AUTHOR: Brian O'Connor

An Overview of NFPA 110

Emergency power generators are an integral component in many fire and life safety systems. For this reason, NFPA 110, Standard for Emergency and Standby Power Systems, is referenced by many of the most widely used codes and standards. NFPA 110 addresses performance requirements for emergency and standby power systems. These systems provide an alternate source of electrical power in buildings when the normal electrical power source fails. Emergency power systems are made up of several components that need to work together to make sure electrical power is restored. These include power sources, transfer equipment, controls, supervisory equipment, and accessory equipment needed to supply electrical power to the selected circuits. This blog is meant to give an overview of the standard and its key chapters, but it’s not a replacement for reading and knowing the exact requirements of NFPA 110. What is an emergency and standby power system? In NFPA 110, there are two main terms used for emergency power or standby power. Those terms are emergency power supply and emergency power supply system. The emergency power supply is the source of the electrical power and includes everything necessary to generate the power. This includes the fuel supply (energy source), the equipment used to convert the fuel to electrical energy (energy converter), as well as the necessary accessories, such as the starting system and batteries. An emergency power supply system is a system that includes the emergency power supply as well as a system of conductors, disconnecting means, overcurrent protective devices, transfer switches, and all control, supervisory, and support devices up to and including the load terminals of the transfer equipment needed for the system to operate as a safe and reliable source of electric power. Chapter 4 ­– Classification of Emergency Power Supply Systems Emergency power supply systems are used in many different applications. Requirements that fit one situation might not be appropriate for another situation. When other codes or standards require an emergency power supply system, they typically call out the class, type, and level of system that is required. NFPA 110 contains the information for what these classes, types, and levels mean. Ultimately, these terms describe the capabilities of the system. Class – The class describes the minimum time that the emergency power supply system is designed to operate at its rated load without being refueled or recharged. It’s measured in hours, so a Class 0.25 needs to be able to provide power for 15 minutes and a Class 6 needs to provide power for 6 hours. The only class that falls outside of these rules is a Class X, which needs to provide power for “other time, in hours, as required by the application, code or user.” Type – The type describes the maximum time between when power is lost and when power is restored. This is measured in seconds, so a Type 10 needs to restore power within 10 seconds. There are two unique types that don’t follow this format. Type U, which needs to be basically uninterruptible—similar to an uninterruptible power supply system—and a Type M, which has no time limit and can be manually activated. Level – The level has to do with whether or not failure of the equipment could result in the loss of life or serious injury. It’s pretty straightforward. If failure of the equipment could result in the loss of life or serious injury. then it’s a Level 1. Otherwise, the emergency power supply system is a Level 2. The following table includes more information about classes, types, and levels. Chapter 5 – Emergency Power Supply: Energy Sources, Converters, and Accessories There are several different types of sources, or fuels, that can be used as an energy source, including liquified petroleum, liquified petroleum gas, natural gas, synthetic gas, and hydrogen gas. The most common is diesel fuel, which falls under the liquified petroleum category. Regardless of the type of fuel, it needs to be sized to 133 percent of the fuel required to run the generator for the time required by the class of the system. An energy source can’t do much without being converted into electrical energy. This can be done through a variety of means that are categorized into two groups: rotating equipment (generators) and fuel cells. Since reliability is one of the biggest concerns for an emergency power supply system, there are many requirements for equipment to be listed, designed, assembled, and tested to ensure it will function under emergency conditions. Chapter 6 – Transfer Switch Equipment A transfer switch does exactly what its name implies. It is a switch that, once activated, transfers the electrical load from one power source (normal power) to another (emergency power). They can be classified as an automatic transfer switch, a delayed automatic transfer switch, or a manual transfer switch, depending on the load being served and the required type of emergency power supply system. Automatic transfer switches, as well as delayed automatic, constantly monitor the source of normal power so, in the event of a power failure, the transfer switch moves the electrical load to the emergency power supply system. Chapter 6 of NFPA 110 contains performance requirements for transfer switches and their associated equipment. Chapter 7 – Installation and Environmental Considerations There are a lot of factors that can affect the performance of an emergency power supply system, one of which is the correct initial installation. Chapter 7 addresses the location and environmental considerations of installation that are essential for successful startup and performance, as well as safe operation and utilization of the emergency power supply system. This includes the following considerations: -        Location -        Lighting -        Mounting -        Vibration -        Noise -        HVAC -        Cooling system -        Fuel system -        Exhaust system -        Protection -        Distribution It is also crucial to know that the installed system will perform as expected without waiting for the initial operation to occur during the first power outage. Acceptance testing is required in order to confirm that the system will perform as required. Chapter 8 – Routine Maintenance and Operational Testing Emergency power supply systems are made of many components and subassemblies, all of which are required for reliable operation in order to provide emergency power in the event that primary power to a building is lost. The failure of one or more of these subsystems could compromise the ability of the emergency power system to deliver electricity in an emergency. For example, if the batteries in a diesel generator fail, then the entire system will not operate; in fact, battery failure is the most common cause of generator failure. Diligent maintenance of a building’s emergency power supply system, including routine inspections, system testing, and frequent maintenance, helps ensure proper operation. Some of the key considerations for the inspection, testing, and maintenance of emergency power supply systems are discussed in this blog. In general, the emergency power supply system needs to be inspected weekly, exercised monthly, and tested at least once every 36 months. NFPA 110 is a very commonly referenced standard and contains performance requirements for emergency power supply systems, most commonly generators. Hopefully this blog helped shed some light on the requirements and layout of the standard. For more information and training on NFPA 110, check out our online training as well as related certifications on the topic.

