Topic: Fire Protection Systems

Inside a warehouse

Do you manage large warehouse facilities, or design, inspect or insure them? Help us define the elevated walkways in storage warehouses to quantify their impact on sprinkler protection by participating in this questionnaire

Solid and open metal grate walkways are often installed in aisles as part of rack storage in large warehouse facilities. Further, open metal grates are also used as mezzanine levels above storage. Although functional to carry out warehouse operations, there is little information on how these walkway and mezzanine installations impact current storage protection requirements. When is this type of installation considered a problem from a sprinkler protection standpoint? At what point do walkways interfere with prewetting of adjacent arrays? To answer these questions, the Fire Protection Research Foundation (FPRF) initiated a multi-phase research program, through the support of FPRF’s Property Insurance Research Group, which aimed to develop guidance on the protection of storage when solid or open metal grate walkways are present in storage warehouses.  FPRF, in collaboration with Fire & Risk Alliance, is currently on Phase II of the project which is focused on filling the knowledge gaps identified in Phase I and implementing the research and testing plan to provide guidance back to the NFPA 13 technical committee on walkway/sprinkler interface criteria that is well founded in sprinkler performance. For more information, a summary of this project is available here. A fundamental element of success for this study is to collect information on current warehouse configurations to gain insight into the status quo characteristics of elevated walkways/mezzanines and how storage protection may be changing. Thus, we invite facility owners, AHJ’s, insurers, engineers, and other relevant parties to participate in this international questionnaire conducted as part of this study by the Fire Protection Research Foundation. The questions seek to identify and categorize the types and non-proprietary characteristics of elevated walkways in storage warehouses, specifically focused on storage configurations, stored commodities, details of mezzanine/walkways, sprinkler system details, loss history (if any), and photographs or drawings. This information will be used to ensure our analysis of sprinkler interaction with or disruption by elevated walkways is representative of real-world warehouse configurations. Your participation in this research questionnaire is voluntary. You may skip any question that you are not able to answer. Any information provided through this survey is completely anonymous. If you design, work in, inspect, or insure warehouses with elevated walkway installations, we ask that you participate in this survey. It is estimated that the survey will take approximately 10 minutes or less to complete. The deadline to complete the questionnaire is August 31, 2022. Thank you in advance for your participation!
Man inspecting and looking at a tablet

Automated and Remote Inspection and Testing of Water-Based Fire Protection Systems

Remote inspections and automated testing were trends that were gaining momentum in codes and standards and field application for several years. Then in the first half of 2020 when the COVID-19 pandemic was in its early stages and strict lockdowns were being enforced, it pushed this trend to progress even faster as many more realized its potential. During this time, the development of a proposed new standard NFPA 915, Standard on Remote Inspections, continued. While the proposed NFPA 915 will be broadly applicable to any inspection or testing allowed by the AHJ, there are already provisions in NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, that allow for inspections and tests to be conducted in an automated manner. Automated inspection and testing can be a very useful option but what steps must be taken to ensure it is equivalent to a person being at the location? If a fire pump demonstrates an abnormal condition during a test what must the response be and how is the condition corrected? Let’s take a look at the requirements in NFPA 25 to allow the use of technology for automated inspection and testing and the criteria to ensure it meets the same objectives as when they are conducted in person. The first thing to address is when and where automated inspection and testing can be utilized. NFPA 25 does not limit the use provided automated inspection equipment can meet the intent of a required visual inspection and automated testing equipment can produce the same action as required by the testing requirements. Beyond that there are a few other criteria specific to when automated inspection and testing is utilized such as where automated tests do not discharge water that at least once every 3 years the discharge must be visually observed. At that point it becomes a cost-benefit analysis for the stakeholders and primarily the building owner. Activities required at greater frequencies might present more of a benefit while those required less frequently might see less of a benefit. Let’s review the requirements specific to automated and remote inspections. To start, automated test devices must be listed for the purpose of the test being conducted if they are subjected to system pressure or are integral to the operation of the system during a fire event. The equipment must be such that its failure does not impair the operation of the system unless that failure can be indicated by a supervisory signal to the fire alarm system. Similarly, any failure of a component or system to pass an automated test must result in an audible supervisory signal and failure of automated inspection and testing equipment must result in a trouble signal. The monitoring and signals required ensure that instances where there are issues with the automated testing or inspection equipment or an unsatisfactory inspection or test result notification will be made and the situation can be remedied. The testing frequencies of NFPA 25 must be maintained regardless of the functionality of automated testing equipment and a record of all inspection and testing must be maintained in accordance with the requirements that apply to all inspection and testing. One of the benefits of automated inspection and testing is that there is not necessarily a need for personnel on site. However, certain circumstances might need to be addressed quickly. This is specified for no-flow testing of fire pumps. This testing is required on a weekly or monthly basis depending on the type of pump and the building it is located in.  The 2020 edition of NFPA 25 requires that when remotely monitored automated testing of the no-flow fire pump test is being performed qualified personnel must be able to respond to an abnormal condition within 5 minutes. In all reality, this means that a qualified person must be located on site. For the proposed 2023 edition which will be approved this summer that timeframe is to be changed to 4 hours. This additional time means that someone does not need to be immediately on site but can respond quickly enough to take the needed corrective action. The use of technologies to perform automated inspections and testing will only grow in future years. As it becomes more widely used, as building owners, service providers, and AHJs gain more experience, and the use expands into other areas of fire protection and life safety with the future publication of NFPA 915, it is very likely that the requirements will continue evolve
Frozen sprinkler

