1 Introduction

Fire existed even before people learned to use it for personal needs. With civilization development, it became an integral part of life, and more ways of using fire emerged out. Efficient and diverse use of fire outset the risk and hazards associated with it. Worldwide uncontrolled fire accounted for the huge loss of property and human life. Increasing fire disasters caught attention of different countries and led to manifestation of fire protection measures and utilization of new fire extinguishing technologies. The fire protection industry has always been looking for the development of a fire suppression method/technology that can address all classes of fire and does not make any negative impact on the environment.

In 1940’s Halon emerged as one of the most efficient fire extinguishing chemical/technology and gained worldwide attention. But later on, it was phased out in accordance with Montreal protocol-1987 because of the formation of HF and HBr having high potential of depleting ozone layer [1]. Subsequently, the ban on Halon fire extinguishing technology triggered the research on development of Halon alternatives all around the world. Many Halon alternative fire extinguishing technologies such as Novec 1230, foam, hydro fluoro carbons (HFCs), dry powders, inert gases, water mist, carbon dioxide, aerosols etc. emerged out [2,3,4,5,6,7].

Water mist fire suppression technology pumps water with high pressures through nozzles and forms ultra-fine droplets of water to extinguish fire. But it has several drawbacks such requirement of high-pressure cylinders, high fire extinguishing time, high potential for damaging electrical equipment, high maintenance cost etc. Carbon dioxide is widely used for extinguishing fires, but it displaces the oxygen in the affected area and due to its acidic nature, it also causes leakages in its system. Halocarbon fire suppressing agents such as FM 200 and Novec 1230 extinguish fire by physical and chemical mechanism but at high temperatures, they decompose to produce hydrogen fluoride, which is highly toxic and corrosive. Inert gases are also effective fire extinguishing agent, but these are stored at high pressures (around 300 bar), which causes storage and maintenance problems [8].

Condensed aerosol-based fire extinguishing system (CAFES) has come up as the most promising halon alternative. CAFES (described in detail in further sections) produces hot aerosols when pyrotechnic based aerosol forming composite is ignited using electrical or thermal igniters. Thus, produced hot aerosols are cooled using cooling pellets arranged within the CAFES. Aerosols extinguishes fire via physical and chemical mechanism (inhibition of chain reaction of fire propagating radicals) [9]. It has a large number of advantages as compared to other alternatives, Fig. 1. CAFES possess zero ozone depletion potential (ODP), negligible global warming potential (GWP) and atmospheric lifetime (ALT) [10]. The CAFES technology is considered environmentally safe with respect to ODP. However, the release of carbon dioxide and micron size aerosol particles contributes to GWP and ALT. CAFES have flexible, compact, and modular structure, all that makes it weight and space saver with simple installation protocols. It can be fixed/installed in small spaces unlike other fire extinguishing technologies which require high pressurized cylinders and large piping network for driving out the agents. It is highly effective against multiple classes of fire (A, B, C & F), cost effective and has high durability. CAFES also have some disadvantages such as reduction in visibility due to light scattering by aerosols, chances of secondary fire because of high temperature of aerosols, corrosion to electronic equipment because of hygroscopic residue, cleaning issues due to aerosols settling and production of some toxic gases along with aerosols. Efforts have been made by researchers to tackle the disadvantages to the best possible extents by modifications in composites producing and cooling the aerosols.

Figure 1
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Advantages and disadvantages of condensed aerosol-based fire extinguishing system

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Over the last decades, there are several companies/industries worldwide which are involved in manufacturing and supplying of condensed aerosol based fire extinguishing systems [11,12,13,14,15,16,17,18,19,20,21,22,23] and have found versatile fire protection applications, Fig. 2. This technology is very effective in extinguishing class B fires in machinery spaces, gas turbine enclosures, engine compartments, fuel storage areas, energy storage systems [24]. CAFES have been employed for the protection of heritage properties, archives, storage rooms, accommodation spaces, libraries etc., which are the sources of class A fire. It has also been found promising in extinguishment of electrical fires, hence protecting electrical substations, electrical panels, control rooms, UPS rooms, computer, and electronic equipment [25]. These electronic units are heart of several industries and companies, so this technology has marked its footprint in various industries such as mining, oil and gas, power generating plants, chemical industries etc. This technology is also protecting the transportation and locomotives vehicles such as cars, trains, buses, ploughing trucks, yachts, ships, scooters etc. [26].

Figure 2
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Real time applications of condensed aerosol-based fire extinguishing system

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Literature clearly indicates that condensed aerosol based fire extinguishing systems have found fast growing implementations and versatile fire safety applications. Considering this, efforts have been made in the current review to pile up the recent developments and applications of condensed aerosol-based fire extinguishing systems worldwide. The progress that has been made over the last few years for its improvement has also been brought out. Since there is no organized compilation of application of CAFES available up to date, it is an essential area to be reviewed and tabulated to attract the attention of fire technologists, and also impart application knowledge for future implementation of fire efficient technologies.

1.1 Condensed Aerosol-based Fire Extinguishing Systems (CAFES)

Condensed aerosol-based fire extinguishing system is one of the most efficient fire suppressing technology that has been introduced to the fire protection market since 1990s. This technology emerged from Soyuz rocket program in Soviet Union, Russia [27]. Aerosol forming composite (AFC) is an essential component of condensed aerosol-based fire extinguishing system and is generally comprised of pyrotechnic composition. A pyrotechnic aerosol composition generally consists of a mixture of an oxidizer which is the sources of oxygen, fuel that combines with the oxygen for combustion and a binder to hold all the ingredient together to provide strength to the composite. Oxidizer is an inorganic salt, such as nitrates and perchlorates of mostly sodium, potassium, and strontium. Fuel or combustible binder is generally metal powders and/or organic polymers such as aluminum, magnesium and/or phenolic resin, epoxy resins, respectively.

