Scattered for Safety - Diffused Light Prevents Danger

Silent Killers

In 2019, approximately 90% of the fire related deaths and injuries in the U.S. occurred in homes or apartments . There are no official statistics for the EU but estimates of the European Fire Safety Alliance show similar rates at approximately 80%.  In those cases, most people do not die from the flames, but from the smoke. Depending on the burning materials and on the amount of heat generated by the fire, smoke consists of different gases. All of them are dangerous, but in different ways.

The most frequent and deadly components are the so-called “toxic” gases, which include carbon monoxide (CO), carbon dioxide (CO₂), and even hydrogen cyanide (HCN). They affect respiration in different ways: Carbon dioxide is commonly known as the “waste product” of respiration that is released when we exhale. The problem is that the whole metabolism gets out of balance when the CO₂ concentration increases. If the air you inhale contains more than 10% CO₂, you will be dead in less than a minute.

Carbon monoxide is just as lethal, but in a different way. Its molecules attach themselves to the hemoglobin in the human blood, which is there to transport oxygen to the cells. As an effect, the cells do not get enough oxygen to function causing the body to suffocate. The most dangerous fact about CO is that it does not have a smell or taste. Cyanide causes breathing difficulties very rapidly when it is inhaled or absorbed through the skin. Like CO it also affects the metabolism, but on a different level, prohibiting energy production within the cells. Actually, most victims suffocate in their sleep before they even notice the fire.

This is, where smoke detectors kick in. As soon as they detect a potentially dangerous amount of smoke, they set off an alarm and make sure that the inhabitants wake up.

IR-Detection Saves Lives

In most cases, smoke detectors use optical technologies. The concept is as simple as it is effective: It consists of a light source, some small mirrors, and a photodiode. The mirrors guide a light beam through a dark box and make sure that it never hits the detector. As soon as smoke enters the box, the light is scattered and reaches the photodiode, which then triggers the alarm. However, there has to be some type of margin: You do not want the alarm to go off with every candle you light. On the other hand, it should be triggered when said candle falls to the floor and sets the carpet on fire.

Home applications use a simple IR emitter and an off-the-shelf photodiode, while the more expensive industrial applications employ the more sensitive combination of a brighter (laser) light source and a more “professional” photodiode.

Whether in the home or in a business, all smoke detectors require smoke to physically reach the detector. Valuable time passes on the way there, and the direction of movement of the smoke depends on numerous external factors. A small gust of wind can have a profound effect on the direction of the smoke. Optical flame detectors, on the other hand, do not require contact: they work quickly and from a distance. Their IR sensors react to the flickering of flames or sparks. An algorithm analyzes whether they correspond to patterns that occur during fires. For example, they are also able to detect sparks through windowpanes, billows of smoke, and dense fog.

Spark detection is particularly important where explosive dust floats in the air (e.g., in wood processing, grain processing, and cement plants). The key here is to react quickly and, if possible, extinguish the sparks while they are still in flight to prevent any further damage. Quantum detectors (PbS, x-InGaAs) dominate these sensors.

Another industrial application is flame detection. In this environment, many fires originate from the combustion of hydrocarbon compounds. Such fires often spread farther than the visible flames would suggest. Pyroelectric detectors can be used to determine their true extent. This sensing technology detects the products of combustion, such as CO₂, by measuring light emissions at specific wavelengths. At hot temperatures, gases emit the same wavelength of light that they otherwise absorb. This makes it possible to clearly determine the type of gas in the detector’s field of view. Pyroelectric detectors are always used in combination with infrared filters that block out the “ambient noise” generated by solar radiation or by atmospheric CO₂. For multispectral detection of IR radiation from flames, a multiple combination of three or more detector/filter pairs is usually used.

All of these systems operate quickly and with extreme precision because in industry you cannot afford false alarms. If sprinkler systems or other extinguishing systems are triggered incorrectly even once, the consequences can be just as devastating as a fire.

Intelligent Solutions Go One Step Further

Standard solutions have thus far included combining the smoke detector with either a heat sensor or a carbon monoxide sensor. DEF, a French solutions and services provider of fire safety systems, recently developed an intelligent, connected device that combines all three of these technologies for the first time. Most standardized multi-sensor detectors combine smoke detectors with either heat or carbon monoxide. The premium version of this solution is self-learning: It uses built-in algorithms to process the signals from the various sensor technologies. For this purpose, they record and analyze the alarm context and the last 100 events. In this way, they can determine the type of fire and thus adapt their sensitivity to allow for earlier detection but also reduce the number of false alarms.

While the first of these multi-functionality devices were designed as premium products for factories and shopping malls, they are already on their way to the common living room. As part of a smart home, they could be controlled with any type of mobile device and allow you to react to dangerous situations, when you are miles away … assuming you have access to a high-performance data network.