Fire Safety for Electric Vehicles and Other Modern Vehicles in Parking Structures

In spite of the global supply chain issues and loss of vehicles in the Felicity Ace cargo ship fire, the sales of electric vehicles (EVs) has been on the move, hitting 6.6 million in 2021, which is more than triple their market share from two years earlier. While this might be good news for our environment, it also brings unique fire challenges to both first responders and fire protection designers. The lithium-ion (or similar) batteries inside of these vehicles fail and burn in a much different way than internal combustion engine (ICE) vehicles. When lithium-ion batteries fail, they go through a process called thermal runaway, where a single cell failure can cause the production of heat and oxygen as well as flammable and toxic gasses. This then spreads to adjacent cells causing potential rapid fire growth or explosion. To give us some perspective about the size of this issue, it is estimated that there are around 16 million electric cars on the road worldwide, and studies have identified nearly 300 EV fires globally between 2010 and 2022. Compare this with ICE vehicle fires and we find that EV vehicle fires are less common of an occurrence, but more complicated of an event, since EVs fires can last longer and have the potential for electrical shock and reignition. While a majority of vehicle fires occur on the road, it’s the fires that occur in parking structures that lead to large economic loss as evidenced by recent fires at Liverpool’s Echo Arena (UK) and at the Stavanger Airport (Norway). What makes a parking garage or parking structure unique? Parking garages, often called parking structures in code books, are a unique type of occupancy. They can be located underground or above ground and are usually located in congested urban areas where large open parking lots aren’t feasible. They can be public or private and store anything from motorcycles and cars to trucks and buses. There might be access for each vehicle to enter and exit or there might be vehicles covering the entire floor area. RELATED: Read a 2019 NFPA Journal feature story about the risks introduced to parking garages by modern vehicles  There can also be several different types of technology integrated into parking structures, such as car stackers or automated parking systems which store and retrieve vehicles without a driver. These types of technologies increase the efficiency of the space being used but also increase the potential hazard by placing vehicles closer together. With all of these variables already existing in parking structures, the introduction of electric vehicles and electric vehicle charging stations adds more considerations that need to be made when designing and protecting these occupancies. What do the codes say? What do the current codes and standard say about electric vehicles in parking garages? While they don’t go into much detail, there are some requirements in NFPA 70®, National Electrical Code® (NEC®) and NFPA 88A, Standard for Parking Structures, that address certain safety concerns. The NEC is the go-to code when looking to protect people and property from electrical hazards and so, as appropriate, it has requirements for installing EV charging stations, or “Electric Vehicle Supply Equipment,” as they call it in the code. When conducting service load calculations, Article 220 requires EV Supply Equipment to be calculated at either 7,200 watts or the nameplate rating of the equipment, whichever is larger. This is to ensure the electrical supply will be able to handle the extra load put on by EVs charging. Most of the other requirements for electric vehicle charging stations are going to be located in Article 625, Electric Vehicle Power Transfer System. While this article contains many requirements, some of the highlights include requirements for EV charging equipment to be listed, to have a disconnecting means, and for charging coupling to be a minimum distance above the ground. The other major standard that addresses EVs in parking structures is NFPA 88A. Similar to NFPA 70, it requires the charging stations and equipment to be listed but it gives more details into the exact listing standards it needs to meet. -        Electric vehicle charging stations need to be listed to UL 2202, Standard for Electric Vehicle (EV) Charging System Equipment. -        Electric vehicle charging equipment need to be listed to UL 2594, Standard for Electric Vehicle Supply Equipment. -        Wireless power transfer equipment needs to be listed to UL 2750, UL LLC Outline of Investigation for Wireless Power Transfer Equipment for Electric Vehicles. Impact of modern vehicles The introduction of EVs into the ecosystem isn’t the only thing to consider when looking at how to properly design and protect parking structures. The fire characteristics of modern vehicles are also changing to include more plastics and other combustibles than ever before. While this benefits the fuel economy and lowers vehicle price, it increases the fuel load and fire growth we see in parking garages. A recent Fire Protection Research Foundation report dives into details about the fire hazard modern vehicles represent to parking garages and marine vessels. In addition, there have also been updates to various standards in response to these increased fire hazards found in parking garages.    The 2022 edition of NFPA 13, Standard for the Installation of Sprinkler Systems, for example, has changed to increase the recommended hazard classification for parking structures from an Ordinary Hazard Group 1 to an Ordinary Hazard Group 2. The effect is a 33 percent increase in the design density, moving from 0.15 gpm/ft2 to 0.2 gpm/ft2. As of January of 2021, FM Global data sheets have also increased the hazard category for parking garages and car parks from a Hazard Category 2 to a Hazard Category 3. New to the 2023 edition of NFPA 88A, all parking garages are now required to have sprinkler systems installed in accordance with NFPA 13. Prior to this edition, sprinklers didn’t have to be installed in open parking structures. Conclusion While technology is constantly evolving, so are NFPA codes, standards, trainings, research, and other resources. The ever-growing presence of lithium-ion batteries in our day-to-day lives are changing the fire characteristics of our built environment. Fire protection professionals need to be able to stay on top of these changes to ensure the safety of people and property. For more information on the resources NFPA provides relates to electric vehicles, check out nfpa.org/EV.
Fire extinguisher label

