Smoke alarms – what is the right kind?

By Ed Comeau, Publisher, Campus Firewatch

Copyright 2008©

The following is a special reprint from the February issue of Campus Firewatch™.

There is no question that smoke alarms have had a significant role in reducing the loss of life across the nation. According to some reports, 96% of the homes in the country have a smoke alarm installed in it. However, not all of these are working, not all are properly located and there may not be enough of them to provide coverage. These are issues that are well known to the fire service and that they have grappled with for many years.

Since January 2000, Campus Firewatch has identified 126 fire deaths with 83% of them occurring in off-campus housing. One of the common factors identified in these fires has been disabled or missing smoke alarms, similar to housing in society at large. Just getting students to have a working smoke alarm in the first place is often the biggest challenge. However, a new issue has come to the forefront – what type of smoke alarm is the most effective one in saving lives?

There are two types of smoke alarms that are in widespread use that use different sensing technology. Photoelectric relies on the light-scattering principle and ionization technology ionizes the smoke particles. Both provide warning, but the type of smoke condition that they react to is different. Ionization is the more common technology being used by consumers and sold in stores.

Across the nation, television stations are conducting similar demonstration burns where a fire is lit inside of a fire department burn building, with several smoke detectors located on the ceiling. The fire, usually a smoldering one, generates smoke and the news crew waits to see which smoke alarm reacts first and, generally, it is the photoelectric smoke alarm. The ionization then activates, but sometimes after a significant delay. These demonstrations have raised questions that the fire service is attempting to address. (In researching material for this article, a search was done on Google News for media stories on photoelectric and ionization smoke alarms. Within the past 30 days there were 20 news stories across the nation.)

In addition, some jurisdictions are looking at legislating what type of smoke alarm should be used in new construction. Boston recently held a hearing on this topic, as did the Massachusetts State Fire Marshal and the Vermont state senate. According to media reports, Tennessee is also looking at filing legislation.

Ionization smoke alarms are the predominant smoke alarm being used in homes across the country. However, in industrial or commercial occupancies which are equipped with fire alarm systems and use smoke detectors (as opposed to smoke alarms), photoelectric technology is more commonplace. Marriott Hotels, well known for its aggressive approach to fire safety, started switching all of their rooms over in 2003 to photoelectric technology because of its superior performance in detecting smoldering fires. At a recent hearing in Massachusetts, one fire alarm manufacturer reported that they almost universally use photoelectric technology on the systems they install.

In 2004, the National Institute of Standards and Technology conducted a series of tests to determine under what conditions each smoke alarm would react and the time for it to alarm. These tests were conducted in a two-story home and in a manufactured home in order to measure the impact in different geometries. In addition, there were different placement scenarios tested where smoke alarms were located in differing proximities to the fire. The two types of technology were tested, as were dual-sensor smoke alarms that contain both types of technology in a single unit.

These tests were funded by U.S. Consumer Product Safety Commission, Centers for Disease Control and Prevention, U.S. Fire Administration, the U.S. Department of Housing and Urban Development, Healthy Homes Initiative and Underwriters Laboratories. The National Fire Protection Association and National Research Council Canada provided in-kind contributions to the project.

Two different types of fires were simulated, one an open-flaming fire and another a smoldering fire. The reason for the different types of fires is that each one generates different types of particles and the air movement on each type of fire is different. The five types of scenarios were selected based on their frequency in both occurrence and the number of fatalities attributable to the scenario. (Note that this is data from 1992 to 1996 that was used in developing these tables and scenarios.)

Fire scenarios ranked by number of deaths (leading five scenarios)

Based on the scenarios identified for both frequency of occurrence and number of deaths, the following five test scenarios were developed.

• Smoldering upholstered furniture in the living room,

• Flaming upholstered furniture in the living room,

• Smoldering mattress in the bedroom,

• Flaming mattress in the bedroom, and

• Cooking materials in the kitchen.

The results were reported extensively in the report, and the following is just one portion of Table 23 which is the average time to alarm (in seconds) in a manufactured home. The common factor in a number of the trials was that the photoelectric smoke alarm would react faster to smoldering fires while the ionization would react faster to open-flaming fires.

Initially, when looking at the tables that summarized the performance of the smoke alarms in a wide variety of scenarios (Tables 23 and 24, pages 234 and 235 and Tables 27 and 28, pages 242 and 243), one issue leapt out. The performance of dual-sensor smoke alarms that incorporate both photoelectric and ionization detection in a single unit did not appear to mirror the performance of the stand-alone units.

The performance of a dual-sensor unit as reported was behind either stand-alone smoke alarm in a large number of the cases. In some, it took the dual unit 22 times longer to activate than a standalone (64 seconds vs. 3602). While that is one of the extreme cases, in almost all of the scenarios the performance of the dual sensor was significantly behind a stand-alone smoke alarm. In some of the results, the dual-sensor did not activate at all prior to the conclusion of the test.

