NFPA Journal - March/April 2013 - (Page 57)

The Photoelectric–Ionization Debate WHILe ResIdentIAL sMoke ALARMs like statitrol’s smokeGard have clearly played an important life safety role since they were introduced, the debate over the relative effectiveness of the different detection technologies has continued for years. the ionization-type smokeGard may have brought innovations to the smoke detector market when it was introduced in the early 1970s, for example, but it wasn’t alone. Photoelectric-type alarms were also being introduced around the same time the smokeGard debuted, and other ionizationtype alarms followed, too. soon an array of manufacturers were jumping at the chance to sell affordable, easy-to-install, “single-station” detectors to American homeowners, many of whom were newly aware of home fire hazards as a result of media attention around the 1973 America Burning report. As the battle in the marketplace heated up, questions arose over which technology was more effective. Ionization-type smoke alarms have a small amount of radioactive material between two electrically charged plates, which ionizes the air and causes current to flow between the plates. When smoke enters the chamber, it disrupts the flow pioneer Richard Whitcomb. Duane Pearsall is on my short list of the most brilliant people I have ever met. A quiet and humble man, he was also profoundly civic-minded. He was a leader in the U.S. Chamber of Commerce and cofounded its Small Business Council. (In 1976, well before the true impact of the home smoke detector was known, he was named Small Business Person of the Year by the U.S. Small Business Administration.) He was frequently invited to speak on small business issues before Congressional committees, federal agencies, and university and business groups. Pearsall died in 2010 at the age of 88, and to his last day he sought to give back to the community he always felt gave so much to him. And through the development of an affordable, easy-touse home smoke detector, he also had the greatest impact on fire deaths of any other person I can think of. He would be the first to tell you he didn’t do it alone, but it was Pearsall who brought the vision, passion, dogged commitment, resources, diplomacy, and entrepreneurial skills to the cause and made it happen. of ions, thus reducing the flow of current and activating the alarm. this type of detection is generally more responsive to the invisible particles produced by flaming fires. Photoelectric-type alarms aim a light source into a sensing chamber at an angle away from the sensor. smoke enters the chamber, reflecting light onto the light sensor and triggering the alarm. Photoelectric smoke detection is generally more responsive to the visible particles produced by fires that begin with a long period of smoldering. nFPA’s smoke alarm requirements are included in nFPA 72®, National Fire Alarm and Signaling Code, which does not specify either technology, with one exception: When the alarm is near cooking appliances, the code calls for either a photoelectric-type alarm, or any type of alarm if it has a hush feature. since ionization smoke alarms are generally more responsive to flaming fires, and photoelectric smoke alarms are generally more responsive to smoldering fires, nFPA recommends that both types of alarms, or a combination photoelectric-ionization alarm, should be installed in homes for the best protection. For more on smoke alarms visit nfpa.org/alarms. Fire deaths began to decline soon after home smoke detectors hit the market. Thirty years later, U.S. fire deaths had dropped by half, achieving one of the primary goals spelled out in the 1973 America Burning report, and the per capita death rate had undergone an even greater reduction. It is estimated that that some 60,000 deaths did not occur that would have, had the death rate remained constant over those three decades. While the decline in fire deaths can be attributed to a number of factors, including a reduction in cigarette smoking, there can be little question that the home smoke detector has had a major impact. Over that same period, according to NFPA statistics, the percentage of homes equipped with smoke detectors increased from fewer than 4 percent to 94 percent. Today, self-monitoring battery-powered home smoke alarms can be purchased for less than $10. In his memoir, Pearsall writes about the first documented report that a SmokeGard detector had helped save lives in a home fire. It was 1975, and he got a call one morning at his office from Rexford Wilson, whose consulting company was located outside Boston. Wilson started to tell him the story of a Massachusetts family that had just survived a house fire, but Pearsall interrupted him to broadcast the call over the public address system in the Statitrol plant. As workers listened, Wilson told them that he had a burned and shriveled SmokeGard in his office that had been recovered from a house fire two days earlier. The alarm had sounded in the middle of the night, and a family of three, along with their dog, had escaped. The quality control inspector number, 5602, was stamped on the detector, and Wilson congratulated the employee who’d conducted the inspection. Pearsall offered a few words of gratitude to his employees over the PA system, he writes, and as soon as he finished speaking, “wild applause followed” from the plant. That seems like a fitting response to the legacy Duane Pearsall left behind. DaviD a. Lucht was the first head of the graduate program in fire protection engineering at Worcester Polytechnic Institute in Worcester, Massachusetts. MARCH/APRIL 2013 NFPA JOURNAL 57 http://www.nfpa.org/alarms

Table of Contents for the Digital Edition of NFPA Journal - March/April 2013

NFPA Journal - March/April 2013
Contents
First Word
In a Flash
Perspectives
Firewatch
Research
Heads Up
Structural Ops
In Compliance
Buzzwords
Outreach
Electrical Safety
Wildfire Watch
Cover Story: Storage Occupancies
Fifty Years of Smoke Detection
Industrial Occupancies
Chicago 2013
Fire Analysis + Research
Section Spotlight
What’s Hot
Looking Back

NFPA Journal - March/April 2013