Water has been used to fight f…

11 November 2018

Water has been used to fight fires throughout history in all types of environments, applications and methods. This is mainly because water in considered inert and has the scientific properties to make it a great fire suppressor (Liu & Kin, 1999). Water has a high heat capacity, requires a large amount of energy to vaporize, can absorb large amounts of heat, and expands when it evaporates diluting the surrounding fuel and oxygen sources (Liu & Kin, 1999). Water is also readily accessible in most parts of the world, environmentally friendly, and cheaper to uses than any other methods of fire suppression. This is why it continues to be the most sought after fire extinguishing agent.
The National Fire Protection Association (NFPA) standard on Water Mist Fire Protection Systems or NFPA750 defines water mist as “a water spray for which the Dv0.99 [99%], for the flow-weighted cumulative volumetric distribution of water droplets is less than 1000 um within the nozzle operating pressure” (NFPA, 2015, Definitions, para. 3.3.22). The European Committee for Standardization defines water mist in its CEN/TS14972 as “a water spray for which the 90% of the total volume of liquid (Dv0.90) is distributed in droplets with a diameter smaller than 1000 microns at the minimum design operating pressure of the water mist nozzle” (VID, n.d.). These definitions are a little confusing but are attributed to an earlier time when droplet size was the only consideration for performance (VID, n.d.).
The operation of misting systems is relatively simple. Pressure pushes water through a nozzle or series of nozzles to create a cool, fog-like mist. This mist is suspended in the air due to its small droplet size and is transported throughout the area by turbulent air. The mist performs much a like a gas in the sense it can move around objects and get into crevices and ventilation systems. Surface wetting is still the primary method of fire suppression and helps keep the fire from spreading but it is not a complete saturation like traditional sprinkler systems (Stanwick, 2003). This wetting is assisted by cooling of the surrounding areas, surrounding air, fire, and fuel source (Stanwick, 2003).
Another benefit of water misting is the scrubbing effect. In simple terms, smoke is made of liquid and solid particles created through the combustion of the fuel source (Stanwick, 2003). These small particles stick to the water droplets cleaning the air from harmful particles (Stanwick, 2003). This can be an important factor in the ability of this technology to save lives. According to the NFPA, prior to 1999 smoke inhalation deaths outnumbered burn deaths three to one (Hall, 2011). After 1999, there is a two to one ratio for smoke inhalation versus burn deaths (Hall, 2011).
Today there are a number of factors that affect water mist performance. As previously mentioned, the surface area of the spray being used has a direct effect on how it reacts with the fire (Hambling, 2001). A normal sprinkler droplet size of one millimeter has a water surface area of two square meters (Hambling, 2001). A mist spray of one-tenth a millimeter across can have a surface area of more than two hundred square meters (Hambling, 2001). To put this into perspective, in one test a fire temperature was decreased approximately five hundred degrees centigrade and extinguished in two seconds using a mist (Hambling, 2001). That is extremely efficient fire fighting and explains why previously droplet size was considered so important. Smaller droplets also have a much longer hang time in the air (Liu & Kin, 1999). This can help them be carried to small crevices and other areas inaccessible by larger droplets (Liu & Kin, 1999).
Spray flux density is another factor that affects water mist. Spray flux density is the amount of water spray in a unit volume or unit area (Liu & Kin, 1999). The spray flux density must be increased enough to remove heat from the fire, cooling it below the ignition point (Liu & Kin, 1999). The more it increases the less effect it will have on oxygen in the area. This is why certain heads with spray patters are tested first prior to use. The correct equilibrium must be met for the situation and fuel to optimize the effects and the spray mist (Liu & Kin, 1999). The mist must reach the fire to be effective and a fire that creates more heat than the cooling power of the mist will not be extinguished (Liu & Kin, 1999). This can further be affected by spray momentum, spray angle, shielding of the source, size of the fire, airflow, size of the area and shape of the area (Liu & Kin, 1999).
