09-03-2006, 03:29 PM #1
- Join Date
- Nov 2002
iONIZATION VS, PHOTOELECTRIC SMOKE DETECTORS
I am curious to know how many people in Fire Prevention and Public education are aware of the following. Please provide feedback. Thanks.
ISSUE ONE: ION DETECTORS GO OF TOO LATE IN SMOLDERING STARTED FIRES
According to the USFA approximately 40% (1,200 people per year) died when detector operates.
Now gop to the following website (htp://smokealarm.nist.gov/HSAT.pdf). It is a report done by the National Institute of Standrads and Technology that summarizes the results of some fire testing they did.
On Page 75-76 (101-102 on the internet) it shows a diagram of the 2 story house they used. On page 243 (269 on the internet) it shows the results for that house. I have summarized them below. Note that for the smoldering fire started in the Living Room the Ionization detector is providing at best 16 seconds warning and at worst ig going off 54 seconds after it is too late. (Sound familiar to last year fire.) The Photoelectric detector in the same scenarios is responding 40-55 minutes earlier!
ISUE TWO: THE % OF PEOPLE DYING WHEN THE SMOKE DETCTOR OPERATES HAS BEEN INCREASING SINCE THE LATE 80'S.
. Here is a summary of statistics from previous USFA Reports titled “Fire in the U.S.” Increase in fatal fires with working detectors – 1988 (9%), 1994 (19%), 1996 (21%), 1998 (29%), 2001 (39%). While there will always be a certain percentage of people who cannot be saved by smoke detectors, e.g. the handicapped, those intimate with the fire etc., there is no reason to believe that the number of those people quadrupled between 1988 and 2001. In addition, while the number of fires with working detectors increase approximately in proportion to the increase in the number of detectors installed, the increase in the % of fatal fires with working detectors far exceeds it.
In my opinion the best explanation is that starting in the late 80’s, Underwriters Labs, in an attempt to reduce nuisance alarms, forced the manufacturers to make less sensitive ionization detectors. Shortly after this change UL modified the smoldering test in UL217, the UL Smoke Detector Standard, in ways that made it much easier for the ionization detector to pass. The gradual introduction of these desensitized ionization detectors into American homes is the most reasonable explanation for the increase in fire deaths in cases where the detector operated. As a consequence this unrecognized flaw could be responsible for hundreds of deaths per year.
ISSUE THREE: ION DETECTOR ARE FAR MORE SUSCEPTIBLE TO NUISANCE ALARMS. T (20% (approx 600 people per year) died bacuse detector disable.)
In the study that took place in the Native American Community14 there were not a lot of photoelectric detectors used. To quote from the study,
"There were only three photoelectric detectors in our survey, none of which had nuisance alarms. One trailer had two of these detectors, each of which was paired with an ionization detector that was installed within 6 inches of it. Both of the ionization detectors sounded cooking nuisance alarms. In another home, the photoelectric detector was located 6 feet closer to the stove than an ionization detector, which had frequent alarms from cooking."
As a consequence of these types of observations the researchers concluded that,
... We favor photoelectric detectors to reduce rates of nuisance alarms from cooking and to provide optimal protection from cigarette related fires. Electrical detectors with battery back-up are the detectors of choice, except in communities such as remote villages in Alaska, where alternating current is non-existent or unreliable. If ionization detectors are installed, they should be located at least 20 feet, and preferably 25 feet, from stoves and at least 10 feet from bathroom doors if possible."
This is a complicated story. I do not want to send a message that smoke detectors do not work. Even ion are far better than nothing, But I do beleive that one type, photo or combinations, is far superior to the most common type, ion.
•Photolelectric detectors might reduce by 1/2 the # of people dying in fires, when the detector works. (This would be a 20% reduction.)
•Photelectric detectors might reduce the number of disabled detectors due to nuisance alarms. (Assume problem reduced by 1/2 - 10% reduction)
•It seems reasonable to assume that switching from ionization to photoelectric technology could save 960 lives (.30 * 3,200) per year!
