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Greg Kessinger is SD&I's longtime fire and life safety writer.
Q. Popular Mechanics magazine recently listed “101 Gadgets That Changed the World.” Among all the creative and wonderful inventions you will find, among them is the automatic smoke detector. However, certain other discoveries and developments obviously had to occur before the smoke detector, which we now take for granted, would become widely available, correct?
A. From what I’ve been able to research, around the mid 1920s a Swiss scientist named Heinrich Greinacher developed the voltage multiplier circuit and cascading generator which led to his development of the ionization chamber which would ionize air. Part of this process involved subjecting a gas to a grid of wires through which streaming high voltage current passed. With this new fundamental knowledge of ionization chamber technology, another Swiss scientist named Walter Jaeger attempted to create a poison gas detector based on Greinacher’s earlier work. While Jaeger didn’t succeed with his poison gas detector he did notice that it worked very well for detecting smoke. Consequently, Jaeger and his partner eventually ended up developing and marketing a commercial ionization smoke detector around 1947. Similar to the few flying cars that have been ‘invented,’ it was not very practical (since it needed 220 volts of power) and it was expensive.
Around 1944 Glenn Seaborg, a Michigan native, took time off from his regular job at the University of California to work on the Manhattan Project in Chicago. During this period, Glenn Seaborg and his team of other gifted nuclear chemists are credited with the discovery of Elements #90 through #102 on the Periodic Table of Elements. Using an isotope called Americium–241, Element #95, allowed them to develop a new type of ionization chamber, without the need for the high-voltage fields of Greinacher’s day. In 1962, the U.S. Atomic Energy Commission began selling Americium-241 for about $1,500 per gram, which was enough to make about four million ionization smoke detectors. A little does go a long way and because so little is used in each detector, regular disposal in a landfill is permitted. However, inhaling its dust from crushing or burning the Americium-241 bits is considered carcinogenic.
In 1964, Duane D. Pearsall was developing an ionization chamber which he hoped would be used to alert photographic developers of dangerous static electricity levels. Like the Swiss more than a generation earlier, he found his invention detected smoke particles better. However, unlike the Swiss, his standalone device operated using Americium-241 as the ionization source. He also made his to operate on special rechargeable batteries. Purchased by Emerson Electric and eventually by BRK Electronics, these first smoke alarms were sold nationally by Sears Roebuck and Company beginning in 1974. Pearsall’s invention was not expensive, easy to install and through the use of mass marketing, these devices began saving thousands of lives.
Also about this time, NASA requested Honeywell to develop an adjustable smoke alarm for use in the space program using the ionization principle, and their task was much easier in the age of transistors. While I imagine their first prototype to be one of the most expensive smoke detectors ever made, Honeywell was able to create the requested ‘gadget’ which was powered using only 24 volts DC. The adjustability allowed them to set it for maximum protection under a wider range of conditions in orbit.
Since 1964, the low-voltage electronics market has developed more advanced ionization and photo electronic smoke detector and smoke alarm models. National awareness of their importance to life safety has propelled them to the head of many “top 100 inventions of our time” lists. If it were up to me, I would give credit for the first practical and successful smoke detection “gadget” to two ‘Wolverines”: Duane D. Pearsall, also a Michigan native, for inventing the single station battery powered “smoke detector,” which used Glenn Seaborg’s Americium-241 to ionize rather than high-voltage electricity. Duane D. Pearsall passed away in 2010 but if you visit Youtube.com you can view an 11-minute documentary video made by Pearsall’s daughter, where she demonstrates his first inventions. You will even learn the secret behind their widely recognized shape.
Greg Kessinger is SD&I’s longtime resident fire alarm and codes expert. His column is the longest, continually running contribution in the 34-year history of the magazine. He can be reached at firstname.lastname@example.org.