Technology that increases the speed at which smoke and fire is accurately detected, as well as eliminates nuisance alarms, can have profound benefits. According to NFPA, nuisance alarms are the leading cause for home dwellers to intentionally disable their smoke alarms. About two-thirds of fire deaths occur in homes without a functioning smoke alarm.

How to End the Smoke Detection Debate

In 1991, a recommendation was made to the NFPA Steering Committee for Smoke Detection Technology for a tighter test regimen that (if detectors could pass) would eliminate the controversy surrounding photoelectric and ionization technologies. The assessment proposed two changes to the UL 217 large-scale fire tests: shorten the UL smoldering fire test time allowed to less than 40 minutes from the current 75 minutes; and light the paper fire test from the top, not the bottom.

Detector technology at that time could not pass both of these revised tests. The photoelectric devices would not have enough visible smoke in the paper test, and the ionization devices would not have enough time in the smoldering test. The purpose of the recommendations was to set a standard of excellence that manufacturers would have to work diligently to meet. New technology would have to be developed, but at least there would have been a target.

While the recommendations were not adopted at the time they may still come to fruition. They would establish a new category of detectors capable of equaling detection times in flaming fires and substantially improving detection times in smoldering fires. Additionally, these new detectors could be set with lower sensitivities making them less susceptible to nuisance alarms. These devices can be set with lower sensitivities because they do not have to be set to high sensitivities to detect smoldering fires any longer. False alarms will be reduced.

Photoelectric detectors may not survive this test regimen, but there are accounts of multiple flaming fires (residential and commercial) during which the ion detectors went off quickly. Had it not been for the speed of the ion detector activation, the negligible damage would have been much worse.

Furthermore, when these fires were detected there was hardly any visible smoke and what damage there was would have resulted in little to no financial loss. Thus, it is reasonable to conclude that a photo detector would not have alarmed until these fires were much larger and considerably more damage was done.

Once detectors are required to pass these two revised tests, not only would the controversy finally be put to bed but the following benefits would result:

• Faster fire detection over a broader range of types of fires
• Fewer nuisance alarms than with current ion detectors because sensitivities can be set lower
• Lower cost than photoelectric or combo detectors
• Fewer models stocked by stores
• Less confusion for fire officials and buyers

Instituting a more stringent test protocol would revitalize fire protection efforts anew with the ultimate goal o
f saving more lives.

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Ion vs. Photoelectric: A Historical View

Smoke detection arrived in the United States in 1951 when Cerberus GmbH of Switzerland signed a contract with the manufacturer CO-Two for distribution of the Cerberus ionization smoke detector. Following is a partial historical account of fire detection development in the U.S. since then, including some key bulleted dates.

1958 — A fire at Our Lady of the Angels, a Catholic elementary school in Chicago, claimed the lives of 92 children and three teachers. The tragedy inspired a massive call for better and more sensitive fire detection.

1967 — The National Fire Protection Association (NFPA) published a guide for residential fire detection, which recommended a heat detector in every room wired to a control panel. No mention of smoke detectors was made in the document.

1969 — BRK Electronics of Aurora, Ill., received a UL Listing for a battery-operated smoke detector (SS69H) utilizing a resistance-grid sensor and heat detectors. The device, which could be mounted on a wall or ceiling, was actually listed as a “control panel.”

1970 — Statitrol Corp. developed and sold a battery-operated ionization smoke detector. This was followed by AC-operated photoelectric smoke detectors from Pyrotector and Electro Signal Labs (ESL).

1974 — NFPA 74 (“Standard on the Installation, Maintenance and Use of Household Fire Warning Equipment”) was issued, opening the market for residential smoke detection with single-station detectors that no longer had to be wired to a control panel.

The ability to sell UL-Listed, single-station smoke detectors led to a flood of brands entering the market, including GE, Gillette, Norelco and First Alert. All of these products were ionization-type detectors. The percentage of homes outfitted with smoke detectors rocketed from a miniscule number in 1970 to greater than 50% by 1980.

The manufacturers of photoelectric type detectors were hungry to get a share of the market. Their approach: show that photo detectors are better at detecting smoldering fires. They did this by staging demonstrations where cotton was placed on a light bulb and allowed to smolder. Hence began the controversy between the two device types.

At the urging of many stakeholders in the 1970s, UL decided to combine the commercial test standards that governed ionization and photoelectric technologies. The objective was to combine UL 168 (Commercial Photoelectric Smoke Detectors) and UL 167 (Commercial Ionization Smoke Detectors) into one standard that would cover single and multiple-station detectors.

The toughest task was to include large-scale fire tests that both types of sensors could respond to within prescribed time limits. UL 168 had never had full-scale fire test requirements. The new standard was to be UL 217, Single and Multiple-station Smoke Alarms.

In 1974, UL ran fire tests to determine the ability of each type of detector to pass. Six test scenarios were attempted with different materials: shredded paper, polystyrene, gasoline, wood, cotton and polyurethane. Both types of sensors responded well enough to the polystyrene, gasoline and polyurethane fires; however, there were detection issues with the other three materials.

The conclusion, as reported by UL, was unambiguous: “ … neither detector does well in all types of fires.” This only added more proverbial fuel to the growing dispute between the technologies. Thus, the tests were significantly modified so that each type of technology could pass the shredded paper and wood brand tests. Doing so allowed one standard to be released with the understanding that “neither detector does well in all types of fires,” according to a UL report.

Throughout the 1970s manufacturers of each technology battled for market share. White papers were published and skewed demonstrations performed. Lawsuits amounting to millions of dollars were pursued when smoke detectors did not “alarm fast enough.” And most significantly, confusion reigned among the fire protection community as well as with end users.

The 1980s witnessed the release of a detector that had both an ionization sensor and a photoelectric sensor in one unit. It attempted to solve the controversy except that its high price point hampered the device’s market share potential. Comparatively, by the late 1980s the basic ionization models had fallen below $10.

In the 1990s the requirements for a detector in each bedroom was added to UL 217, as well as the requirement that all hardwired detectors had to have battery backup. Still no one had developed an inexpensive detector that quickly detects both smoldering and flaming fires.

Among the objectives of a smoke characterization study conducted by UL in 2007 were to develop recommendations to UL 217 and allow for the development of new smoke-sensing technologies. As a result of UL’s project, the following was identified for future consideration: “Requiring the use of combination ionization and photoelectric alarms for residential use in order to maximize responsiveness to a broad range of fires.”

The reason for this recommendation was that “Some of the evaluated flaming and non-flaming test scenarios triggered one but not both photo and ion alarms within the alarm response time criteria specified in UL 217.”

Hence, the controversy perpetuates today.

Fred Conforti is former CEO of the Pittway Systems Technology Group (PSTG). He can be contacted at fl.conforti@yahoo.com.

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