The last factor affecting water mist performance is the spray momentum (Liu & Kin, 1999). This is the spray velocity and its direction in reference to the fire (Liu & Kin, 1999). This has a direct impact on the droplets ability to penetrate the fire and contact the fuel source (Liu & Kin, 1999). The spray momentum produces air turbulence which helps circulate the water droplets (Liu & Kin, 1999). This circulation helps reduce the amount of oxygen and fuel vapor which in turn helps extinguish the fire (Liu & Kin, 1999). The factors that affect spray momentum are droplet size, droplet velocity, pressure, angle, nozzle spacing, airflow, area size, and area shape (Liu & Kin, 1999).
The history of misting systems can be traced back to around 1880 and the F.E. Myers company (Lakkonen, 2008). Their creation of the back-bag system included a lance utilizing small water droplets to fight forest fires (Lakkonen, 2008). The biggest drawback of the time was lack of pressure and it wouldn’t be until the 1900’s that further advancement would be made in this area (Lakkonen, 2008). As better sealing materials were improved and created, the ability to increase pressure advanced and by the 1930’s there were multiple companies offering systems that utilized misting technology in their products (Lakkonen, 2008). They were promoted on the benefits of cooling effect, oxygen displacement and low water damages with use (Lakkonen, 2008). One such company marketed a multiple orifice nozzle called a water dust nozzle (Lakkonen, 2008).
In the 1940’s another company, Factory Mutual, carried out a series of tests with small droplet nozzles and their effectiveness on gasoline fires (Lakkonen, 2008). The results indicated that the performance was comparable to conventional sprinkler systems except flow rates were much lower (Lakkonen, 2008). During this period, fire fighting techniques with water mist were established and the USA and Europe adopted water mist techniques as a manual fire fighting strategy (Lakkonen, 2008). The effectiveness of misting during the period was well recognized but it was still not utilized for fixed applications (Lakkonen, 2008). This was mainly due to the lack of water pressure in the systems that supplied water if any where yet available (Lakkonen, 2008).
For the next twenty years there was a period of independent research but no systematic trials (Lakkonen, 2008). The creation and investigation into gases and powder as a fire suppression agent became the mainstream focus (Lakkonen, 2008). These systems were integrated into or along with the conventional sprinkler systems (Lakkonen, 2008). Misting was only considered effective and used in a select portion of the industry, manual fire fighting (Lakkonen, 2008).
Around 1970 there were breakthroughs with supporting technologies such as hydraulics, which helped increase the working pressure of the manual firefighting systems (Lakkonen, 2008). This helped create several research groups that were researching misting technologies in different parts of the world (Lakkonen, 2008). By 1980 there was some misting products installed in a number of industrial and public buildings such as the Leipzig Bowling center in Germany (Lakkonen, 2008). The biggest breakthroughs were from Sweden where researches developed new tactic for fighting fires (Lakkonen, 2008). Krister Giselsson and his partner Mats Rosander termed their new tactic “offensive fire fighting” (Lakkonen, 2008). This new tactic applied misting sprays to indoor fires in short bursts (Lakkonen, 2008). This helped to cool the combustion gases without large amounts of thermal imbalance and without large amounts of scalding hot steam (Lakkonen, 2008). The creators then took the information they collected from the offensive fire fighting and began creating one of the first fixed water misting systems (Lakkonen, 2008).
They would co-operate with the company Electrolux Euroclean (Lakkonen, 2008). Electrolux Euroclean was in the business of industrial cleaning equipment and was inspired to join fire misting when their equipment was accidently used to put out an oil fire (Lakkonen, 2008). Electrolux Euroclean would carry out a number of tests at the Swedish research institute proving the performance of their product and to give baseline scientific references where previously there were none (Lakkonen, 2008). This unusual team organized several demonstrations and fire tests between 1981 and 1983 providing an increase in the general knowledge of misting in Sweden and surrounding areas (Lakkonen, 2008).