When aerosol forming composite is ignited, thermally or electrically, oxidizer reacts with the fuel cum binder and generates carbonates, bicarbonates, chlorides of respective oxidizer salt [28]. Thus, produced hot aerosols are cooled to acceptable limits using cooling pellet composite (CPC) arranged within the CAFES. Therefore, CAFES is comprised of igniters, AFC, CPC, spacers, etc., all assembled within the casing of CAFES, Fig. 3. During application on class A or B fire, aerosols interact with flame and generate metal radicals. These metal radicals then quench the fire supporting radicals (H*, OH* & O*) forming stable compounds (KOH, H2O etc.), and thereby extinguishing the fire, Fig. 4.

Figure 3
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Casing of condensed aerosol-based fire extinguishing system

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Figure 4
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Fire extinguishing mechanism of condensed aerosol-based fire extinguishing system

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The efficiency of condensed aerosol based fire extinguishing system is determined with various parameters such as percent discharge, burn rate, minimum fire extinguishing concentration, ignition temperature, shelf life etc. Several countries like Russia, China, Europe, USA have developed their own standards such as ISO 15,779, IMO-MSC/Circ.1007, BRL-K23001/03, NFPA-2010, UL-2775, GA 499.1 (2004–2010) etc. for test and evaluation of CAFES in different fire scenarios [29]. According to UL-2775, % discharge must be ≥ 90%, fire must be extinguished in 30 s for a 100 m3 chamber. United States Environmental Protection Agency (US-EPA) has approved aerosol based fire extinguishing systems for un-occupied or normally not occupied areas under its significant new alternatives program (SNAP). And more recently, the system has been approved for occupied areas (powdered aerosol D, STAT-X, USA) [30]. Approved or listed CAFES have been extensively used for fire protection in various fields such as power generation, energy storage systems, heavy industries, storage rooms, commercial buildings, marine, defence, manufacturing tools, transportation etc. Several case studies and test & evaluation reports, indicating the applicability/utility of CAFES for fire protection of particular enclosure/system are available in open literature and compiled herein.

2 Real Time Applications of Condensed Aerosol-based Fire Extinguishing Systems

2.1 Energy Storage Systems

Nowadays, lithium ion batteries are extensively used as a power source in electrical vehicles, hybrid electrical vehicles, aerospace, mobile phones and laptops [31]. Lithium ion batteries are generally composed of an anode, cathode, electrolyte, and a separator. It combines high energy materials such as separators made of polymers & resins (Class A fire) and highly flammable electrolytes such as ethylene carbonates (Class B fires) [32]. Mechanical damage, short circuit, leakage or overheating of electrolyte, thermal run away etc. are the main causes of fire in these batteries [33]. Because of this thermal runaway, flames reach extremely high temperature and causes uncontrollable spread of fire. Thus, for suppression of lithium battery fire, the key factor is the cooling ability of the fire extinguishing agent. All water based fire extinguishants are efficient in extinguishing the lithium battery fires due to the cooling as their primary fire suppressing mechanism. Other agents such as dry powders and aerosols are also effective in extinguishing fire due to their fire radical quenching as primary and cooling as secondary fire extinguishing mechanism. During thermal runaway, cooling is must to avoid the explosion. For the cables and electronic parts of the battery systems CAFES can be an efficient fire extinguishants. Therefore, CAFES may be the associative tool for fire extinguishment of lithium battery fires. Several tests have been performed to test the efficiency of different fire extinguishing agents in extinguishing lithium battery fires.

Federal aviation administration (FAA), National Fire Protection Association (NFPA), and Civil Aviation Authority (CAA) carried out several experiments for extinguishing lithium battery fires [34]. Water based extinguishants such as AF-31, AF-21, A-B-D, non water based such as FM-200, FE-36, Halotron 1, powder extinguishing agent, purple-K, and Novec 1230 were compared with Halon 1211. For the experiments, an 18,650-lithium ion battery with 2600mAh battery capacity and 50% SOC was used. The battery was heated and then the fire extinguishing agents were sprayed. The results showed that only the water based extinguishing agents were able to inhibit the spread of fire and non-water based agents had no effect on lithium ion battery ions.

Many fire extinguishing agents were tested by Wuhan Institute of China Classification Society to put out the lithium ion battery fires [35]. The institute conducted an experiment to test the effectiveness of carbon dioxide, dry powder and heptafloropropane extinguishing agents. The efficacy of all the extinguishing agents was judged by various factors such as fire extinguishing time, rate of recrudescence and effect of smoke. Carbon dioxide and dry powder agents were not able to extinguish the fire and resurgence of fire was observed, and best effect was shown in case of heptafloropropane. Tianjin Fire Station of Ministry of Public Security also carried out the experiments for extinguishing lithium ion battery fire with dry powder, carbon dioxide, aqueous film forming foam (AFFF) and water mist technology [36]. The results showed that the carbon dioxide, dry powder, 3% AFFF could not extinguish the fire completely and resurgence of fire was observed with continuous release of heat and gases. Water mist fire extinguishing technology was also inefficient in suppression of lithium ion battery fires.