Dry Sprinklers

Dry sprinklers are a type of sprinkler that are able to extend into a cold space while holding the water back in a space that can be maintained at temperatures where freezing isn’t a concern. Although there are several other methods for installing sprinkler systems in areas subject to freezing, dry sprinklers allow a wet pipe system to be installed while also being able to protect ancillary areas that might be subject to freezing temperatures. Common examples of where you might see dry sprinklers installed include loading bays or balconies that are exposed to the outside ambient temperatures and refrigerated spaces like freezer rooms. Heat transfer basics When thinking about how a dry sprinkler works, we need to consider some heat transfer basics. First, heat always moves from warm to cold and heat transfer occurs in three different ways, conduction, convection and radiation. Below is a brief description of each. Conduction: Conduction is the transfer of energy within a solid, liquid or gas. In terms of dry sprinklers, this is when the cold air in the refrigerated space removes heat from the sprinkler which then removes heat from the piping. This transfer of heat from the sprinkler system into the refrigerated space is what causes the risk of water freezing within the sprinkler piping.    Convection: Convection is the transfer of energy between a solid surface and a moving fluid, such as air and water. This comes into play with sprinkler systems when sprinklers are installed outdoors or in other areas where it can be both cold and windy. Windy conditions increase the rate of heat transfer, meaning that the sprinkler piping looses heat to the outside air more quickly. This starts a chain reaction of heat transfer with the outside air cooling the sprinkler pipe and water inside the pipe located in the heated space loosing heat to the cold sprinkler pipe . If the wind speed increases so much that the sprinkler piping is losing heat faster than the indoor ambient air can provide heat then there is a risk of the water in the pipe freezing.     Radiation: Radiation is the exchange of energy through electromagnetic waves. Think of this as the sun heating up the interior of your car hotter than the outside air. That extra heat comes from radiation. This doesn’t often come into play when dealing with sprinkler systems, but if the sprinklers are in an area heated by the sun during the day, the risk of freezing may increase overnight when the sun goes down. How does a dry sprinkler work? Dry sprinklers work by preventing water from being within the part of the sprinkler piping that will be exposed to cold temperatures. If you are familiar with how a dry fire hydrant works, this is very similar to that.  Dry sprinklers include a portion of piping (often referred to as the barrel) where the water will be sealed off from until the heat element in the sprinkler operated and releases air which in turn releases the seal, allowing water to flow through the orifice of the sprinkler and impact the deflector to discharge on the fire.   Under certain ambient conditions, wet pipe systems having dry sprinklers can freeze due to heat loss by conduction. Therefore, due consideration should be given to the amount of heat maintained in the heated space, the length of the pipe in the heated space, the temperatures anticipated in the non-heated space and other relevant factors. Installation requirements for dry sprinklers Dry sprinklers must be long enough to avoid freezing the water-filled pipes due to conduction along the barrel. To ensure the barrel of the dry sprinkler is long enough NFPA 13 contains the following table in Chapter 15 (2022 edition) which gives the minimum exposed barrel length based off of the temperature that the discharge end of the sprinkler will be exposed to.    Dry sprinkler manufacturers have minimum required lengths to ensure that the dry sprinkler is properly installed and that the point of attachment to the wet pipe sprinkler system will be properly protected against condensation, freezing, and ice plugs. While dry sprinklers are available in many different lengths for various applications where used in conjunction with a wet pipe sprinkler system, care should be taken to ensure that the minimum required lengths are met based on the manufacturer’s recommendations and the expected exposed temperature. For example, in a freezer application, where the branch line can be located directly above the freezer, it might be necessary to elevate the branch line to ensure that the minimum distance is maintained between the cold region and the point of connection to the wet pipe system. It is the length of the barrel exposed to warm air that is important, not the overall length of the dry barrel sprinkler. Ultimately sprinkler systems can be configured in a number of different ways and it is the job of the engineer/designer is to try and make it as efficient as possible. Sometimes this means using dry sprinklers to prevent the water inside of the sprinkler piping from freezing but this isn’t the only method available. Other options include: Dry pipe sprinkler systems, Preaction sprinkler systems, Heat tracing on sprinkler pipe, Listed anti-freeze solution. Whatever method you are using, it is important to understand that there are options out there and that each one of those options has specific design criteria and unique installation requirements that need to be followed to meet the indented objectives. Dry sprinklers may be an effective way of achieving this for ancillary spaces included in a wet pipe system. For more information on the different types of sprinklers, sprinkler systems and other methods for protecting your sprinkler system from freezing check out the following blogs: Options for Installing Sprinklers in Areas Subject to Freezing Types of Sprinkler Systems Types of Sprinklers

