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The Most Important Technological Breakthrough of the 20th Century

The Most Important Technological Breakthrough of the 20th Century

By David A. Lucht, P.E., FSFPE

The world of fire protection has seen several technological game changers over the centuries. The first was the automatic fire sprinkler invented in 1874 by Henry S. Parmalee, a piano manufacturer in New Haven, Conn.1 With improvements by the likes of railroad locomotive designer Frederick Grinnell, this new technology soon evolved to have profound impact on an epidemic of industrial fire losses, particularly in New England textile mills of the 19th Century.

A hundred years later, another breakthrough came along in the form of the affordable home smoke alarm. As was the case for the sprinkler, there was a massive fire problem to be solved. Interestingly, the breakthrough came from a person outside the fire community. He wasn't a fire protection equipment manufacturer, fire protection engineer, or fire researcher. He was a small business person manufacturing electrostatic control equipment in Lakewood, Colo. And he stumbled on the idea by accident.


In 1973, the National Commission on Fire Prevention and Control reported that the U.S. had the highest per capita fire death rate in the industrialized world.2 While different reporting practices made international comparisons difficult, fire death rates were reported as twice that of second-rated Canada, three times the U.K., four times Japan and more than 10 times France and Italy.3

Soon after the home smoke detector hit the marketplace in the 1970s, fire deaths began to decline. Thirty years later, American fire deaths had fallen 50%. The per capita death rate had dropped by nearly two thirds-from 35 deaths per million population down to 13 (Figures 1 and 2). It's estimated that some 60,000 fire deaths did not occur that would have if the death rate had remained constant over these three decades.

Figure 1: Civilian Fire Deaths
Source: Karter, M.J., Fire Loss in the United States During 2012, NFPA September, 2013

Figure 2: Civilian Fire Death Rate
Source: Trends and Patterns of U.S. Fire Losses in 2012, NFPA November, 2013

While the decline in fire deaths can be attributed to a number of factors (such as reductions in cigarette smoking), there can be little question the affordable home smoke alarm had a major impact. Over the same 30-year period, the number of households having smoke detectors increased from fewer than 4% to 94% (Figure 3).

Figure 3: Percent of Households with Smoke Alarms
Source: Ahrens, M., Smoke Alarms in U.S. Home Fires, NFPA September, 2011 (1977-2012), Hall, J., A Brief History of Home Smoke Alarms, NFPA May, 2000 (1970-1976 est)


The story began in the 1960s when young entrepreneur Duane Pearsall was busily at work starting up his first successful manufacturing company called Statitrol Corporation. His product was designed to eliminate static electricity problems. This was of particular interest to industries such as newspaper printing, photo and data processing operations. The operating principle was to discharge negative ions into rooms and spaces, thereby preventing static electricity discharges. It was simply an ion generator.

Things were going well and the company was starting to turn a profit. Then disaster loomed. Customers were complaining of product failures in the field. Something had to be done, and done fast. Nothing could have been further from Pearsall's attention than smoke detectors.

Pearsall called in his engineer/inventor consultant, Lyman Blackwell, to help figure out why the ion generator was misbehaving. In Pearsall's words, "Lyman kludged together" a makeshift lab experiment to measure the flow of ions in the airstream discharging from the generator.*

* Quotes and other specific attributions to Duane Pearsall are taken from his memoir titled My Life Unfolded, published by the Pearsall family in 2009.

Not long after the experiment was powered up, the ion concentration meter began showing erratic readings that, at first, could not be explained. Soon, however, Pearsall recalled that the strange readings only happened when Randy the lab technician was in the room. Randy was a compulsive chain smoker, sometimes lighting up at the most inappropriate times. It became clear that the lab instruments were detecting invisible smoke particles. Someone jokingly remarked, "We should be making smoke detectors!" According to Pearsall's memoir, this was the " point of discovery ... the embryonic beginning of the battery-operated home smoke detector."

With no experience in the field, Pearsall set out to develop a smoke detection business. First to emerge was a new hard-wired commercial system designed and patented by Blackwell using dual ionization chambers and energy-saving inverted triode technology, which he had also invented several years earlier.4 Introduced in 1968, the Statitrol system only required a 24 volt power supply as opposed to the higher power requirements of other systems in the marketplace (220 volts).

The low voltage, hard-wired systems were still too costly for the average homeowner, especially for retrofitting existing homes. Pearsall forged ahead to develop what would ultimately be a completely self-contained battery powered home smoke alarm system about the size of a coffee cup that could easily be attached to the ceiling with two screws. Once again, Blackwell contributed to the technological design. His innovative use of the Complementary Metal Oxide Semiconductor (CMOS) further reduced electrical power requirements, helping to make the battery energy source feasible.