To test the efficiency of condensed aerosol-based fire extinguishing agent, an investigation was carried out by Robert G.C. Reijns to ascertain the suitability of aerosol extinguishing agent for extinguishing the lithium ion battery fire [37], Table 2. The test was conducted in Netherland, Europe in presence of certification authority (KIWA) and all the suppliers. The test was performed in a 40 feet container for 1.9 kWh fire using cleantron battery. To create a realistic test environment and to observe any adverse effect to the surroundings, several objects such as cradles, round and square bins were placed within the container. Smoke detectors were installed at the ceiling of the container according to the NEN2535 standard. At the rear end of the container’s ceiling, aerosol generators (CAFES) were positioned. As per fire test results, CAFES effectively suppressed the lithium ion battery fire and controlled re-ignition for at least 30 min with 61 g/m3aerosol density. Results hold good; however, the technology needs to be compared with other extinguishants having cooling as fire extinguishing mechanism.

A consolidated Edison BESS testing extension project was done by DNV GL in March 2017 for testing of CAFES for lithium ion batteries [38]. A battery abuse chamber was designed to hold the battery cells, thermocouples and FTIR gas analyzing probes deployed at multiple locations within the chamber. System was positioned in the lower corner of the chamber. For the test, batteries were charged to 75–90% of state of charge. To simulate the burning of the batteries, a thermal abuse mechanism was used by heating the batteries using heat lamps until failure reached. Aerosol extinguishing system was deployed, and a successful suppression of the fire was observed with no flashes or flames afterwards. Due to its light weight, compact, reliable, effective, easily installable, and low maintenances requirements, CAFES have been installed as fire suppression system in large number of companies having lithium ion battery storage areas that have been further indicated in Table 1.

Table 1 Application of Condensed Aerosol-Based Fire Extinguishing System in Energy Storage Systems
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M/s Bloomberg L.P. (media company, New York) replaced water mist fire suppression systems with aerosol fire suppression systems in the diesel generator rooms and battery rooms [39]. M/s Kokam Corporation, a leading rechargeable battery designing and manufacturing company in Asia, produces power conversion and energy storage systems enclosed in 40-foot mobile containers [39]. Samsung SDI, leading manufactures of lithium ion batteries produces energy storage systems enclosed in inter modal containers [39]. Since these energy storage systems are not much airtight so gaseous systems are not deployed, and due to compactness of these systems bulky fire extinguishing agents (pressurized cylinders) cannot be installed in it. Therefore, both implemented aerosol fire extinguishing systems for fire protection. Used and discarded batteries processing center, Van Peperzeel, located in Netherlands, transports the processed lithium ion batteries throughout Europe in inter modal containers [39]. Aerosol total flooding fire detection and suppression systems were installed in the PCS and ESS in containers. TU Delft University of Technology has a special energy storage system container for lithium ion batteries. On the basis of KIWA guidelines and protocols, aerosol suppression units were installed [39]. CAFES have also been installed in the engine bay of electric solar vehicle in Asia in Electric Solar Vehicle Championship (ESVC) [39]. Literature clearly indicated the successful installation of CAFES in protecting battery areas, however, the technology needs to be compared vis-à-vis water based cooling extinguishants. CAFES can be applied as an addon to cooling fire extinguishing systems.

2.2 Transportation

All over the world, the common transportation vehicles include buses, cars, trucks, trains, locomotives etc. Accidental fire in these vehicles generally originate from the engine compartment due to bursting of diesel tube, overheating of engine parts, oil/fuel leaks, electrical short-circuits etc. [40]. Fire protection of the engine compartment is essential as any type of fire can have devastating consequences to the vehicle as well as human lives. Since the engine compartment of these vehicles are generally compactly packaged and small in size, so a fire extinguishing system which can easily fit in it is needed. Condensed aerosol based fire extinguishing systems application for engine compartments of transport vehicles have been shown in Table 2.

Table 2 Application of Condensed Aerosol-Based Fire Extinguishing System in Transportation
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Pyrogen Corporation Sdn, Bhd Malaysia with Hong Kong bus service company assessed the efficiency of aerosol fire suppression system in bus engine compartment in the year 2000 [41]. The test was performed in a 2.064 m3 engine compartment (2.15 m × 1.2 m × 0.8 m) present at the double decker bus of Hong Kong city bus company. Aerosol generators used were one (100 g) and two (200 g). One 100 g generator was positioned at top right with the face of the nozzle towards the bottom left of engine, first 200 g generator was mounted at right side of the compartment facing cooling fan and the second 200 g aerosol generator was installed at back of the compartment facing towards right side of the compartment. Engine was run for 30 min before the fire test. A cloth was dipped in diesel and placed in the engine block and the surrounding areas. The fire was ignited, and one min preburn time was given, and thereafter the engine compartment door was closed. After two min of aerosol discharge, engine compartment was opened and investigated. The results showed the diesel fire extinguishment within 2/3 s.

Helsinki buses, a major bus operator in Finland has several hundred of buses [42]. Most of the buses are generally occupied with water mist fire extinguishing systems, but they demand time consuming maintenance and are not very efficient. After many testings and considering Swedish bus approvals SBF 128:1, aerosol fire suppression systems were decided to be installed in all the buses of Finland. The aerosol generators were directed towards the ventilation fan in the 4 m3 engine compartment with 123 °C as activation temperature for aerosol system [43]. Aerosol fire suppression systems have been installed in many school buses of USA [43], Georgia [43], South Carolina [43] to protect the front engine bay. Tests were performed in Singapore and Sweden buses using one 500 g and two 250 g aerosol systems respectively, and the bus fire extinguished successfully [43].

