Fire protection systems onboard pt.1

For the units at sea, there are different risks, which can damage the vessel. Except for unfriendly environmental, water, there is another. Even more common reasons for accidents onboard are fire accidents. Why fire is so dangerous if we have o lot of water around? We have an unlimited amount of saltwater around the vessel. This is true, but the case is to do not flood the vessel. This is always possible, then the fire will be gone. The main challenge is to rescue the crew to a safe place and continue extinguishing operations. Which is not so easy in the middle of the ocean. The system has to prevent and detect every potential danger. Systems have to eliminate fire as fast as possible. This is the responsibility of the Fire protection system onboard: detect, and extinguish the fire.

Fire protection system – How does it work?

Fast response and reliable system is a key to protect vessels from fire. To describe how the complete system is working, You have to know first, how different sensors are acting. The most important part of the fire protection systems is the sensors. They are responsible for the detection of danger. There are a couple of different types of sensors to detect threats. Better sensors we have, faster and more accurate reactions crew can make onboard.

3 types of most common use sensors in fire protection systems are smoke detectors, heat detectors, and ignition detectors. There are 2 different types of smoke detectors sensors. Optical smoke detectors or smoke detectors with radioactive material. Heat sensors are usually equipped with thermistors. Ignition detectors are working with photocell.

Optical and ionization smoke detectors in Fire Protection Systems

Smoke sensors in detection

You can see in graphic 1, above, the optical smoke detector is built of 3 main parts. 1st a light-emitting diode which is emitting light, 2nd Photocell which is detecting light emitted by a diode and sends an electronic impulse to the 3rd part, the microcontroller. If smoke is going inside the casing of the detector, the photocell is not detecting light, so the microcontroller has an alarm signal from the photocell. Simple as that.

The cheaper solution, not so environmentally friendly, but still very common is ionization smoke detectors. This kind of detector has also 3 elements. 1st are electrodes. 2nd is an ionization chamber build between electrodes, which contains the small chemical element americium. Free electrons and ions of americium between electrodes are moving that long, how the air inside the chamber remains clean. When smoke is going inside, then the current flow between electrodes is stopped, and the signal is detected in the 3rd microcontroller.

Both types of smoke detection sensors can detect fire multiple times. You don’t have to replace them after one use. After the extinguished fire, smoke will go away. When the photocell is detecting led light again and electrons of americium can move again. Sensors are ready to operation again.

Heat and Ignition detectors in Fire Protection System

Heat and ignition detectors in Fire Protection System Onboard

In graphic 2, You can see heat detectors are very simple. This type of sensor has only 2 components. Thermistor and electronic board. When the temperature increases, the thermistor change resistance. After that, the alarm gets active. The last type of sensor is the ignition detection sensor which is simply a photocell sensor. When photocell detects the flame, the alarm gets active. To fulfill all elements of the system, we can found also manual call points, to release alarm by hand operation.

Now You know what kind of signals release fire alarms. In the next chapter, You will learn, how the fire protection system is designed. We will start with this topic in the 2nd chapter about the fire protection system.


  • Mateusz Białas

    Researcher of Autonomous and Remotely Controlled ships. Since 2014 in Maritime Industry. Experience gained at Ro-Ro, Ferry, Container, and Heavy Lifts, design of Navy Ships.

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[…] These are the two most common proximity sensors used onboard. However, You can found also optical proximity switch. With using the photocell. However, the most popular optical sensors with infrared. They are basically photodetectors, which detect reflections nearby. A good example is smoke detectors with photoelectric cells. I already describe them on the occasion of fire protection systems. Here you can find the post. […]


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