Fire Fighter Safety Building Marking Systems

There are two main ways in which fire fighters currently receive information about fire protection features and construction types of a building they are responding to. The first is from a pre-incident plan (see NFPA 1620 for information about pre-incident planning) which is available as a result of prior building inspection and the second is through signage on the building. The most widely adopted signage which most fire fighters are familiar with is the NFPA 704 hazard diamond, which provides information about hazardous materials present and the fire, health, instability and special hazards which they pose. However, there is a lesser-known marking system that has been developed and incorporated in Appendix C of NFPA 1, which if utilized can provide fire fighters the basic information about fire protection features and building construction quickly and concisely as they’re arriving on scene of an emergency. Let’s look at why this type of marking system is important to fire fighters. Modern buildings are designed with fire protection features to protect both occupants and the building itself. Some of these features provide active protection, such as fire suppression systems, while others provide passive protection such as fire resistive construction. The required protection level is dictated by the codes incorporated by reference into law by the authority having jurisdiction at the time the building was designed and constructed, or under a retroactive requirement after the building is occupied. The specific fire protection features in a building, combined with the construction type will play a role in the tactical approaches to suppressing a fire in that building. So, having this information quickly and concisely displayed on the exterior of the building can enhance the fire department’s effectiveness. Although some states have adopted signs identifying construction type and location of truss construction, the fire fighter safety building marking system (FSBMS) in Appendix C of NFPA 1 goes further to include the hazard level of the contents, presence of fire sprinkler and standpipe systems, occupancy and life safety issues and other special designations. What does it look like?   The Maltese cross, which draws its origins from the Knights of Malta, has been widely adopted as a symbol of the fire service. The eight-pointed cross can be easily identified by its curved arcs between the points which all converge on a center circle. The FSBMS utilizes a rating system in each of the arms of the cross and the center circle to concisely display the hazard level, fire suppression systems, occupancy life safety issues and special hazards of a given building. The image above is an example of a FSBMS symbol. These signs should be located “in a position to be plainly legible and visible from the street or road fronting the property or as approved by the fire department.” To aide in visibility the signs should incorporate a white reflective background and black lettering.  Now let’s look at what each of the letters in the four sections of the cross identify. Rating System Construction Type The construction type is identified utilizing letter combinations in the top section of the Maltese cross as follows: FR — Fire-resistive construction NC — Noncombustible construction ORD — Ordinary construction HT — Heavy timber construction C — Combustible construction These construction types provide firefighters a general understanding of how well the building will resist collapse under fire conditions. Fire resistive construction would theoretically resist collapse the longest and combustible construction has the potential for the earliest collapse. Hazards of Contents The hazard of the building’s contents as it relates to fire conditions will be displayed on the left section of the Maltese cross as follows: L — Low hazard. Low hazard contents shall be classified as those of such low combustibility that no self-propagating fire therein can occur. M — Moderate hazard. Moderate hazard contents shall be classified as those that are likely to burn with moderate rapidity or to give off a considerable volume of smoke. H — High hazard. High hazard contents shall be classified as those that are likely to burn with extreme rapidity or from which explosions are likely. The hazard level will provide fire fighters with a general idea of how rapidly a fire will grow and spread through the building contents. This information can be used to anticipate the amount of water and firefighting resources needed to effectively control the fire. Automatic Fire Sprinkler and Standpipe System The presence of automatic fire sprinklers and standpipe systems will be displayed in the right section of the cross as follows: A — Automatic fire sprinkler system installed throughout P — Partial automatic fire sprinkler system or other suppression system installed S — Standpipe system installed N — None The general understanding of what active fire suppression systems are located in the building will guide firefighter’s tactics including apparatus positioning and hose line selection. Occupancy/Life Safety Issues The occupancy and life safety issues will be displayed in the lower section of the cross as follows: L — Business, industrial, mercantile, residential, and storage occupancies M — Ambulatory health care, assembly, educational, and day care occupancies H — Detention and correction facilities, health care, and board and care occupancies This information about building occupants/occupancy type will allow firefighters to gauge the difficulty in evacuating occupants from the building. The L occupancies representing those where the occupant load is lower, and occupants can most effectively evacuate unassisted. The M is of moderate concern where the occupant load is higher and/or the occupants may need additional assistance due to age or health conditions. The H is of high concern where the occupants may not be able to self-evacuate and considerable resources will be needed to evacuate the building. Special Hazards The center circle has been left empty to allow the inclusion of special hazards or provisions. This may be a location to include such things as truss type construction or even the hazardous materials information for example an NFPA 704 diamond, as long as the provisions for size of 704 are met. Summary Having the information on construction type, hazard level of contents, presence of sprinkler and standpipe systems and occupancy/life safety issues has the potential to enhance the effectiveness of firefighters arriving on scene. These responders would be equipped with the knowledge needed to best address an emergency in the building. States which have incorporated NFPA 1 into law should take the extra step to specifically name Annex C in the incorporating ordinance, thus incorporating a national standard the firefighter safety building marking system into law in their jurisdictions. Unless specifically incorporated by refence the FSBMS in Annex C would be a recommendation rather than a requirement. A national system has the potential to increase firefighter effectiveness while decreasing the number of fire fighter injuries and deaths by providing important information quickly and concisely as they arrive on scene. 