Eurostar International, a high-speed train service connects London and Kent in United Kingdom to the Paris and Belgium in France [43]. In order to provide fire safety to the train various systems such as water mist, FM 200, Novec 1230, inert gases and condensed aerosol-based fire extinguishing agents were researched as possible halon alternatives. The effectiveness of aerosol based systems was tested and approved by the Channel Tunnel Safety Authority (CTSA) and Channel Tunnel Inter-Governmental Commission (ICG) for control rooms, transformer, common block, motor block etc. In another example, power distribution area of a high-speed train namely Avelia liberty high speed train connecting Boston, New York city and Washington DC will be using aerosol systems [43]. These 28 new power cars will be running in 2021.

Aerosol based systems have also been installed in farm pontoons in Patagonia, Chile [43], snow ploughing vehicles in Gjovik, Norway [43], aircraft ground support vehicle [43] and piston driven car, America [43]. Such applications clearly indicate the utility of condensed aerosol based fire safety systems for the engine compartment of transport vehicles.

Snelle Vliet coach manufacturing company, Europe has also designed and installed, aerosol based bespoke units in the engine bay [39]. A low adhesion and low wheel grip of train on track were observed by Seoul metro subway in South Korea. This was because of leaves and dust particles present on track [39]. To prevent this, a special water cart is operated to clean the tracks with the jet of the water. This cart is operable all the time, so its engine needs to be protected from any kind of fire. Since the engine compartment of this cart was compact and a fire suppression system which take less space was required. Aerosol fire extinguishing systems were installed in the engine bay of this high-pressure locomotive. Bespoke aerosol units are also installed in the electric scooter in United Kingdom, Europe [39]. These scooters have small batteries at the back and are charged by simple household charger. There is a fire risk during charging of the scooter, so condensed aerosol fire extinguishing bespoke 20 g units are installed in the battery section considering the light weight and compactness.

2.3 Storage Rooms and Commercial Spaces

Fire protection of storage rooms such as warehouses, garages, cultural heritage storage, libraries, archives, museums, historical monuments is pivotal. The storage can also be of dangerous flammable items and chemicals which can easily catch fire if not taken care of. Commercial spaces such as hospitals, universities, malls, amusement parks have large public gatherings and protection of these places from fire is important as direct loss of human life is associated with it. The probable reasons of fire at these places may be due to electrical failure, wire fraying, loose connections, ignition of flammable chemicals, human mistake etc. Therefore, to prevent the buildings and storage rooms from fire hazard, an effective fire suppression system capable of extinguishing the fire in minimum time is required. Few case studies clearly indicated the replacement of gas or mist based systems with aerosol based systems. Various reports intelligibly indicate that aerosol based systems can be best placed to such areas as fire safety arrangements, Table 3.

Table 3 Application of Condensed Aerosol-Based Fire Extinguishing System in Storage Rooms and Commercial Buildings
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Two tests were conducted by BRE global Ltd. with Flame Guard BV on 4th august 2008 for ascertaining the effectiveness of aerosol suppression system for fire protection of prison cell of volume 36 m3 (3 m × 4 m × 3 m) [44]. The prison cell was furnished with a chair, a desk, 2 bunk beds a corner for toilet with temperature & gas sensors. A standard fire scenario was created, and aerosol system (aerosol generator unit with agent mass of 3.3 kg) actuated after 2 min of ignition/detection of fire. In both the tests, the time of aerosol discharge was 20–28 s. Aerosol generators were successfully able to put out the fire and no re-ignition was observed till 20 min.

For fire protection of vehicle storage facility for handicap people Hakuna Matata, AFX and KIWA performed fire test as per BRL K23001 certification guidelines on 1st October 2011 at AFX Oud Beijerland lab in Netherlands [45]. Aerosol systems supplied by AFX were installed at the bottom of storage and fire tests were performed against n-heptane pool fire with a pre-burn time of 240 s and inspection after 8 min. Fire successfully suppressed with no visual damage to the shelter.

John brooks et al. have discussed the application of aerosol grenades in high rise structural buildings, which are tough to reach and do not have total flooding system [46]. 40 MM aerosol generators (capacity: 250 g) combined with metal storm launchers are launched by law enforcement helicopters inside the building to extinguish fire. A case study by DSPA indicated the installation of aerosol systems in 42 m3 (7 m × 2 m × 3 m) electric meter room of a hospital in Mumbai for protection of MCBs, ELCBs etc. In another case study, aerosol based systems were installed in 18 m3 (2 m × 3 m × 3 m) computer server rooms in July 2011. After three months of its installation, on 11th Oct, EPABX cards damaged and smoke broke out due to lightning. Aerosol systems successfully extinguished the fire in early stage only [47].

In a renovation project of hospital in New York city, for fire protection of elevator machine rooms, wet pipe sprinkler systems were recommended by the NY state department of health but prohibited by the New York city building code [39]. To solve this problem, alternative fire suppression systems such as dry chemical systems, wet chemical systems, clean agent systems, carbon dioxide systems and aerosol systems were considered. First three fire extinguishing systems were found to be inappropriate because of slab penetration in traction of elevators. Carbon dioxide systems were also not considered as it raised the concern for the safety of life of the people in the elevator machine rooms and hoist way. Condensed aerosol systems were considered as a solution to all problems and installed in accordance with UL and NFPA.