Campus Firewatch contact NIST regarding these results which were reported in 2004 (a revised report was issued in December 2007 and still included the same information about the dual-sensor smoke alarms). Upon investigation, the NIST spokesperson reported that the discrepancy was because the dual-sensor smoke alarms listed in the results alongside the photoelectric and ionization smoke alarms were, in fact, placed in a different location leading to differing results. The NIST spokesperson said that they are going to modify the report and remove the dual sensor results from the tables to avoid future confusion. NIST did not respond to questions regarding the actual placement of the dual-sensor alarms in relation to the fire and the stand-alone detectors (i.e., were they closer or further away) and why they were set up and reported in this manner.

NIST did provide Campus Firewatch with data from the appendix of the report on dual-sensor smoke alarms that were co-located with the stand-alone smoke alarms.

The results of these tests would seem to indicate that the performance of a dual-sensor smoke alarm is comparable to those of the stand-alone alarms. However, given that these results were not initially reported in the body of the report and the confusion that has arisen, this issue needs more scrutiny before reaching a conclusion.

NIST Spokesperson John Blair provided the following statement to Campus Firewatch:

“In certain places in the report tables show response times or available safe egress times for the three different smoke alarm systems --ionization, photoelectric and dual sensor (ionization and photoelectric) side-by-side.  Although the times are valid for the individual respective alarms, the alarms were not necessarily at the same location, making a comparison of the three types of alarms inappropriate.  To avoid confusion, the researchers are revising the tables to show only co-located alarms systems.  At every place a change is made, the change will be noted with a clarification.  All material on individual smoke alarm system responses will continue to be in the Appendix for those who wish to construct specific comparisons.  The chart of the response times of three co-located types of systems, which Thomas Cleary (NIST researcher) provided for you, for instance, came from individual alarm responses in the Appendix.”

This leads back to the initial issue of what is the most appropriate type of smoke alarm to be using in off-campus housing?

Tenability Factors

The goal of any smoke alarm is to sound the alarm before conditions become untenable and provide the occupants with the maximum amount of time possible to escape. Part of the NIST tests were also to measure heat, gases and smoke obscurity and correlate tenability conditions against smoke alarm activation.

A key part of the tenability determination requires looking at how long it will take people to evacuate a building, which is a complex matter. It involves evaluating reaction time to alarms, pre-movement activities, movement time and other factors for a wide variety of populations and building types. According to the report, pre-movement activity could include notifying others in the building, getting dressed, notifying the fire department, investigating the fire, fighting the fire, and leaving the building.

Another of the common factors identified by Campus Firewatch in a number of the fatal fires since January 2000 is the involvement of alcohol which can either suppress an individual’s judgment or impact their response or ability to react in a timely or appropriate manner before untenable conditions are reached.

Campus Firewatch worked closely with USA TODAY in helping the newspaper prepare a major story on the impact of alcohol on campus-related fire deaths. Research conducted by USA TODAY of 43 fires that killed 62 students found that:

• In 59% of the fatal fires, at least one student who died had been drinking
• In 28% of the fires the smoke detector was absent or had been disconnected
• 66% of the victims were juniors or seniors
• 65% of the victims were male
• 25% of the fatal fires occurred following a party
• In 21 of the cases where an autopsy indicated the blood alcohol content, the average was 0.12 with a high of 0.304
• Over half, 56%, of the fires occurred on the two weekend days, Saturday or Sunday, with 44% occurring during the rest of the week

Some of the most compelling research on the impact of alcohol on fire safety is being conducted by Dr. Dorothy Bruck and Michelle Ball from Victoria University in Melbourne, Australia. In a study conducted by Bruck and Ball, students were given controlled amounts of alcohol to drink and then allowed to fall asleep in their own beds. Once they were fully asleep, they were exposed to gradually increasing levels of sound that simulate smoke alarms and their response was measured. Their response while sober was measured to determine a baseline response as well as their response at 0.05 BAC and 0.08 BAC.

It was found that when students have been drinking it takes a much louder alarm sounding (95 dBA) to respond to smoke alarms than when they are sober. The normal smoke alarm is required to sound at 75 decibels (dBA) at the pillow.

What was troubling is the low level of inebriation (0.05 BAC) that caused the response capability to significantly deteriorate. In 36% of the trials the test subject did not respond until the alarm level was at 95 dBA or did not respond at all when they were at 0.05 BAC. This increased to 42% at the 0.08 BAC.

What is notable is that while the response capability decreases as the blood alcohol level increases, it is not as significant as the increase from sobriety to 0.05 BAC. In other words, it does not take much alcohol to cause a significant decrease in the ability to react to an alarm. According to the study, “The meaning of this is that even at what many would consider to be low to moderate levels, alcohol can seriously affect a sleeping person’s ability to respond to their smoke alarm. In fact, many participants reported feeling only slightly ‘tipsy’ at bedtime in the 0.05 BAC condition.”

The report lists a number of ways that alcohol impairment can impact upon a person’s response (or non-response) to a fire alarm, including:

• Failure to hear alarm
• Failure to correctly interpret alarm
• Inappropriate response, such as a failure to avoid a dangerous pathway
• Poor motor functioning, e.g., poor balance and coordination
• Recovery rate from burns is significantly worse for alcoholics, meaning that they may suffer death from more minor injuries than non-alcoholics.