Finally, Pearsall was concerned about the possibility of the batteries going dead and disabling the detector, leaving dwelling occupants unprotected. To guard against this, Blackwell and Statitrol's staff engineer, Paul Staby, developed and patented self-monitoring circuitry that would cause an audible warning when the battery strength deteriorated.5 This would end up being a key feature for overcoming resistance to the self-powered concept.


Pearsall had had the "aha moment." He had a vision. He had a prototype and team of experts at the ready. Now, using his considerable leadership skills in the business of product development, engineering, manufacturing, marketing, distribution and sales, he was ready to make the low cost, self-contained battery powered smoke detection system a reality. He would call it the " SmokeGard."*

* Due to OEM agreements and corporate purchases and sales, over the years Statitrol technology has appeared under several names

Pearsall quickly learned that a labyrinth of hurdles lay ahead in the journey toward actual retail sales. These included:

  • Laboratory approval. Before retail sales could begin, the mark of approval was needed from a recognized testing laboratory. Underwriters Laboratories declined to test the product since the consensus standards of the day did not permit single station, battery-powered devices.
  • Consensus Standards. NFPA Standard No. 74 Household Fire Warning Equipment did not allow the battery-powered device. Changes would have to be made.
  • Fire service Opposition. Of surprise to Pearsall was opposition by many local, state, and national fire service leaders. Concerns would have to be overcome.
  • Code Requirements. Very often, sales of fire protection devices are heavily driven by state and local code requirements and the consensus model codes upon which they are based. None of the model codes recognized the battery power concept. Nor did they require detection systems in dwellings. Amendments would be needed.

With plenty of serious challenges to overcome, Pearsall set out to make the product feasible. While he was personally involved every step of the way, part of his genius was an exceptional ability to harness the involvement of other enthusiastic talents- ranging from engineers and marketing professionals to dedicated rank and file factory workers and public service advocates.

He assembled an ad hoc cluster of fire community members to help him promote understanding and resolve concerns among fire and building professionals. This included Rexford Wilson, consulting fire protection engineer; Denver Fire Chief Myrle Wise; and John "Gus" Degenkolb, retired Los Angeles Fire Department officer and code consultant. Together they talked up the idea, answered technical questions and distributed free prototypes of the detector to movers and shakers in the world of fire safety.


With ample support from national advocates for the low-cost home smoke detector, speedy progress was made by the Technical Committee responsible for NFPA No. 74 Household Fire Warning Equipment.6 The standard was amended in 1972 to accommodate the self-monitoring battery power. The new language read as follows:

2030. Primary Power Supply (Monitored Battery)

2031. Household fire warning equipment may be powered by a battery provided the battery be monitored to assure that the following conditions are met:

  1. All power requirements are met for at least one year's life, including routine testing.
  2. A distinctive audible trouble signal shall be given before the battery is incapable of operating (from aging, terminal corrosion, etc.) the device(s) for alarm purposes.
  3. Following an alarm in which the battery(s) reaches its trouble point, the trouble signal shall operate for at least seven consecutive days.
  4. The audible trouble signal is produced at least every minute for seven consecutive days.
  5. The monitored batteries meeting these specifications shall be clearly identified on the unit or the battery compartment.

Changes were also undertaken to modify the number of detectors required. At the time, NFPA 74 required smoke detectors in the hallway outside bedrooms and heat detectors "in all rooms, all closets, and in all other areas where fires can occur." These requirements resulted in system costs that were prohibitive for the homeowner.

Richard Bright, a leading detection researcher at the National Bureau of Standards (now National Institute of Standards and Technology), estimated a cost of $700 to $1,200 to protect a typical three-bedroom home in 1974.7 The cost factor helped define Pearsall's target..."to perfect a lifesaving product every homeowner could afford."

By this time, empirical fire research was beginning to show that smoke detectors alone provided a high rate of return in terms of lives saved vs. system costs compared to heat detectors. The 1972 edition of NFPA 74 gave a nod to this fact by acknowledging for the first time that heat detectors need not be mandatory in all rooms, closets, and other areas:

2412. This standard recognizes that the use of partial protection can provide some degree of life safety for sleeping occupants when a basic smoke detector is installed in the immediate area(s) of, but outside of, the bedroom(s).

A few years later, Bright reported "...the 1974 edition of NFPA No. 74, however, recognized the fact that smoke detector technology has advanced to the point where the judicious installation of one or two smoke detectors could be more effective than a house full of heat detectors in alerting dwelling occupants to fire."8


Just as Pearsall was beginning to see some light at the end of the tunnel, consumer advocate Ralph Nader threw up yet another roadblock. In 1976, Nader filed a complaint with the Nuclear Regulatory Commission (NRC) claiming the ionization smoke detectors produced radioactive emissions that were hazardous to the health of people in buildings. He petitioned the NRC to recall the detectors and ban further sales.