Fire Protection Research Foundation publishes “Firefighting Foams: Fire Service Roadmap” report

Fire incidents involving flammable liquids have historically resulted in dire consequences. Incidents can occur in aircraft hangars, shipboard spaces, flammable liquids fueling facilities, large fuel storage tanks, and other settings and can range from small, short spill fires to large tank farm fires which can burn for multiple days. A prominent example of the latter is the Intercontinental Terminals Company Deer Park petrochemical facility fire in Texas in March 2019. That fire started on March 17 and was finally brought under control on March 23. Class B firefighting foams are the primary agents used for the vapor suppression and extinguishment of flammable liquid fires in both manual and fixed system applications. Firefighting foams form a film and/or a blanket of bubbles on the surface of flammable liquids and prevent the fuel vapors and oxygen from interacting and creating a flammable mixture. For nearly five decades, Aqueous Film Forming Foams (AFFF) have been used as the dominant and effective Class B firefighting foam. Prior to the adoption of AFFF, the primary agent for flammable liquid firefighting was Protein Foams, which are derived from the hydrolysis of protein products and then delivered as aspirated foam to produce a smothering blanket of foam bubbles on the fuel surface. AFFF contains fluorosurfactants (per- and poly- fluoroalkyl substances [PFAS]) that provide the essential characteristics of fuel repellency, heat stability, low surface tension, and positive spreading coefficient so that an aqueous film formation can be formed on the fuel surface. AFFF has traditionally been recognized for its effective fire control characteristics. However, today these foams are now of significant concern in light of potential adverse health and environmental impact. The potential environmental, safety and occupational health risks associated with the use of fluorosurfactants such as some PFAS present in AFFFs started to become evident to the scientific community in the early 2000s. The unique chemical nature of the carbon-fluorine bond in PFAS make some of these compounds persistent, bio accumulative, toxic and have emerged as “contaminants of concern” as considered by the EPA. As a result, the ability to use AFFF to extinguish Class B fires continues to be greatly restricted due to bans in numerous States in the United States and in countries across the world such as Australia. Recently, Federal and State authorities have implemented health and environmental regulatory actions for PFAS and PFAS-containing AFFF. These regulations will ultimately impact, if not eliminate the production, distribution, and use of legacy AFFF in upcoming years. As more regulations come into place to address this issue, fire departments and other industrial end users are seeking AFFF replacements. In the meantime, the capabilities and limitations of the replacement foams and agents are continuing to be investigated through various research and testing programs to better understand their characteristics and effectiveness for various applications. The Fire Protection Research Foundation (FPRF), the research affiliate of NFPA, facilitated a research testing program (2018-20) to evaluate the fire protection performance and effectiveness of multiple fluorine free Class B firefighting foams on fires involving hydrocarbon and alcohol fuels. This study provided guidance to inform the foam system application standard, i.e., NFPA 11, Standard for Low−, Medium−, and High− Expansion Foam based on the testing conducted at the time of this research, and identified knowledge gaps and research needs so that we can better understand the capabilities and limitations of fluorine free foams. Additionally, there are multiple other ongoing research efforts. There are research programs led by the US Department of Defense’s SERDP and ESTCP underway, including  testing on the development of PFAS-free firefighting formulations, studying the fire suppression performance and ecotoxicology of these formulations as well as the cleaning technologies for firefighting equipment. LASTFIRE (Large Atmospheric Storage Tank Fires), an international industrial end user consortium, has also been focusing on the selection and use of firefighting foams for large storage tank applications. Additionally, the Firefighter Cancer Cohort Study is developing a national framework to collect and integrate firefighter epidemiologic surveys, biomarkers, and exposure data focused on carcinogenic exposures and health effects. Part of the long-term cohort study will look at the health effects of firefighters that have been routinely exposed to firefighting foams during their activities and careers. Clearly, this is a complex problem, with concerns that include fire control/extinguishing performance, health exposure, and environmental contamination. And for the fire service, challenging Class B flammable liquid fires are not going away and must be addressed. The learning from these ongoing studies have been promising and demonstrate a step in the right direction to develop a full understanding of this complex problem so that we can transition to firefighting foams of the future without experiencing “substitution regret” (i.e., to avoid multiple repeated replacements over time). The Fire Protection Research Foundation recently published the report titled “Firefighting Foams: Fire Service Roadmap.” This project was initiated with the funding support from FEMA Assistance to Firefighters Grant (AFG) program, with an overall goal to provide guidance to the fire service community by developing a roadmap to transition from AFFFs to a suitable, environmentally friendly, non-toxic, and effective alternative. The roadmap document is based on the information available at the time of the program. The roadmap and associated documentation have been assembled in a systematic path that covers current regulations, considerations for transitioning to replacement foam, cleaning of equipment and disposal of effluents and legacy concentrates, foam selection and implementation considerations, minimizing firefighter exposures, and ways to handle foam discharged from a cleanup and documentation perspective. A key element of this project entailed a three-day virtual workshop hosted by the FPRF late last year, October 2021. Subject matter experts delivered 28 presentations on the state of knowledge and related issues. If you missed this FPRF workshop, please visit the project website for workshop presentations, and final proceedings. Did you know the Research Foundation is celebrating its 40th year in existence in 2022? Learn more about this noteworthy milestone at www.nfpa.org/fprf40.