In the 1980’s the Montreal protocol was signed being finalized in 1987 (USDOS, n.d.). This global initiative protected the atmosphere by stopping the production and use of ozone depleting substances most notably chlorofluorocarbons (CFC’s) and halons (USDOS, n.d.). Halon was widely used at this time as a fire suppression agent and this started the search for viable alternatives (USDOS, n.d.). The Significant New Alternative program (SNAP) was started by the U.S. Environmental Protection Agency helped develop a class of clean agents and renewed interest and funding for research in water misting systems (USDOS, n.d.).
Another incident in 1990 would also help water mist technology. The ferry boat Scandinavian Star had a fire break out on the morning of April 7th 1990 (Scandinavian Star, n.d.). The cause of the fire is suspected to be arson but the loss of 159 people is what brought negative publicity on the marine industry (Scandinavian Star, n.d.). Experts franticly searched for fire suppression methods that did not have the weight, large piping requirements, or high water requirements of standard systems to be installed into ships (Lakkonen, 2008). This event also leads to the successful fire demonstrations in Balsta Sweden on 20 June, 1990 (Lakkonen, 2008). These demonstrations were attended by shipping companies, insurance companies, fire and rescue services, and other marine industry companies (Lakkonen, 2008). It is considered a major turning point for water misting systems and the first large marine installations are realized in 1992 onboard Motor Ship Danica, Motor Ship Festival, and Motor Ship Karneval (Lakkonen, 2008).
The modern age of water mist technology had begun and was further supported by the International Maritime Industry (IMO) (Lakkonen, 2008). The IMO had multiple resolutions in the mid 1990’s that would increase the support and use for this technology aboard ships (Lakkonen, 2008). These resolutions would require the latest safety technology and require features incorporated similar to that of a hotel or building (Wilmot, 2016). The National Fire Protection Agency (NFPA) would create a technical committee on Water Mist development and release the first standard, NFPA750 Water Mist Fire Protection, in 1993 (Lakkonen, 2008). In 1998 the International Water Mist Association (IWMA) was formed with five corporate members (Lakkonen, 2008).
Water misting systems have become even more popular through recent years and have been further investigated by all branches of the military (Lakkonen, 2008). The IWMA has swelled to over fifty corporate members and now holds an annual conference that supports the misting industry (Lakkonen, 2008). This old technology has had resurgence due to continued advancements and the events previously discussed. Misting is now common in a number of industries and is continuing to increase in popularity. Today water misting technology is marketed with advantages such as: immediate activation, high efficiency, minimized damage, environmentally friendly, and non toxic (ORR, n.d.).
One of the most recent advances in misting technology is the PyroLance. The PyroLance is a portable, high pressure, fire fighting system utilizing misting technology (Schroeder, 2011). It consists of a high pressure lance, a high powered pumping unit and the hoses to connecting the two (Schroeder, 2011). It comes in three different models that can be operated by gas, diesel or power take-off and has a variety of options including: wireless controllers, wireless repeaters, upgraded hoses, extending hoses, mounting systems, water tanks, foam tanks, and abrasive material (Schroeder, 2011).
Traditionally firefighters enter a structure to actually engage the fire (Roe, n.d.). This can risk the lives of those trapped inside and the firefighters by introducing more oxygen to the fire (Roe, n.d.). The situation can then escalate becoming more serious through flashovers, back drafts or an explosive type environment (Roe, n.d.). This product is unique because it changes traditional thinking on how to fight fires and can be used in situations that are difficult for fire fighter such as smoldering material between walls or structure panels.
The PyroLance is held by the firefighter against the exterior wall or structure of the target and initiates the system (Schroeder, 2011). This activates the high pressure water stream mixed with aggregate which bores a 3mm hole through the target (Schroeder, 2011). The firefighter can then switch the aggregate off and initiate the high pressure water system (Schroeder, 2011). This provides a misting spray to the interior of the targeted location with water, foam, or combination of the two, cooling the targeted area and associated fire (Schroeder, 2011). The company’s website claims a fire reduction of 900 degrees in less than one minute and that the boring is effective against any type material including steel, concrete, brick, stucco, and wood (Schroeder, 2011).
