Smoke detector - more interesting than you think

Message from: 23-01-2024

A Few Words of Introduction

In 2021, the State Fire Service recorded nearly 39 thousand building fires, of which over 85% were residential properties. This statistic is not encouraging, which is why it is so important to raise awareness that we can minimize these numbers and, above all, reduce the losses that result from fires. What immediately comes to mind - and rightly so - are smoke detectors. They allow the fire service to respond quickly and then control the threat before it escalates. The topic becomes particularly relevant during the heating season. During this period, the risk of fires increases significantly, putting our homes and ourselves in great danger.

Faulty electrical installations, devices, or atmospheric discharges are also fire hazards that occur year-round, which is why it is 100% true that the best time to purchase a smoke detector is now.

This useful device in every household works in an obvious way - it signals the presence of smoke in the room. However, electronics do not possess a natural sense of smell, so it must detect smoke in some way. How does this happen? How did it work in the past, and how does it work now? Are there different methods of smoke detection? We take on the challenge of answering all these questions.

Detector or Sensor?

According to industry standards, a detector refers to a ready-made device that can operate independently or be integrated into a whole system, such as an alarm system. A sensor, on the other hand, is a specific element inside that device, sensitive to a given stimulus, such as a pyroelement - a motion sensor in a motion detector. This is how it looks from the perspective of professional terminology, but in everyday use, both words are often used interchangeably to refer to the same thing - a ready product. Nevertheless, this may be interesting information for the uninitiated, and in some cases, it can help avoid misunderstandings. Now we know that if one detector has two sensors, we may be dealing with a specific device, not an editorial error.

A Brief History of Detectors (and Sensors!)

The history of smoke detectors dates back to the early 20th century and is a journey full of innovations and improvements. The first concepts emerged over 100 years ago, including George Darby's "Electric Heat Detector" from 1902. In the 1940s, ionization detectors were introduced (more on that shortly), and in the 1960s, photoelectric detectors. The 1970s brought combined detectors that integrated both technologies. By the late 20th century, detectors became more reliable and accessible, and the development of legal regulations and safety standards contributed to their widespread use. In the 21st century, smart smoke detectors emerged, integrating with smart home systems.

How Does It Work?

As you can see, history has revealed many different technologies that are used in the design of devices. Many of them are still present on the market today. The most commonly encountered solutions are photoelectric detectors, which use light scattering on smoke particles, and ionization detectors, which rely on air ionization through radiation. Photoelectric detectors work by detecting radiation reflected from smoke particles, while ionization detectors respond to changes in current intensity caused by the presence of smoke. There are also models that combine both technologies.

Smoke Detectors with Optical Detection

It turns out that the mechanism of action of optical detectors is really simple - and perhaps because of this, effective, as it is widely used in the most popular devices. Inside the round housing of the detector, there is a chamber with a light source (usually an LED). The second essential element is a photoresistor. This is a light-sensitive element - it changes its electrical resistance depending on the intensity of the light that falls on it. It might seem that the resistor receives a signal from the diode, and when smoke comes in the way, the intensity of the received signal decreases. The fact is that it is… literally the other way around! The diode and photoresistor are not connected in a straight line - they are placed in the chamber in such a way that under normal conditions, the light from the diode does not reach the receiver (Fig. 1).

However, when smoke enters the chamber, its particles act as a scattering medium - the light scatters on them and can overcome that one crucial bend necessary for the light to reach the photoresistor (Fig. 2). The same phenomenon occurs when driving a car at night in fog. You can notice that the light scatters in all directions, and when it is very strong, it can even slightly blind us. And now we have an alarm situation. The detector can emit an alarm signal by itself or send a signal to the entire fire system, where the control center will take appropriate action - notifying the fire department and the property owner. It is worth noting that a smoke detector can react just as much to dense water vapor generated by e-cigarettes.

Fig.1

Fig.2

Isotopic Ionization Detector

Ionization detectors use heavy radioactive elements, which provide them with high sensitivity to detecting fire smoke. They are characterized by greater effectiveness and fewer false alarms compared to other types of detectors. Nevertheless, like other smoke detectors, they require regular inspections according to legal regulations. We also do not need to worry about the presence of radiation - its intensity is so low that the devices are 100% safe for health.

The construction of ionization sensors makes them resistant to changing external conditions. Ionization of the air occurs due to alpha particles emitted from a radioactive source. The device consists of two chambers - one open to the outside and the other closed. Collisions of oxygen and nitrogen particles lead to the formation of ions, which causes the flow of charges and the creation of current. In the event of a fire, smoke entering the open chamber disrupts the current balance, which is detected by the measuring system, and consequently activates the alarm. The second, closed chamber plays an important role, serving as a reference against which we compare the state of the open chamber exposed to smoke. This ensures greater detection precision and resistance to weather conditions.

Which Smoke Detector to Choose?

Optical or ionization sensor? Solutions based on radiation phenomena are usually more effective when it comes to detecting what is invisible, such as combustion products other than dense smoke. The optical detector, on the other hand, will respond the fastest to the appearance of dense smoke - exactly what the human eye can see. Both technologies are continuously being developed, so it may have once been confidently stated that ionization detectors were the only truly professional solution, but now that would be an exaggeration. Some manufacturers combine both technologies in their top products, additionally enriching the device with the detection of a third factor - temperature, which, as we know, is higher than usual during a fire. Such 3-in-1 solutions are the best if we care about maximum effectiveness.

That’s not all. The market offers many models of smoke detectors that look the same at first glance. Therefore, when choosing a smoke detector, special attention should be paid to the parameters - both of the room and the device, as they will determine whether a given smoke detector will work in your space:

Ambient temperature - matters when we intend to install the detector in places with elevated temperatures, such as in the kitchen.
Humidity - just like with temperature, attention should be paid to the humidity present in the target room. There are models available on the market designed for elevated humidity levels.
Power supply type - most detectors have a battery slot, but there are also models powered centrally.
Sound signal intensity - production halls with heavy machinery, cinemas, etc., are places where it is advisable to choose detectors with a louder alarm than the standard 80db.

It is important to remember that choosing the right equipment and its configuration is one thing. Equally important is the proper placement of detectors - it is always worth, or rather necessary, to familiarize oneself with the manufacturer's recommendations or to have the appropriate layout planned by professionals. According to research by the UK government (The Home Office collects detailed information on incidents attended by Fire and Rescue Services), the cause of about half of the cases of alarm system failure was that smoke did not reach the detector. The sight of detectors in the middle of the ceiling in a room is not accidental, although it is always worth approaching the topic individually.

Think Holistically

We always say that safety should be approached by considering all possible threats. Smoke detectors are just one element of the whole, and when planning to equip an apartment, house, or office with appropriate devices, it is worth planning the entire system right away. After all, many fire protection solutions can be integrated with our alarm system, to which various types of detectors are connected. We wouldn’t be ourselves if we didn’t add that the crowning of a well-prepared alarm system is appropriately selected video monitoring. We assume that the most important things are kept in a safe that is resistant to both fire and burglars.

Holistic approach wins! And when we also know how it all really works, we can feel even safer. You already know quite a bit about smoke detectors.