In the first two chapters (Part 1 is here!, and Part 2 is here!) I have described fire detection systems combined with alarm systems. With this kind of system, humans have to take the final operation to confirm the danger and extinguish a fire. In this post, I will describe fire fighting systems that are operating without human action. This gives a much faster reaction and increases the possibilities to extinguish a fire on board. We can also reduce the amount of crew onboard.
Water mist – dry fire protection system
A water mist system is a fixed fire protection system that discharges water in a fine spray of very small water drops. The biggest advantage of this system, in my opinion, is limited damage to machinery. There are no chemicals in use and the system reacts fast. How does it work? The system is simple. It is built by a water tank with fresh water. The water pump will build pressure if the system needs to operate. Sensors, the best is 2 different kinds of the sensor. For example ignition detectors combined with the smoke detector. Then we are sure, there will be no false alarm which flood secured space with water. Of course, there can use different kinds of sensors, as a good example can be a camera with AI (Artificial Intelligence) software to detect flames. So system design can be quite different from project needs. However, we can point to some standard elements which will be in all different kinds of water mist systems. Look at the graphic below.
Main parts of the system are a freshwater tank, a pump to build up pressure in the system, a nozzle to spread water incorrect shape. 2 different types of sensors one gas and one heat detector. The activation of both sensors will release the alarm and start the pump. Water will be delivered to water mist nozzles which create an air-water spray to extinguish the fire.
Classic sprinkler – wet fire protection system
The water mist system is permanently dry. Water comes inside the piping only when the pump starts. But there is also a different solution. A permanently wet system, with water circulating in piping. There are very simple and efficient systems. Originally the systems have nozzle and sensor in one place. Between thread and deflector is build glass bulb with liquid. Depends on the place where it is installed can have a different temperature of working. For example, in-cabin 68 degrees Celcius will be enough to start acting but for washing room with drier inside more likely will be a solution with 100 degrees start.
In this simple system is one big minus. What happens if You accidentally hit the nozzle and the glass bulb will break? You will flood area, maybe unnecessary damage to some equipment. A much better solution is to have valves before each sprinkler. This solution can be combined with a standard fire system and create an alarm based on fire detectors, and depend on the operator can be directly started or manually released. So this solution gives us more flexibility and we can create hi risk areas with immediately taken action and less important areas which can be inspected first before the flood of the area. Risks and advantages always have to be taken to account.
You can find nice presentation about wet and dry systems here. Of course, if You are interested in more details, You can always comment or contact me via email.!