This number could be higher, if # of fatalities that occur when no smoke detector present is over-estimated. (Many Chief's assume that if occupants died then the smoke detector wasn't there - go
09-04-2006, 10:20 PM #2
- Join Date
- Sep 2006
- New England
Photoelectric and ionization are designed for different applications. An ISD (ionization smoke detector) is for flaming fires or invisible smoke. It is designed to pick up particles less than <0.3 microns in size. Whereas a PSD (photoelectric smoke detector)is for smoldering fires or visible smoke. It is designed to pick up particles greater than >0.3 microns in size. Both are excellent for doing the job they are designed to do. It is very important that they be used in the correct application. A typical dwelling would normally have more material susceptable to a smoldering fire than a rapid flaming fire. The particles given off by normal household items ( drapes, couches, chairs, linnens, carpets etc..) are usually larger in size and when passed through the chamber of a photoelectric smoke will reflect more light than a high heat flaming fire. This of course will go into alarm sooner than the smaller particles of the flaming fire.
This being said I believe photoelectric smokes should be used primarily in dwelling units. The statistical numbers seem to reflect this as well. However the cost of a photoelectric smoke compared to an ionization is quite a bit higher. In new construction a builder is not likely to concern themselves with the protection aspects of the device but rather in meeting minimum code with minimal cost. A shame it may be but that is the current reality that I see. The individual AHJ's can make a huge impact in the stats by simply requiring photoelectric smokes in new dwellings. Over the next 10 years or so we may be able to see the death toll reduced due to the earlier warning of the photoelectric smokes. -TD
09-05-2006, 08:19 AM #3
- Join Date
- Nov 2002
Thanks for the feedback. More information on this topic can be found at interfire.org (search on "detector")
Of course the most important thing anyone can do is to make sure that whatever detector they have is operational but I have been lecturing for years that while ion are good the public should be told that photo are better.
I convinced Massachusetts to require photlectric within 20 feet of a kitchen or bathroom almost 10 years ago. I now have proposals before the Mass building Code Board to require photolectric in all residential.
Fortunately, others have already listened. Look at the following press release.
HOUSEHOLDERS ENCOURAGED TO PURCHASE PHOTO-ELECTRIC SMOKE ALARMS
Monday 5 June 2006
The Australasian Fire Authorities Council (AFAC) has today indicated that the more readily available ionisation smoke alarms purchased by most Australian householders may not be as effective, in all circumstances, as photo-electric smoke alarms.
These conclusions have been reached by AFAC as a result of early findings from research being conducted by the fire industry’s Cooperative Research Centre (CRC) on its behalf. The findings of this research conclude that photo-electric alarms are consistently more effective than ionisation alarms at detecting smouldering fires in homes.
“For some fires that occur in the home, such as smouldering fires, ionisation alarms may not alert occupants in time to escape safely. Photo-electric alarms increase the likelihood of all types of fire being detected in the home. This increases the likelihood that occupants will have enough time to escape,” said Len Foster, Chief Executive Officer, AFAC.
In a review of global literature, the research found that photo-electric alarms consistently provide sufficient time for occupants to escape from smouldering and flaming fires, provided the alarms are installed and maintained properly and the occupants hear them.
Until recently, consumers have been left to choose the most appropriate smoke alarms for their homes. Most consumers have chosen the cheaper and more common ionisation smoke alarm. This research indicates that although both ionisation and photo-electric smoke alarms provide
occupants time to escape, it concludes that photo-electric alarms should be promoted as the technology of choice.
Although in the past 30 years, ionisation alarms have helped to save the lives of hundreds of people in Australia and New Zealand, Mr Foster urged all householders to supplement their existing ionisation smoke alarms with photo-electric ones. For households that do not have smoke alarms, Mr Foster urged they be installed. He also urged householders to ensure that their smoke alarms work. “Unfortunately, those who are most at risk from fire are unlikely to have an alarm, or have removed the batteries.” he said.
Further details of AFAC’s position on smoke alarms for residential accommodation can be found
AFAC is the peak representative body for fire, emergency services and land management agencies in the Australasian region.
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