Fire Suppression. Water-Mist : A Revolutionary Green Technology in. - by Nimit Sheth TALL, SMART, SAFE BUILDINGS FOR SMART CITIES.

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2 Water-Mist : A Revolutionary Green Technology in Fire Suppression - by Nimit Sheth Introduction Water-Mist... A Revolutionary Green Technology in Fire Suppression is being researched for more than 50-years but only recently, it has being effectively used in various developed nations for various fire suppression needs, point-protection localised application in lieu of conventional fire-fighting system and total-flooding for suppression of fire. Only recently in India, many Fire Authorities, Government Dept., Municipal Corporations, Corporates etc. have understood the importance of Water-Mist in Fire Suppression and have implemented this technology as an effective and as a far better fire fighting system. It not only helps in reducing the latent heat, but also makes a layer of mist & supress fire and its possible re-ignition. The added advantage is it can be used in virtually all class of fire & especially in electric-fires, which is about 75%-80% the cause of fire. It s a Green Technology, whereby water needed in firefighting is reduced to more than 90% & it has 0-ODP, 0-GWP & 0-ATL. It s non toxic, self coolant and does not have any harmful effect on environment or humans. Following the restrictions imposed in the Montreal Protocol and Kyoto Protocol for the use of halons and other HCFC/HFCs based chemicals / gases which deplete 50 INAUGURAL ISSUE FSAI JOURNAL

3 the ozone layer & increase global warming, there has been a great deal of movement in the fire protection systems market, both nationally and internationally for its substitutes. New extinguishing agents have appeared and new norms for its usage & standards for its design have been created. Water mist is one of these sustainable new agents, which in recent years has demonstrated its effectiveness in protecting against fires without any damages to humans or environment. Water mist systems are suitable for the following risks: 1 Machine rooms (transformers, motors, turbines, etc). 2 Light Hazards and Ordinary Hazards 3 Deep-fat fryers 4 Cable tunnels 5 All Solid A Class fire & Specific B & C Class of Fires 6 Specialised Building / Premises / Application where collateral damage from water is much more. Fire protection systems with water mist are based on the atomisation of water to form very small water droplets, so increasing the contact surface area between water and air and therefore, increasing the transfer of heat by convection. Consequently, the effects of water are optimised and discharge of small amounts of water controls the growing fire and extinguishes it. It works at pressures between 80 and 200 bar and the nozzles / sprinklers are designed to enable water to be discharged as a fine mist at the above working pressures. The main advantages that Water- Mist Fire Protection Systems offers are: 1 Drastic reduction in temperature of the protected risk. 2 No heavy collateral damage as compared to water, as minimal water is used in mist form. 3 Easy to refill. 4 Ecological: environment friendly. Water Mist is one of the sustainable new extinguising agent, which in recent years has demonstrated its effectiveness in protecting against fires without any damage to humans or environment FSAI JOURNAL INAUGURAL ISSUE 51

4 5 Economic system refilling. 6 No decomposition products are generated. 7 Partial scrubbing of combustion fumes. 8 Covers larger area of fire & lesser space to install. 9 Lesser man power required to operate. 10 Low maintenance, easy and simple operation. 11 Is useful in electrical fires, combustion fires & liquid fires. Extinguishing Mechanisms When a small quantity of water is sprayed at high pressures to make very fine disjointed droplets of water, with an exponentially larger surface area, then the small water droplets rapidly evaporate at the fire source due to high temperature. Vaporization of water increases the water volume by times and the oxygen is displaced locally at the fire source. As a result, a localized inerting effect is generated at the fire source. When the water vapor (now in expanded form & much larger than its original size) starts to displace the oxygen from the fire, it leads to starvation of oxygen. Once this oxygen is completely depleted, the fire starts losing intensity and is extinguished. This also ensures that the fire does not re-ignite as the surroundings are being continuously cooled. There are different means by which water mist interacts with fires: By oxygen reduction: Reduced oxygen in the flame can be achieved by diluting oxygen in the entire enclosure where the risk is located or by a local reduction in oxygen within the flame. The first situation involves reducing the concentration of oxygen by up to 12-15% (depending on the temperature of the flame and the type of fuel) within the enclosure. The effect obtained is the same as with the inert gas system. Unlike inert agents that are in a gaseous state at room temperature, water mist system which progresses to the vapour stage depends on the energy released by the flame. Inerting is achieved by creating conditions of 100% relative humidity at temperatures of between 60-85ºC. In the second situation, the droplets that evaporate inside the flame displace the oxygen locally by occupying times its volume. By absorbing the heat of the flame: Cooling the flame extinguishes the fire. For water, the energy is absorbed through evaporation (from a liquid to a vapour state) with an amount of heat equivalent to 540 calories per gram being absorbed. The water that does not evaporate, therefore, participates in extinguishing. The increased calorific capacity of air with water vapour should be added to cooling through water evaporation, which allows the flame to cool (the temperature of the flame depends on the heat released by the combustion reaction and on the calorific capacity of the compounds present). Cooling of the risk: One of the advantages of water mist systems is the capacity to cool the risk. When the water mist system is activated, the temperature of the 52 INAUGURAL ISSUE FSAI JOURNAL