Water Mist Systems Overview

Water mist systems are fire suppression systems that use very small water droplets to extinguish or control fires. These droplets are effective at controlling fires while using less water and having smaller piping than a standard sprinkler system due to the increased cooling effects, oxygen displacement and pre-wetting that the droplet size and distribution provide. Some additional benefits of water mist fire protection systems include reduced water damage and low environmental impact, while one of the trade offs include higher system pressure. This blog will review some of the basics about these systems to help add these systems as an option in your fire protection design portfolio. The droplet size for water mist systems can vary between 1000 microns and 10 microns. This small droplet size decreases the required application rate, enhances evaporation, and helps reduce oxygen levels to extinguish visible and hidden fires. Water mist systems have been used for specific applications (such as maritime) for a long time but starting in the mid-1990’s advancement in the use of water mist systems was propelled by the phasing out of halon and their use as a fire safety system for spaces where the amount of water that can be stored or discharged is limited. In addition, there is a long list of applications in which water mist systems have been listed for use including the following: Machinery spaces Combustion turbines Industrial oil cookers Computer room raised floors Data processing equipment rooms Chemical fume hoods Continuous wood board presses Shipboard passenger cabins and corridors Shipboard accommodation and public space areas Road tunnels Cable conduit tunnels Application There are a few different ways to apply water mist fire protection systems in your building or facility. These types of system configurations will look similar to clean agent system applications because the two systems share several commonalities in how they protect against fires. Local Application – This configuration is used to protect a specific hazard or object. An example may be the protection of a piece of equipment in a large compartment. The system would be designed to discharge water mist directly onto the object. Total Compartment Application - This type of system provides protection to all fire hazards and all areas in a compartment. The open nozzles are positioned in a grid so that water mist discharges approximately uniformly throughout the entire volume. Zoned Application - This type of system is configured to discharge mist from portions of a larger system as required to control fire in a specific part of a compartment. It would be installed in circumstances where the water demand for a total compartment system (i.e., a deluge system), would be beyond the capability of the water supply. Zoning the water mist piping network, however, requires the installation of a detection system that can accurately find the location of a fire. Occupancy Protection Systems - A water mist system utilizing automatic water mist nozzles installed throughout a building or a portion of a building and intended to control, suppress, or extinguish a fire. Nozzle types There are several different types of nozzles that can be found in a water mist fire protection system. Automatic - Nozzles that operate independently of other nozzles by means of a detection/activation device built into the nozzle. This activation device is typically a heat responsive element or actuator. Nonautomatic - Nozzles that do not have individual actuators or heat-responsive elements. These types of nozzles are used in deluge systems where the nozzles are always open. Multifunctional - Nozzles capable of operation using both automatic and nonautomatic means. The actuation of a multifunctional water mist nozzle can be by a built-in detection and activation device and/or by an independent means of activation. Electronically-operated automatic - Nozzles that are normally closed and operated by electrical energy that is initiated and supplied by fire detection and control equipment. System types There are various types of water mist systems which are the same categories as the different types of sprinkler systems. Since we recently posted a blog covering the types of sprinkler systems that goes into the details about each type, I’m going to keep this section brief and just give a quick overview. Deluge System - A water mist system utilizing nonautomatic mist nozzles (open) attached to a piping network connected to the fluid supply(ies) directly or through a valve controlled by an independent detection system installed in the same area as the mist nozzles. Wet Pipe System - A water mist system using automatic nozzles attached to a piping system containing water and connected to a water supply so that water discharges immediately from nozzles operated by the heat from a fire. Pre-action Systems - A water mist system using automatic nozzles attached to a piping system that contains air that might or might not be under pressure, with a supplemental detection system installed in the same areas as the mist nozzles. The actuation of the detection system opens a valve that allows water to flow into the piping system and discharges through all opened nozzles in the system. Dry Pipe Systems - A water mist system using automatic nozzles attached to a piping system containing air, nitrogen, or inert gas under pressure, the release of which (as from an opening of an automatic nozzle) allows the water pressure to open a dry pipe valve. The water then flows into the piping system and out through any open nozzles. Droplet production methods Water mist fire protection systems have the option of being either a single fluid (water) or twin fluid (water & atomizing media) system. Single-Fluid - A single-fluid media system requires one set of distribution piping to transport the fluid to each nozzle. The droplets are then formed in one of the following ways: Liquid should be discharged at a high velocity with respect to the surrounding air. The difference in velocities between the liquid and surrounding air should shear the liquid into small droplets. A liquid stream is impinged upon a fixed surface. The impact of the liquid on the surface breaks the liquid stream into small droplets. Two liquid streams of similar composition collide with one another. The collision of the two streams breaks the individual streams into small droplets. Liquid is either vibrated or electrically broken into small droplets (ultrasonic and electrostatic atomizers). Liquid is heated above its boiling point in a pressure vessel and released suddenly to atmospheric pressure (flashing liquid sprays). Twin Fluid – Twin-fluid media systems produce water mist (droplet production) by impingement of two fluids delivered from separate piping systems. One set of piping provides a liquid (water) to the nozzle, and the second piping network provides an atomizing fluid/media. Both single-fluid and twin-fluid systems can be operated in the low, intermediate, or high pressure range, which is based on the greatest pressure that the distribution piping is exposed to, as shown in the table below.     Low Pressure System Intermediate Pressure System High Pressure System Imperial Units Under 175 psi 175 – 500 psi Over 500 psi Metric Units Under 12.1 bar 12.1 – 34.5 bar Over 34.5 bar Conclusion Ultimately, while water mist fire protection systems have not yet outpaced the prevalence of traditional sprinkler systems there are numerous benefits associated with them to justify their use in many applications. For information on the requirements associated with water mist systems please see NFPA 750, Standard on Water Mist Fire Protection Systems and for more information on the systems themselves check out the NFPA Fire Protection Handbook, Chapter 16-8.
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