The United Stated Air Force (USAF) conducted extensive testing on PyroLance to characterize the piercing and fire extinguishing capabilities of the system (Schroeder, 2011). Their testing was conducted in accordance with the NFPA 412 Standard for Evaluating Aircraft rescue and Fire-fighting Foam Equipment, Section 6.3.2 (3) (Schroeder, 2011). They evaluated flow rate, foam quality (not discussed here), throw distance, maximum piercing distance between two composite plates, multiple panel piercing ability, and ability to extinguish hidden fires between two panels (Schroeder, 2011).
The finding of this testing concluded that this system is very easy to use to pierce an aircraft and apply water or foam to a fire (Schroeder, 2011). Throw tests were determined by placing a series of small fires at various distances and the then measuring to the furthest extinguished fire pan (Schroeder, 2011). The results indicated that the system was effective up to thirty-five and a half feet (Schroeder, 2011). Maximum piercing distance was completed by increasing the separation distance between two panels until they both could not be penetrated (Schroeder, 2011). This test concluded that the system could be used to pierce two aircraft panels separated up to eight feet (Schroeder, 2011). Multiple panel piercing ability was tested by organizing multiple panels at twelve inch intervals and seeing how many/how far the system could penetrate (Schroeder, 2011). This multiple panel piercing test concluded that the system is capable of penetrating five .153 in thick aircraft panels separated by twelve inches in between (Schroeder, 2011).
Ability to extinguish hidden fires between two panels was completed by following the Federal Aviation Association Aircraft Cargo Compartment Minimum Performance Standards for containerized fires (Schroeder, 2011). This test utilized an LD-3 container, eight thermo couples to monitor temperature and empty cardboard boxes stacked inside (Schroeder, 2011). There were also two twelve inch by three inch slots cut into the sides for ventilation (Schroeder, 2011). Two tests were conducted and the internal temperature was reduced to below 110-120 degrees Fahrenheit but the fire did continue to smolder and was not completely extinguished (Schroeder, 2011). This study concluded that the USAF should continue with additional studies to investigate effectiveness of the system to extinguish compartment fires using water, water foam and heat absorbing gels (Schroeder, 2011). The results of this test were primarily designed to study the piercing ability and not designed for its firefighting success (Schroeder, 2011).
There were also a number of recommendations made to help improve the system (Schroeder, 2011). Thos recommendations are: minimum flow rate of the system be at least 10 gallons per minute, the overall weight of the lance needed to be lowered due to the high firefighter fatigue sustained while using the system, the shoulder support should be modified to avoid conflict with the self-contained breathing apparatus (SCBA), install a power switch on the lance, install and alternator for automatic battery recharging, and lastly resolve the issue with aggregate mixing with water when not actuated (Schroeder, 2011).
This study indicates that although the PyroLance system may not be ideal for all situations, it is an excellent tool that can advance the available options to the firefighter. It also supports continued research be conducted for this system to be further perfected. A number of high profile organizations have already added this tool to their firefighting capabilities including the USAF, United States Navy, Dallas-Fort Worth Airport, and many municipalities across the United States. It is extremely popular in other countries including Canada, United Kingdom, Sweden, Germany, Dubai, and is growing its fan base through exhibits and demonstrations at popular events.
The advancement of misting technology has been continual since its inception and has increased with a better scientific understanding of how the technology works. Water misting is a viable alternative to traditional sprinkler systems and in areas where water damage from traditional systems is of concern. Currently, misting systems are designed for both solid fuel and liquid fuel fires and are continuing to challenge other portions of the fire protection market. The PyroLance is a great example of the versatility of this technology opening new markets and challenging traditional views. It is a fire fighters tool that should not be overlooked in the quest for saving lives and preventing injury. Does your municipality have this tool in their arsenal?

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