Agrowin BV deals in consultation, marketing, and sales of agricultural & horticultural supplies such as fertilizers, pesticides, seeds etc. [43]. All these hazardous goods are stored in enclosed warehouse and may create explosive environment. Moreover, these goods and electrical equipment inside warehouse hold an intense fire threat. Foam based fire safety systems were earlier installed in store houses, but their operation and maintenances were itself a challenge. Therefore, foam-based systems were replaced with simple condensed aerosol-based fire extinguishing systems in compliance to the PGS-15 standards. Aerosol systems were also installed for the protection of chemistry laboratories having hazardous, flammable chemicals and some historical archives in Jagiellonian university, Poland [43].

In outermost part of Isle of Wight in Britain, needles lighthouse was constructed in 1859 with height 33.25 m above sea level [43]. Fire in any electrical panel or the power generators can lead to a catastrophic event. Earlier, HFC227ea cylinders were deployed in the generator rooms but since the lighthouse is present in a remote offshore location, maintenances of these pressurized cylinders were itself a task. Therefore, the trinity house company replaced the HFC227ea suppression systems with aerosol extinguishing agents as they are light, easy to maintain and have simple installation.

Princess Elisabeth Antarctica is the world’s first zero emission scientific research center laid by International Polar Foundation [43]. The research center has a wooden structure and is equipped with expensive sensitive scientific instruments. To prevent them from fire, water mist systems were installed earlier in the roof level UPS rooms. The remote location of this research center possessed a great challenge in the transportation and logistics of fire suppression systems. So, water mist systems were replaced with bespoke aerosol firefighting systems.

Condensed aerosol systems were also installed in electrical panels and high voltage rooms of Paphos general hospital and Chelsea & Westminster hospital of Europe respectively [43].

CAFES also found application in the protection of paint spray booth of media capital group in Europe [43]. These paint spray booths use several chemical substances such as acetone, thinner, paint, alcohol and varnish which become major ignition sources for fire outbreak.

Pharmaceutical manufacturing and distribution corporations such as Pfizer Inc. (Egypt) and Dr. Reddy’s laboratories (Hyderabad), Brenntag (Europe) [43] store flammable chemicals, medicines, and vaccines in storage facilities. Since the storage rooms are filled with diverse materials, a fire extinguishing system capable of extinguishing all classes of fire (A, B, C and F) was required. Therefore, aerosol fixed units have also been installed in the malls, smart parks, retail stores etc. for the protection of electrical panels, diesel generator rooms and electrical substations [43]. Overall, condensed aerosol-based fire extinguishing systems have found application as such or as replacement of gas and mist-based systems in warehouse, electrical panels, diesel generator rooms, storage rooms, buildings, hospitals etc.

2.4 Power Generation

Wind energy, hydro electrical energy, biomass energy, solar energy are the different renewable energy sources, which are getting huge attention in renewable energy sector. Fire in any of these assets can cause large damage to the companies as well as endanger lives. Fire can be caused due to many reasons such as defects in the designing, overheating, leakage of current, poor maintenance etc. Fire can be minimized by employing reliable and effective fire suppression systems. Aerosol based systems (CAFES) have been installed at these renewable energy infrastructures in many countries, Table 4.

Table 4 Application of Condensed Aerosol-Based Fire Extinguishing System in Power Generation
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Fire is the biggest challenge of wind energy industries. There are many causes of fire in wind turbines such as lightning strikes, accidental failure of its parts, electrical malfunction etc. [48]. Almost 200 gallons of flammable hydraulic oil and the nacelle materials (flammable glass fibers and resins) are the immediate fire hazards. Due to remote installation locations, it was very tough to install bulky fire protection systems such as FM 200, Novec 1230, CO2 and water-based systems. CAFES have also been installed in the nacelle and electrical cabinet at base of the 120 feet wind turbine of SAESA in Aysen, chile [43]. Condensed aerosol-based fire extinguishing systems are the best option as they are easy to install, needs minimal maintenance, have a modular design, and can withstand environmental factors. In another application, CAFES was installed in nacelle of a 100 m high wind turbine with 70 m rotor diameter in Asia [39].

CAFES have also been installed in the bio-gas power plants such as in Bioario Pellas, bio-gas power plant, Greece [39] and Agro Energiek, renewable energy producing company, Europe [39]. In a bio-gas plant, a large amount of highly flammable biogas is generated from manure, vegetables, and all kind of kitchen wastes. Any malfunction in the electrical equipment of the power plant can directly originate the fire.

2.5 Heavy Industries

Heavy industries such as mining, food packaging & processing, pulp & paper processing, wood processing, water refining, petrochemical, pharmaceutical, automobile manufacturing etc. play a crucial role in development of a country. These industries may have many fire hazard areas/parts/systems such as transformer rooms, generator rooms, engine rooms, compressor rooms, UPS systems, control rooms, electronic cabinets etc. The risk of fire accidents is always high as the electrical and electronic equipment are constantly energized and heated, and the short circuit may happen any time. Condensed aerosol-based fire extinguishing systems are being considered worldwide for such fire safety applications. The successful installation of aerosol based systems has been indicated in many case studies as shown in Table 5.