A number of studies have been done over the years to determine the speed with which people will move horizontally and down stairs, particularly in relation to the age of the person. For example, a 30-year-old female would move at a horizontal speed of 235 feet/minute while a 70-year-old female would travel the same route at approximately 148 feet/minute. This correlates directly to determining a reasonable tenability time.

The NIST report gave several scenarios involving total escape time, and the one that fits the closest to an off-campus housing situation would be that of a young family at night with a total escape time of 90 seconds.

Conclusion

The NIST study reported that, on average, the alarms sounded before untenable conditions were reached, but not in all situations. As would be expected, greater escape times (i.e. earlier alarm activation) occurred with better smoke alarm placement and coverage, such as smoke alarms on every level and in every bedroom.

There is an incredible amount of information included in the NIST report about the performance of smoke alarms under different conditions, locations, etc. Unfortunately, the information is incomplete in terms of helping to identify the optimal type of detector to use.

Several of the major fire safety organizations in the country have offered their recommendations on what type of smoke alarm to use. The National Fire Protection Association, the International Association of Fire Chiefs and Underwriters Laboratories all recommend the use of both types of technology in the home to provide the optimal level of protection. However, the problem is determining what type of detector to use in what specific location. Given that NIST reports that the majority of fire deaths are caused by smoldering fires in the living room and bedroom, then that would lead to the conclusion that photoelectric smoke alarms are called for in those locations. (Keep in mind that this data is from 1992 to 1996.)

One of the five leading causes of fatal fires is flaming fires in the kitchen, which would seem to indicate that an ionization smoke alarm would be appropriate. However, it is widely recognized that ionization smoke alarms are susceptible to false activations from cooking smoke, which leads people to either remove or disable them. Fire professionals and the NIST study do not recommend the use of ionization smoke alarms in these areas for just this reason and call for using photoelectric.

The report goes on to state, “In many cases, available escape time would be sufficient only if households follow the advice of fire safety educators, including sleeping with doors closed while using interconnected smoke alarms to provide audible alarm in each bedroom, and pre-planning and practicing escape so as to minimize pre-movement and movement times during egress.”

The value of each of these recommendations is widely recognized. However, in “real world” scenarios, it is questionable if they are applicable. For example, many of the off-campus homes where students live are older buildings which may not be equipped with interconnected smoke alarms throughout the building. According to the USA TODAY study, 69 percent of the houses where the fatal fires had occurred had been built prior to 1930. While wireless interconnected smoke alarms available and a potential solution to the interconnectivity problem, they are only available using ionization technology, not photoelectric.

Furthermore, with the potential for delayed reaction time and egress because of alcohol impairment, tenability times may be reached before the occupants can react appropriately. This leads back to the need for the earliest detection time possible, coupled with widespread alerting throughout the building.

Unfortunately, the issue of dual-sensor smoke alarms was not resolved in this study. Some fire professionals (including the author) were advocating the use of these detectors as an alternative to stand-alone detectors. However, the results initially reported by NIST indicated a poorer performance by these types of units than stand-alone smoke alarms. As stated earlier, NIST indicated that these results were erroneously reported and that the report will have to be modified again to eliminate any potential for confusion. The additional information provided to Campus Firewatch does seem to indicate that these types of units may mirror the effectiveness of the stand-alone detectors, but it would appear more study and scrutiny is needed before reaching a conclusion.

Both Underwriters Laboratories and NFPA are looking into the issues surrounding photoelectric and ionization smoke alarms. The NFPA committee that oversees the standards for smoke alarms has formed a task force that will be producing information on this topic within the next few months, according to Chris Dubay, vice president for Codes and Standards at NFPA.

The bottom line is that it would appear at this time that there are no clear-cut answers as to what is the best type of detection to employ in a typical off-campus house.

• Photoelectric smoke alarms provide better detection of smoldering fires
• Ionization smoke alarms are better at sensing open-flaming fires.
• A majority of the fatal off-campus fires occurred in homes built prior to 1930 which do not lend themselves to being widely equipped with interconnected smoke alarms on every level and in every bedroom, which provides the optimal level of protection
• Interconnected smoke alarms will sound an alarm throughout a house, yet most of the ones on the market (particularly the wireless models) are ionization.
• The two top leading fatal fire scenarios identified by NIST are smoldering fires which would indicate the use of photoelectric smoke alarms.
• The leading fire safety organizations recommend the use of both types of technology in a home, but are silent on how they should be employed.

The most important part of all of this controversy, however, is that a working smoke alarm is undoubtedly a vital part of providing for a safer fire environment. Until these questions are resolved, it is critical to stress to the public the importance of having working smoke alarms present. We know that smoke alarms save lives – there may just possibly be an improvement upon this proven, life-saving technology.

More information can be found at the following websites:

NIST Smoke Alarm Study
http://smokealarm.nist.gov/

International Association of Fire Chiefs Fire and Life Safety Section Position Paper
http://www.iafc.org/associations/4685/files/FLSS_Position_Paper_smoke_alarms.pdf

National Fire Protection Association
www.nfpa.org/smokealarms

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