smoke Detector Project, 1994
10 Western Journal of Medicine, 2000 August; 173(2): pages 89–92, Fazzini, Perkins, Grossman
11 New York State, Bill S3299A-2013, Averyana’s Law, http://open.nysenate.gov/legislation/bill/S3299A-2013
12 CPSC, Smoke Alarms – Pilot Study of Nuisance Alarms Associated with Cooking, March 2010
13 NIST, Performance of Dual Photoelectric/Ionization Smoke Alarms in Full-Scale Fire Tests, 2009
14 Thomas Cleary, Presented at the Fire Protection Research Foundation’s Suppression and Detection Research & Applications Symposium (SUPDET 2009), February 24, 27, 2009