Table 5 Application of Condensed Aerosol-Based Fire Extinguishing System in Heavy Industries
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Akritas a wood processing industry in Europe installed CAFES in the transformer rooms and substations [39]. Perenco oil and gas industry installed aerosol systems in the electrical rooms situated at gas condensate fields [39]. In mining industries, a constant threat of fire and explosion is there to the miners because of the use of various electrical equipment. Considering that, Glencore plc, trading and mining industry in Australia, installed fire detection and aerosol suppression system in electrical substation and power transformers at 1.8 km underground of mount Isa mines in Queensland [39].

Various industries have given more emphasis to the fire safety of electrical panels, electrical cabinets, power transformers, electrical substations, UPS, and control rooms. Industries such as Kumi A-TECH solutions (molding and double molding device manufacturing), Sappi group (pulp and paper manufacturing), Tetra pack (food packaging and processing), Theoni water A.H.B. group S.A. (bottled water manufacturing), FAMAR (pharmaceutical products), European metal recycling (scrap metal recycling), Egyptian LNG (LNG liquification), Renault Samsung motors (car manufacturing) [39], etc. have considered aerosol based fire safety systems to counter electrical fire accidents.

A fire accident took place in a 20,000-gallon mixing container of a roofing material manufacturing industry [43]. The fire further spread into other sealed containers via duct area. To prevent this kind of fire spreading, industry considered two alternative fire suppression systems, viz., carbon dioxide based and aerosol based. Both the systems were considered based on various parameters such as floor space, duct maintenances, cost of equipment and installation. With CO2 based systems, there was a requirement of large cylinders, piping network along duct area, expensive piping & nozzles and costly installation. Whereas aerosol based fire suppression systems indicated no hefty cylinders, no piping and inexpensive installations. Therefore, to prevent the deep-seated fires in containers and their spread, aerosol fire suppression systems were installed.

A standalone fire protection generator with detection and release system was installed in the CNC machines of a specialized machine parts manufacturing industry [43]. As in-service scenario, a fire broke in one of the CNC machines in less than a year of installation of aerosol system. The detector sensed the fire as soon as it was originated, aerosol discharged, and fire was extinguished successfully. No damage caused to the equipment and human lives.

2.6 Commercial Marine

Fire safety of marine vessels be it a small boat, yatches, tugboat or a big shipping vessel, is always a difficult task as the fire accidentally originate at middle of the sea. These vessels sometimes even carry flammable materials, which can catch fire. Therefore, considering the environmental conditions of seas/oceans and escape possibilities, it is of paramount importance to deploy an effective fire extinguishing system. Aerosol based systems have been considered due to their effectiveness, low weight and maintenance free installations, Table 6.

Table 6 Application of Condensed Aerosol-Based Fire Extinguishing System in Commercial Marine
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European super yacht ship building company, Heesen Yachts, has designed a luxury yacht YN 17,145 [39]. There are engine compartments, battery rooms and electrical cabinets, which possess a high fire risk due to electrical faults. A bespoke fixed aerosol fire suppression system has been installed in 193 m3 engine room of the vessel. ARK yatches is the leading company in designing and engineering of steel & aluminum sailing and motors yatches in Europe [39]. They have designed a CHRONOS luxury yacht which is 55 m in height and can accommodate 26 people and 8 crew members. Fire in this yacht can originate from electrical equipment, engine compartment and may be due to human errors. In overseas vessels, weight and space is always an important factor. Therefore, fixed units of condensed aerosol-based fire extinguishing systems were installed in accordance with International Marine Standards (MSC.1/Circ.1270).

Miss GIECO is the offshore world champion powerboat racing team. In 2012 during a race, this powerful high-speed boat caught an internal fire and was immersed in flames [43]. The flame originated from the engine compartment and even took the traditional HFC fire protection system into its flames. Now, 4th generation miss GEICO is under advancement and required a fire extinguishing system which is reliable. Earlier installed HFC gaseous systems are bulky, require distribution pipelines and have high ozone depletion potential. These cylinders are under high pressure all the time and any vibration can cause leaks and be lethal for the crew. Therefore, traditional HFC systems were replaced with small, self-contained and piping less aerosol based fire detection and suppression system.

2.7 Defence

Condensed aerosol-based fire extinguishing system have been broadly used in all the defence forces such as navy, air force and military for the protection of machine rooms, engine compartments, gas turbine enclosures, electronic equipment bays & galley of aircrafts, diesel generator rooms, pump rooms etc. Various test and evaluation reports/case studies are available in open literature indicating the effectiveness of aerosol based systems, Table 7.

Table 7 Application of Condensed Aerosol-Based Fire Extinguishing System in Defense Platforms
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2.7.1 Naval Platform

United States Coast Guard conducted several fire tests in 2006 with aerosol based systems for shipboard machinery spaces [49]. The aerosol extinguishing systems of three companies namely Ansul, FirePro and Flame Guard were used for extinguishment of class A and class B fires. All the tests were conducted as per International Maritime Organization’s (IMO) test protocol maritime safety committee (MSC/Circ. 1007). Tests were performed on aboard the test vessel in a simulated machinery space. The test compartment had dimensions (10 m × 10 m × 5 m) with total volume of 500 m3. According to MSC/Circ. 1007, the discharge time of aerosol must be less than 120 s and the fire must be extinguished within 30 s of discharge of aerosol. Various equipment was installed in the compartment for assessing parameters such as thermal conditions, particulate density, gas concentration, video imaging and fuel system pressure. All the three systems were found to be effective in extinguishing class B fire, but difficulties were observed in extinguishment of class A fires.