The SmokeGard did contain a small radioactive source for the purpose of creating ions in the detection chamber¼ as is the case for all ionization smoke detectors. Sensitive to the health concern, Pearsall had already changed the radioactive source from 0.5 microcuries of Radium 226 to 1.0 microcurie of Americium 241, which was deemed to be even more benign.

The NRC dismissed the claim, noting a person receives 100 times more background radiation due to high elevation flying round trip across the U.S. With a lot of public education effort, Pearsall was able to move forward and conquer yet another hurdle.


Interestingly, the first laboratory approval of the battery-powered home smoke detector came from Factory Mutual Laboratories (now known as FM Approvals), which had never in its 136-year history tested and approved a household product. FM Approvals had always focused exclusively on fire equipment for industrial and commercial applictions.

Pearsall and his team would leave no stone unturned, approaching FM despite the fact that the laboratory had no history of testing home safety products. As it turned out, management took an interest, due in no small measure to altristic motives of individual FM personnel. In a 1971 internal memorandum from Approvals Manager Eugene Cray to Vice President Jack Rhodes, Cray reported an increase in requests for fire alarm systems, in direct proportion to public and government officials' growing concern over the appalling loss of life resulting from home fires. Cray recommended that FM Approvals move into the home fire alarm certification business.

Within weeks, a new residential approval category was authorized by management and, with technical assistance from Rexford Wilson, tests of the Statitrol SmokeGard Model 700 were undertaken. FM approval was achieved in 1972. At about the same time, SmokeGard made its retail debut in the Sears & Roebuck Spring Catalog at a list price of $37.88.

Underwriters Laboratories tested and listed the SmokeGard in 1974.

Duane Pearsall
1922 - 2010
SFPE Person of the Year - 1980


With support from the likes of Wilson and Degenkolb, Pearsall first concentrated on the western U.S. region through the International Conference of Building Officials. ICBO was the first model code to incorporate requirements for smoke detectors in the hallways immediately outside bedrooms. With additional advocacy nationwide, others followed:

  • 1973 - International Conference of Building Officials*, ICBO Uniform Building Code
  • 1975 - Building Officials and Code Administrators*, BOCA Basic Building Code
  • 1975 - Southern Building Code Congress*, SBCCI Standard Building Code
  • 1975 - Council of American Building Officials, CABO One- and Two-Family Dwelling Code
  • 1976 - National Fire Protection Association, NFPA 101, Life Safety Code (Tentative Interim Amendment issued in 1973)

*Later merged to form the International Code Council

Soon state and local governments started adopting the model codes for new construction. Some implemented self-standing home fire alarm laws and ordinances. Ohio adopted the first state-wide requirement in 1971.9

As time went on, lawmakers ventured into retroactive regulations for existing homes, usually requiring installation of smoke detectors at the time of a purchase and sale agreement. The easy-to-install, battery-operated device pioneered by Pearsall made i t feasible to retrofit the nation's vast inventory of existing residential building stock. In 1970, virtually none of the 63 million U.S. households were protected. Remarkably, smoke alarms would be installed in more than 90 million homes over the following three decades. (By the year 2000, the total inventory grew to 105 million households.)10

Pearsall made good progress with his smoke alarm business in a relatively short time- at its peak Statitrol had some 1,000 employees turning out smoke detectors. But he would be the first to tell you he didn't do it alone. He depended heavily on Lyman Blackwell for his key role in technical design and had help from a host of other engineers, code advisors, public officials, and people of good will. But he brought the vision, the passion, dogged comitment, resources, diplomacy, and entrepreneurial skills to the cause. He was the point man who did more than anyone to bring about this 20th Century breakthrough in life-saving technology.

David A. Lucht is a Professor & Director Emeritus, Fire Protection Engineering Department, Worchester Polytechnic Institute.


  1. Fitzgerald, Paul, Mawhinney, John, Slye, Orville, Water-Based Fire Suppression, History of Fire Protection Engineering, (J. Kenneth Richardson, Editor), SFPE/NFPA, 2003.
  2. "America Burning: The Report of the National Commission on Fire Prevention and Control", U.S. Government Printing Office, 1973.
  3. "International Fire Statistics, 1972," Fire Journal, NFPA, Nov. 1973.
  4. Blackwell, Lyman L., "Aerosol Detection Device," United States Patent 4093886A, July 6, 1976.
  5. Blackwell, Lyman L. & Staby, Paul A., "Self-Monitoring Battery Operated Circuit," United States Patent 3778800, April 9, 1971.
  6. NFPA No. 74, Household Fire Warning Equipment, NFPA, 1972 Ed.
  7. Bright, Richard G., Fire Journal, NFPA, Nov., 1974.
  8. Ibid
  9. Lucht, David A., "Legal Requirements for Fire Alarms in Ohio Dwellings," Fire Journal, NFPA, March, 1972.
  10. Statistical Abstract of the United States, U.S. Census Bureau, 2012.