5 System type Water storage Nozzle type Detection Installation type Cylinder Pump Cylinders Tank Open Closed With thermal Independent banks unit bulb detectors Total flooding x x x x x x Wet Pipes x x x x Pre-action x x x x x x x risk cools rapidly, so minimising re-ignitions and offering a safer environment for fire-fighting personnel. Radiation attenuation: Water mist systems also have a huge capacity to attenuate radiation released by flames and stops the fire from spreading to other areas. Type of application Total Flooding Systems (Deluge systems): These systems maintain the pipe network without pressure in normal conditions. Discharge starts when the system is activated. Fire detection is independent from the extinguishing system and it is the detection system which triggers the water mist system. Wet Pipe Systems: These systems maintain water pressure in the pipe grid (7 to 30 bar) in normal working conditions. The heads connected to the system include a fire pump, which when activated, discharges the pressurised water through sprinkler in the defined area making a fine mist. The fall in pressure in the grid activates the pumps through pressure switch and discharge occurs in the activated heads. Required pressure in the grid is maintained through pressurization pump. For emergency purpose, in case of mains power failure, DG driven pump can also be installed as a back-up. Pre-action Systems: These systems maintain the discharge grid without pressure and use closed atomiser heads and complementary detection. If the fire is detected, the system is activated loading the water pipes, but it will only discharge in the atomisers whose bulb has broken due to thermal effects. How the system works: 1 Automatic activation through the detection of low pressure in the systems that work with the pressurised installation by means of the auxiliary pump. The system s pressure is controlled, which, when it detects a fall in the pressure below defined limit due to possible micro-leaks, the control panel sends the signal to the Jockey pump to re-establish the pipe pressure to pre-set bar. If one of the bulbs in the atomiser heads bursts or main system fire-fighting has operanalized, the Jockey pump is unable to supply the necessary water flow to maintain the pressure. In this case the control panel will send the activation signal to the main pump (the jockey pump is deactivated at this point). In case of power failure of mains, if the DG driven Water-Mist Pump is installed, then DG pumps would have to start manually, Water mist systems have a huge capacity to attenuate radiation released by flames and stops the fire from spreading to other areas FSAI JOURNAL INAUGURAL ISSUE 53

6 with low, intermediate or high pressure system with droplet sizes from & pressure as low as 7-30 kg for nozzle / sprinkler to kg for fire-fighting / total flooding. These systems with its variant droplet size distributions, flux density & spray dynamics are being designed based on various research & long usage of systems with trial & errors and it is continuously upgraded as per challenges sought by concerned authority. 2 For non-pressurised installations, the auxiliary pump can be started automatically instead of maintaining pressure in the installation. When a fire is detected by detectors, the fire alarm panel through its module and built-in atomization will activate the main pumps. The main pumps will remain on until the command is given to stop the system manually or the system detects the minimum level in the deposits / media. When the system comprises more than one main pump, once the first pump has started, if, within a certain period of time it does not provide sufficient flow, the PLC automatically starts up the second pump in the pressure unit sequentially to avoid excessive peaks in the mains power supply current. 3 Manual activation from the electrical switches in the electrical control panel which ensure that the pumps can be started up even though everything is malfunctioning except, logically, the mains power supply. Standards & Norms: The NFPA 750 defines three pressure regions for water mistgenerating technologies: low, intermediate and high pressure systems. Though various standard & norms including NFPA-50 have been in place for Water-Mist, but various researches across the world are still being done to make this technology even better, most cost effective and user friendly with proper effectiveness in different circumstances and in conflict with different combustion materials in case of fire. Water-Mist technology is being effectively developed by various companies, scientific bodies, fire authorities, research institutes etc. as per their local challenges and optimum requirement. Its developed Conclusion The technology of fire-suppression since ages has been evolving & after lots of damage to our Mother Earth through harmful chemicals, we shall be back to basics & most of the fire would be extinguished with its natural media water, with its minimal usage & minimal damage to man/ machine during its operation. Though this system has been in focus for more than 50-years & various researches have been carried out of its utility and capability of effective fire fighting agent, but still lots need to be done to make this technology acceptable in each form of extinguishing technology & media. With more research and much more of its usage, this technology would be available at very low cost and with its wide usage and acceptability, most of the fire would be extinguished with Water through Water-Mist Technology a very natural resource of the universe. Even the quantum of water will substantially decrease whereby, preservation of water would take place and its excess wastage or unnecessary storing of huge quantum of water would not be required. Mr. Nimit Sheth is President Fire & Security Association of India (Gujarat Chapter) & MD of Ramana Safety & Systems (I) Pvt. Ltd., an Ahmedabad based company. He is into business of life safety providing solutions, services, systems from conceptualization, design to commissioning in the field of fire protection system, security surveillance systems, low voltage system (ELV) & IBMS since more than a decade now. He is Life Member of Fire & Security Association of India (FSAI) & Associated Member of National Fire Protection Association (NFPA), National Safety Council (NSC) & Gujarat Safety Council (GSC). nsheth@ramanasafety.org 54 INAUGURAL ISSUE FSAI JOURNAL