Martin Connell and Dr James LD Glockling reported the large-scale testing of pyrotechnically generated aerosol fire extinguishing system in T45 destroyer Royal Navy warship for protection of machinery spaces and gas turbine enclosures [50]. The fire hazard was mainly diesel, hydraulic oils, and electrical cables. In 2004, warship integration team opined to replace carbon dioxide fire suppression system because of its disadvantages such as high maintenance cost, extra weight due to cylinders and potential risk to personnel on leakage. Aerosol based fire extinguishing systems were considered as replacement due to their light weight, easy installation, and maintenance. Fire tests were performed in 500 m3 enclosure, following MSC/Circ. 1007 IMO protocol guidelines. Slow and rapid discharge systems were evaluated. For rapid discharge system, two 6 kg and six 11 kg units were used with a design concentration of 128 g/m3, but it could not put out most of the fires. With slow discharge systems (56 units of 1.1 kg agent each) most of the fires suppressed. Slow aerosol discharge systems were considered by T45 designers for protection of switchboard and diesel generators.

T Goode in his review discussed the advantage of using aerosol fire extinguishers over other halon alternatives such as water mist, carbon dioxide, inergen, aragonite, FM 200 and NOVEC 1230 [51]. Aerosol fire suppression system approved for installation in small vessels with 64 m2 floor area and 4 m height by Maritime Coastguard Agency (MCA). The system has also been installed in US landing craft utility (LCU) to replace halon and in US LPD flammable stores. R. S. Sheinson et al. discussed intermediate testing of pyrotechnically generated aerosol fire extinguishing particles in 56 m3 compartment (4 m × 3.4 m × 4.3 m) in Chesapeake Bay detachment (CBD) [52]. Three different types of fire extinguishing generators (hot, passive water bath and water spray generators) were used against n-heptane pool fire (0.8 m × 0.3 m). Various sensors/analyzers were also installed inside the compartment. Fire tests with pre-burn time of 45 s indicated that 3 and 4 kg hot aerosol generators extinguished the pool fire in 115 and 45 s respectively. 3 kg water bath generator could not extinguish the fire, but 5 kg system extinguished it in 115 s. 3 kg water spray generator extinguished fire in 65 s.

Navy of Finland installed aerosol suppression systems in the fuel barge of the cargo ship KAMPELA, which is used for the transportation of flammable liquids [53].

A series of fire tests was conducted using aerosol systems in 35.3 m3 (6.1 m × 2.4 m × 2.4 m) shipping container at brush traction, Loughborough [53]. To simulate a complete machinery space, a model was constructed in the container with engine and bilge system. In accordance with maritime and coastguard agency norms, series of tests such as open pool fire, hidden spray fire, hidden pool fire, combined open pool/hidden spray fire, combined open pool/hidden pool fire, combined hidden pool/hidden spray fire, combined open pool/hidden pool fire were conducted. Lubricating oils, heptane and diesel were used as fuels. Thermocouples were arranged to measure the temperature at various locations. 2- and 5-min pre-burn time was given for pool fire and diesel spray fire, respectively. Generators were activated, and after 10–15 min of discharge doors were opened. Fire extinguished successfully in all the seven test fires.

Kokchen Yang/Richard Lee reported about a fire accident which occurred in the engine compartment of PK30 patrol boat of Singapore police coastguard on 12th may 2001 [53]. The reason for fire was combustion & disintegration of the rubber seal band at the outlet due to overheating of port side engine. Three aerosol based systems earlier installed in the engine compartment successfully activated and extinguished the fire without any permanent staining or discoloration of the engine surface.

J. Berezovsky, AES international Pvt. Ltd. conducted several fire tests to investigate the fire extinguishing efficiency of systems for a 33.5 m3 engine room of a commercial shipping vessel [53]. The test chamber had open fire trays in machinery space and bilge mock-up with ventilation dampers. Four tests were conducted: two with pan fire {blank test with no agent, with 2 MAG4 generator (59.7 g/m3 design concentration)}, and two with spray fire {with 3 MAG4 generator (89.6 g/m3 design concentration)}. Pre-burn time of 2 min and 15 s was given to pan fire and spray fire respectively. Aerosol system activated and the door opened after 3 min of aerosol discharge. Aerosol generators successfully extinguished the pan and spray fire in 17 and 10 s, respectively.

For fire protection of 5.7 m3 engine enclosure of small gas turbine power plant, experiments were conducted with aerosol and water mist fire suppression technology [54]. The turbine enclosure had two leakage holes of area 0.175 and 0.122 m2. Heptane pan and spray fires were used as fire sources having intensity of 18–100 kW fire. Two aerosol generator units with 85:15 & 65:35 gas to powder ratio and 109 & 60 g/m3 design concentration, respectively. Two spray nozzles with total flow rate of 2.6 & 0.45 LPM/m3 volumetric flux were used for water mist fire suppression tests. Water mist system extinguished fire but with higher design water flux than expected. Aerosol agent successfully extinguished the fire in 30 s and no re-ignition was observed till 15 min. Overall, test results clearly indicated the superiority of aerosol over water mist meeting all the requirements and objectives at one third weight impact.

