Technological Innovations Strengthen Reach of Detection

October 31, 2004 SSI Staff

There is nothing more important in the lives of everyday people than protection against fire and smoke. The life-safety industry has been busy over the past few decades as insurance companies, the government and the public are demanding faster, more reliable and accurate fire detection.

Equipment manufacturers have responded by working to provide products that are better and more dependable. New and improved sensors, as well as enhanced algorithms, work to reduce false alarms while improving detection time.

Such high-tech solutions must first be conceived in the mind, fabricated by custom means and perfected in the lab before they can be released to the public. In this month’s Fire Side Chat, we will talk about a number of innovations that are acting to improve the life-safety market, thus saving lives and reducing property damage.

Negating Nuisance Alarms
In the early years, when the life-safety industry sought to sell the public on the merits of smoke detectors, many salespeople used the catch phrase, “where there’s smoke, there’s fire.” Although most of the time this is true, there are times when what appears as smoke to a sensor may actually be something else. That can result in a nuisance alarm.

According to St. Charles, Ill.-based fire detection manufacturer System Sensor in a white paper entitled, “Reducing Detector-Based Nuisance Alarms,” nuisance alarms are not the same as false alarms. However, since nuisance alarms and false alarms both generate an alarm signal, the two terms are often interchanged. The difference lies in the fact that where a false alarm is the detection of something not there, a nuisance alarm is caused by conditions that, at the least, resemble smoke, but are not generated by heat or flames. There’s smoke, but no fire.

The primary mission of almost all smoke detectors is to detect life-threatening conditions in the environment. If a common smoke detector comes into contact with an airborne substance that resembles smoke but is not, a nuisance alarm can occur.

Advances in fire science, microprocessor technology, and firmware — combined with new and improved state-of-the-art, solid-state sensors — have rendered a means whereby detection is more assured while greatly reducing nuisance alarms. The result is greater detector reliability and growing public trust.

Sometime ago, equipment manufacturers in the life-safety market devised a means where smoke detectors — or the head-end systems to which they are connected — can detect a buildup of dust inside the smoke chamber. Such a buildup can cause unwanted alarms. The sensitivity level of the detector can be adjusted according to the amount of dust buildup inside the sensor. This feature, known as drift compensation, has greatly reduced nuisance alarms, but there was still room for improvement.

Equipment manufacturers continued the search for greater reductions in nuisance alarms. What they came up with, and what they continue to work on, is both surprising and effective.

Smoothing Out Output Spikes
One way to minimize nuisance alarms is through a method called smoothing algorithms. Smoke detectors are often exposed to airborne particles other than smoke particulates from an actual fire. Possible sources include dust particles, radio frequency (RF) interference, insects and high humidity levels.

Such conditions can cause rapidly changing spikes in the output of the smoke sensors inside of traditional smoke detectors. As the electronics within these smoke detectors analyze these output signals, and as these spikes repeatedly occur over a given period of time, the result is nuisance alarms.

Smoothing algorithms essentially act to dampen these surreptitious output spikes, enabling these specially designed detectors to discriminate between false and real smoke signatures. In addition to traditional drift compensation, maintenance alerts and other features, smoothing algorithm technology has the potential to significantly reduce nuisance alarms.

Multiple Sensors Aid Recognition
Another way to combat the nuisance alarm problem is to utilize more than one sensor technology in the same individual and system-type smoke detectors. The simultaneous monitoring of several sensor types enables the smoke detector to better determine whether smoke is being generated by a fire, burning toast or a room full of smokers.

This technology works by comparing the output of each sensor and comparing the composite sum to a standard model. This model is developed from actual data obtained during fire tests. It exists as a mathematical representation contained in microprocessor memory inside individual smoke detectors or the analog addressable head-end system they connect to.

This technique enables a smoke detection system or an individual detector to render a better decision as to whether there is a fire in the vicinity. The two common criteria used in this type of detection scheme are that of analog heat and smoke detection via airborne particulates.

“It has been shown that the best combination for early detection has been the complement of ionization, photoelectric, carbon monoxide and temperature,” said Walter W. Jones, a physicist with the National Institute of Standards and Technology (NIST), in a research paper entitled, “An Algorithm For Fast And Reliable Fire Detection.”

The detection of a fire using the multiple-criteria approach hinges on the use of several low-level sensors that have the ability to report analog information regarding specific conditions in the environment. By monitoring the ambient temperature, the rate of temperature rise and the presence of smoke particulates in the air, a more reliable method of detection can be derived.

“The information from the sensors themselves is analog data, measuring temperature, obscuration, species density, heat flux and other characteristics of the environment. What is needed is a means to use this information directly to provide earlier warning, and more specific information before and after alarm using these sensor suites,” he says.

Innovation Doesn’t Stop
No matter how good a job fire detection equipment manufacturers do, the work will never be entirely finished. As more sensor technologies and software options come to light, better and more reliable detection schemes will emerge. Fire technicians and security dealers must be poised to utilize them for the betterment of their clients.

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