Fire Extinguisher Ratings

Fire extinguishers are often the first line of defense when it comes to stopping fires while they are still small. A key component of successfully using an extinguisher is ensuring the type of extinguisher is a match for the type of fire. There is the risk of spreading a fire if you use the wrong extinguisher, this is one of the reasons we only recommend that only those who are trained use extinguishers. This blog addresses how extinguishers are classified to help make the right decision when both installing and using portable fire extinguishers. Extinguishers are given a letter rating and some also have a number designation, which come from being tested to UL 711, Rating and Fire Testing of Fire Extinguishers. The letter on an extinguisher rating corresponds to the type of fire that extinguisher can put out while the number correlates to the extinguishing potential.  Class A Fires    Fires in ordinary combustible materials, such as wood, cloth, paper, rubber, and many plastics.  Class B Fires  Fires in flammable liquids, combustible liquids, petroleum greases, tars, oils, oil-based paints, solvents, lacquers, alcohols, and flammable gases.  Class C Fires  Fires that involve energized electrical equipment.  Class D Fires  Fires in combustible metals, such as magnesium, titanium, zirconium, sodium, lithium, and potassium.   Class K Fires  Fires in cooking appliances that involve combustible cooking media (vegetable or animal oils and fats).   Class A fires Class A fires are those that involve ordinary combustible materials such as wood, cloth, paper, rubber, and many plastics. So, when you see a fire extinguisher with a class A rating then you know it can safely put out a fire made of ordinary combustibles. This then leads to the question, well, what size fire extinguisher do I need. Class A fire extinguishers don’t exactly come in sizes, instead they are given a number designation that reflects the extinguishing potential. The higher the number the greater the extinguishing potential. Class A extinguishers need to be able to extinguish varying sizes of wood panels or wooden cribs in order to geta Class A rating. The wooden crib is made of 1 ½ in by 1 ½ in (38 mm by 38 mm) or 1 ½ in by 3 ½ in (38 mm by 89 mm) pieces of dry wood that vary in length depending on the number rating the manufacturer is going for. These pieces of wood are stacked into a crib, lit on fire and if the operator is successful in extinguishing the fire using the portable fire extinguisher, then it gets a certain number as well as the “A” rating. To give you a feeling for what these numbers actually mean; A 3-A rated extinguisher needs to put out a fire made of 144 pieces of 1 ½ in by 1 ½ in by 29 in wood. Class A extinguishers range from 1-A to 40-A Class B fires Extinguishers with a Class B rating are designed to be used on fires that involve flammable liquids and gases (think oil-based paint, alcohol, gasoline etc.). Class B rated extinguishers also have a number associated with them. That number is given to an extinguisher after it has been proven to be able to extinguish a certain size heptane fire. Heptane being one of the main components of gasoline. As an example of what exactly this means. A 10-B rated extinguisher has to be able to put out a fire consisting of 31 gallons of heptane in a 25 ft2 square steel pan. Class C fires Class C rated extinguishers can put out fires that involve energized electrical equipment. There are no numerical components for Class C ratings of extinguishers, we only care about the conductivity of the fire extinguisher. Basically, are you at risk of being shocked when using this extinguisher on energized equipment. To get the C rating the extinguishers are tested to see if any electrical current flows through them as they are discharged on energized electrical equipment. You won’t see an extinguisher with only a C rating, they will always have an A and/or B rating as well. (When electrical equipment is de-energized, extinguishers rated for Class A or B fires are used.) Class D fires Fires that involve combustible metals, such as magnesium, sodium, lithium, and potassium. There are no numbers associated with the Class D ratings of extinguishers. Extinguishers and agents for use on combustible metals fires are rated for the amount of agent and the method of application needed to control the fire. Class K fires Class K extinguishers are used on fires that involve cooking appliances that use cooking oils and fats (think deep fat fryer). There are no numerical components for Class K ratings because they are only tested on a single size fire source. This is tested by lighting a deep fat fryer fire and extinguishing it without any splashing of the oil or reignition. Fire extinguishers often can come with a combination of ratings, for example it’s pretty common to see an ABC rated fire extinguisher that is ok to use on ordinary combustibles, flammable liquids and energized electrical equipment. For more information on requirements related to portable fire extinguishers, check out NFPA 10, Standard for Portable Fire Extinguishers. Also, check out our other fire extinguisher related blogs: Fire Extinguisher Types Fire Extinguisher Placement Guide Fire Extinguisher Inspection Testing and Maintenance
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