Canadian Coast Guard (CAG) is responsible for all search & rescue, navigation, communication, and transportation issues in the Canadian waters [39]. 19 m long CAG lifeboats can have 10 people on board. The fire risk is due to diesel room, engine compartment, leakage of fuel and human errors. To provide fire safety CAG asked Navware, Canada to provide bespoke engine room fire detection and suppression system for 20 search and rescue lifeboats. All the sea vessels and boats required space saving and light weight systems with least maintenances. Therefore, condensed aerosol-based fire extinguishing systems were installed. Kenya Ports Authority installed aerosol detection and suppression system in 12 electronic equipment and substations of Kenya port [39].

2.7.2 Air Force Platform

A joint program between the US Air force and a private sector developed a new kind of fire suppressant known as Encapsulated Micron Aerogel Agent (EMAA) [55]. Charles J. Kibert and Douglas Dierdorf conducted several experiments to assess the performance of EMAA against n-heptane and brown paper fire. 10–20 g EMAA positioned at mid chamber and chamber floor suppressed n-heptane pool fire at extinguishing concentration of 50 g/m3. EMAA proved six times more effective than Halon 1301 (extinguishing concentration: 300 g/m3). EMAA found applications in UPS rooms, fuel storage tanks and engine compartments. In another report, national oceanic and atmospheric administration (NOAA) used aerosol fire suppression systems for the protection of electronic pods of the WD-3D Orion aircraft wing stations for new England air quality study (NEAQS) project [53]. CFCs and HFCs based systems have pressurized cylinders and leakage possibilities, therefore, aerosol based systems were preferred over gas based systems.

Naval Research Laboratory conducted fire tests using aerosol systems in B-737 EE bay (12 m3) and aircraft galley (1 m3) at Memphis group facilities, Greenwood, Mississippi [53]. 128 polyimide 20 gauze electrical wires removed from the interior of the testing aircraft were suspended over class B fuel (kerosene) as the fire source and 12 systems with design concentration of 200 g/m3 used as fire extinguishers. Six additional 25 mm fuel cups were placed in various locations in the electronic equipment (EE) bay and radar bay to see the total flooding of the aerosol system. For the galley tests, galley was removed from the interior of another aircraft and wire bundles & cups were placed on the bottom floor. Fuel was ignited with a pre-burn time of 60 s, and aerosol was discharged. Fire extinguished successfully within 2 s of discharge of the agent and no re-ignition was observed.

2.7.3 Military Platform

The US Department of Defence produced more than 9700 all-terrain mine resistant ambush protected vehicles (M-ATVs). MOD’s of kingdom of Saudi Arabia and United Arab Emirate also have 2000 and 1000 M-ATVs respectively [43]. In the battlefield, fire can occur in the engine bay of these armored vehicles due to several reasons such as fuel leakage, electric short circuits, explosions etc. To protect the engine bay of M-ATVs, aerosol fire extinguishing systems have been installed considering space, weight, and material requirements.

Carnegie Mellon University is involved in building and testing of robotic tactical unmanned ground vehicle (UGV) for remote combat tasks [53]. For protection of electronic bays and communications systems, aerosol generator was installed containing 20 g of aerosol forming compound, and for larger areas generators with 100 g aerosol forming compound were installed. Overall, the literature clearly indicates that condensed aerosol based fire extinguishing systems have found versatile applications in providing fire safety to defence platforms. Various other defence areas can still be approached for fire safety using aerosol based systems.

3 Conclusion and Future Prospects

A lot of research is going on worldwide for development of aerosol forming compounds and cooling pellet composites for electrical, non-electrical, cold, and hot versions of CAFES. Research is also in progress in developing hybrid systems, which accompany aerosol technology with other efficient fire suppression technologies/chemicals. Nowadays, green chemistry is gaining a lot of momentum. This also attracts attention to the modification of aerosol forming and cooling pellet composites, utilizing environmentally friendly ingredients for its preparation. In some cases, traces of toxic gases such as carbon monoxide, nitrogen oxides, hydrogen cyanide, methane are also generated along with aerosols, that is why they are not employed for use in occupied areas. Till date aerosol-based fire extinguishing systems were only approved/listed for non-occupied areas, but now Stat-X has come up with an aerosol system listed as powdered aerosol D approved by US EPA SNAP for occupied areas. Systems with other brands also need more research on advancement of aerosol systems for fully occupied areas.

Condensed aerosol-based fire extinguishing systems have demonstrated their proficiency in extinguishing all classes of fire. CAFES indicated many features such as less space requirement, no hefty piping, most efficient on the basis of weight to volume requirements, low maintenance, zero ODP & ALT, negligible GWP, modular structure, low installation cost, etc. over the other fire safety technologies. Overall, limited drawbacks with aerosol-based systems attract its widespread applicability, practically in all enclosed areas as total flooding system. As a result, it is being considered worldwide for versatile applications including power generation systems, energy storage systems, storage rooms, commercial buildings, transportation, heavy industries, defence platforms etc. It is extensively used for fire protection of cars, buses, locomotives, warehouses, garages, heritage buildings, libraries, control rooms, UPS rooms, electrical panels, machinery spaces, generator rooms, engine rooms and gas turbine enclosures. For targeted fire suppression, grenade or handheld devices of aerosol based systems are used. Moreover, considerable progress has been made in recent years to improve the effectiveness of aerosol-based systems in suppression of fire for several applications. Still many areas (lithium ion battery fire, metal fire etc.) are left where the applicability of aerosol based systems to be checked and application based protocols/standards to be evolved.