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.

Clean Agent System Basics

Often times sprinkler systems are the required, go-to solution for protecting people and property against fire hazards. While they do an excellent job at this, sometime there is a need to quickly suppress a fire and protect high value sensitive items and this is where clean agents come into play, they have the ability to protect these assets by extinguishing fires without damaging equipment in the area. By definition a clean agent is a gaseous fire suppressant that is electrically nonconducting and that does not leave a residue upon evaporation. This is ideal when protecting high value items like historical artifacts or sensitive electronic equipment. The umbrella term “clean agents” includes both halocarbon agents and inert gas agents. Carbon dioxide (CO2) is another extinguishing agent with all the properties of a clean agent but is often classified differently due to the dangers associated with it. Here we will review the different types of gaseous fire protection systems and how they work. How do gaseous suppression agents work? Gaseous fire suppression agents work fundamentally the way any fire suppression media works; by removing one or more of the components of what was traditionally referred to as the fire triangle and now more appropriately, the fire tetrahedron. Unlike water, which primarily works by removing heat, most gaseous suppression systems suppress fire primarily by reducing the available oxygen for combustion with a secondary benefit of cooling and inhibiting the chemical chain reaction. A portion of the agents do have a primary mechanism of heat absorption with the secondary benefits being a reduced oxygen concentration and inhibiting the chemical chain reaction. Gaseous fire protection systems usually are supplied by pressurized gas or liquid cylinders. When this pressurized gas is released, it is volume expands and it goes through a process known as adiabatic cooling, which is the reduction of heat through change in air pressure caused by that volumetric expansion. This cooling is the primary mechanism by which heat is removed. These systems can provide protection through either a “total flooding” or a “local application” approach. Total flooding As the name suggests, total flooding systems discharge extinguishing agent throughout an entire space to suppress the fire. To do this, the gaseous agent must be introduced into the space and mix with the air in that space at a concentration that is specific to the particular gas chosen as well as the fuel class being protected. Specifics of this can be found in the standard related the appropriate type of agent. An important concept to understand when it comes to total flooding clean agent systems is that these extinguishing agents needs to reduce the oxygen available for combustion to below the threshold where it would occur and hold it there until the items involved cool below their auto ignition temperature. If the concentration were to disperse prior to the items cooling enough the fire could reignite. Since the agent needs to maintain a certain concentration for a period of time to suppress a fire it is important that the room air-tight enough to maintain concentrations for the minimum hold times. We have a great blog that dives further into this concept here. Local application As the name implies, local application systems discharge extinguishing agent, so the burning object is surrounded locally by a high concentration of agent to extinguish the fire. A local application system is often required because the enclosure itself is not suitable for a total flooding system. This means that when the protected object is not enclosed the discharge nozzles and rate of application must be capable of enveloping the object, which requires more agent to be discharged. The agent supply needs to be sufficient to maintain flow for the required time of protection, which is typically several minutes. Nozzle design is also critical, and the application design parameters must be determined by testing. Types of clean agents There are several distinct types of clean agents available, each with their own advantages, disadvantages, price points and design restrictions. The following are the main categories of clean agent types: Carbon Dioxide Even though NFPA does not classify it as one, Carbon Dioxide (CO2) can be considered the original clean agent. It works by both removing oxygen from the equation while simultaneously providing cooling to the fire. The biggest limitation when using this fire suppressant is that for it to be effective in extinguishing a fire it needs to displace oxygen at a level that is fatal for humans. For this reason, new CO2 systems are limited in their application and typically not permitted to be installed in normally occupied enclosures. More information on the specific requirements for the installation of CO2 systems can be found in the latest edition of NFPA 12, Standard on Carbon Dioxide Extinguishing Systems. Halocarbon agent Halocarbon agents are agents that contain as primary components one or more organic compounds containing one or more of the elements fluorine, chlorine, bromine, or iodine. Examples are hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs), perfluorocarbons (PFCs or FCs), fluoroiodocarbons (FICs), and fluoroketones (FKs). Halocarbons extinguish fires through a combination of chemical and physical mechanisms. Primarily they work by interrupting the chemical chain reaction of fire. Halocarbons also extract heat from the fire, reducing the flame temperature until it is below what is needed to maintain combustion. Oxygen depletion also plays a vital role in reducing flame temperature. Halocarbon Agents have been historically referred to as “Halon Replacement Agents” since they were developed to provide a more environmentally friendly alternative to Halon, which was an effective fire suppressant that is no longer produced. Halons have been identified as stratospheric ozone-depleting substances. In fact, halons have been identified as the most potent of all ozone-depleting substances. The Montreal Protocol on Substances That Deplete Stratospheric Ozone is an international agreement to control the production and trade of ozone-depleting substances. The agreement has been signed by over 140 countries and is administered by the United Nations Environment Program. Specific requirements for halocarbon agents can be found in NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems Inert gas An inert gas agent contains one or more of the following gases as components: helium, neon, argon, or nitrogen, and that can also contain carbon dioxide as a minor component. Unlike CO­2 inert gases are non-lethal to humans at low concentrations (although there is still always a concern when oxygen levels are low). Inert gases suppress fires primarily by reducing the oxygen concentration and reducing the flame temperature below what is required for combustion. While inert gases are an effective means of fire suppression, they are not as effective as halocarbon agents and require more agent to be dispersed to extinguish a fire. Like halocarbon agents, specific requirements for inert gas systems the can be found in NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems. Initiation & activation In the event of a fire clean agent systems are activated by a suppression releasing panel which detects the fire using automatic detection. Once a fire has been detected a releasing sequence starts often with a delay to allow occupants to evacuate. Notification appliances in the protected area sound for a pre-determined time before the system is activated. The gas is released from the cylinders by the releasing panel via an electronic signal to a solenoid valve on the agent tanks. The gas then flows through the piping and out the open nozzles to either protect a local area or flood the protected enclosure. A manual option of activation is also often required where the releasing panel receives the signal from a manual station. Should the activation be a false alarm, abort switches should be provided, which can stop the agent release during the pre-discharge phase. These clean agent systems are typically installed in addition to the sprinkler system but occasionally it might be able to replace a sprinkler system completely. For more details on when this might be possible check out this blog. Clean agent fire protection systems are a fantastic way to protect high value or sensitive electronic equipment. There are many options available between the inert gases, halocarbons and CO2 that vary in price, effectiveness, and design options. All these systems can be installed in either a total flooding or local application approach and have an involved process for activation and discharge. While these systems can have a high price point when compared to sprinklers, there will always be applications where these systems are needed.
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