AUTHOR: Brian O'Connor

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.

Hangers and Support of Sprinkler System Piping

With all of the hard work and effort that goes into designing and installing a sprinkler system, we want to make sure it’s going to stay in place for years to come. Designing the support of such a system is no easy task but if done right can help save lives and property. Hangers need to do three things:  connect to the building itself, typically to structural members; be long enough to reach the pipe they are supporting; and securely attach to the sprinkler system piping. Some hangers accomplish this with one piece while other types of hangers require multiple components. There are requirements for the specific hanger components, for example threaded rods, u-hooks and eye rods all need to be a certain thickness based on the size of the pipe they are supporting. Likewise, there are specific requirements on the type of fasteners that are based on the pipe size and material that the fasteners go into (wood, concrete or steel). This image shows a typical hanger assembly. It consists of a C-clamp that secures the threaded rod onto the building, the rod itself that reaches down to the pipe and the adjustable swivel ring that secures the rod to the pipe. As an added bonus there is a retainer strap that will help the C-clamp stay on the building in the event of an earthquake. This blog will address general requirements that cover most installations but it’s important to note that this blog doesn’t contain all of the requirements for hanging and bracing. To see all of the requirements for hanging and bracing be sure to read chapter 17 of NFPA 13. There are several different types of sprinkler piping support, this blog will discuss hangers (including trapeze hangers) pipe stands and riser clamps. Trapeze Hangers Trapeze hangers are a type of sprinkler piping support that consists of a length of pipe or angle iron that serves as a trapeze bar between multiple structural members which then support the sprinkler system piping. This is usually used for larger pipe so the load can be shared between two structural members or when you need to support pipe that is not directly underneath a structural member.  The requirements in NFPA 13 for trapeze give you a certain section modulus that the trapeze member needs to have, and this is based on the length of the trapeze and the size of the pipe it’s supporting. That section modulus is then translated into either a pipe or angle iron size that is needed for the trapeze member. Installation of Pipe Hangers Two main concepts to consider when it comes to the installation of pipe hangers is the location of hangers on branch lines and the maximum distance between hangers. Maximum distance between hangers needs to be in compliance with the table below. This is done to ensure that there are not long stretches of unsecured piping. Note that nonmetallic piping should follow the hanger spacing requirements located in the product listing. There is more to know about installing hangers than just placing them at their maximum intervals. The following requirements are in place to ensure hangers can properly support the sprinkler system before, during and after activation. Minimum number of hangers – there needs to be at least one hanger on each piece of pipe. Clearance to hangers – the distance between a hanger and an upright sprinkler needs to be at least 3 inches (75mm). This is done to prevent the hanger from becoming an obstruction to sprinkler discharge. Unsupported lengths – the maximum unsupported length between the end sprinkler and the last hanger in the line needs to comply with the table below. Keep in mind that there are different requirements for pendent sprinklers where the maximum static or flowing pressure exceeds 100 psi. Unsupported armover – the horizontal length of an unsupported armover can’t exceed 24 inches (600mm) for steel pipe and 12 in (300 mm) for copper tube. Once again, there are different requirements once the pressure exceeds 100 psi. Pipe Material Pipe Size Maximum Unsupported Length Steel 1 in (25 mm) 36 in (900 mm) 1 ¼ in (32 mm) 48 in (1200 mm) 1 ½ in (40 mm) or larger 60 (1500 mm) Copper 1 in (25 mm) 18 in (450 mm) 1 ¼ in (32 mm) 24 in (600 mm) 1 ½ in (40 mm) or larger 30 in (750 mm)   Support of Risers Risers, which are the vertical supply pipes in a sprinkler system, typically consist of large heavy pipes that are filled with a great deal of water. Due to the weight and force of water flowing through the piping, it is essential to be able to secure them from moving. Typically, risers are supported by a friction-type clamp that rests on or is secured to the floor slab. However, risers can also be supported with riser clamps that are fastened to the building structure or with hangers that support the horizontal piping at the top of the riser. When risers are installed in multistory buildings, they need to be supported at the lowest level and at each alternative level above that, as long as the distance between the supports doesn’t exceed 25 ft (7.6 m). Riser supports also need to be provided at the top of the riser as well as above and below offsets. Pipe Stands Sometimes it is impractical or infeasible to support sprinkler piping from the ceiling. When that is the case, pipe stands can be used to secure piping from the ground, for example, when supporting a back flow prevention device. When pipe stands are supporting piping from the ground, there are maximum heights in which the stands can support. The table below lists these limitations. Most pipe stands are much shorter and usually only used to support large pipe closer to the ground. When the system piping is 10 inch (250 mm) schedule 40 or smaller, it can be supported by a 2 inch (50 mm) schedule 40 pipe as long as the pipe stand isn’t any longer than 4ft (1.2m) (see figure below). The distance between pipe stands follows the same rules as the distance between hangers. Also, similar to pipe hangers it’s important to properly attach the pipe stand to the ground as well as attach the pipe stand to the system piping.   Performance Based Approach As an alternative to the prescriptive based requirements mentioned above you can follow the performance-based approach for installing hangers and pipe stands. With this method, hangers or pipe stands certified by a professional engineer to meet the five conditions listed below can be an acceptable alternative to the other requirements in the hanging and bracing chapter of NFPA 13. This approach is typically only used where listed hangers can not be used for a particular building arrangement or system configuration. Hangers need to be able to support five times the weight of the water filled pipe, plus 250 lbs (115kg) at each point of piping support. The points of support need to be able to support the system Hanger spacing needs to be in compliance with the table 17.4.2.1 (referenced earlier in the blog) Hanger components need to be either iron an iron alloy (such as steel) Engineering calculations need to be submitted to the AHJ as requested. Conclusion In addition to hangers, riser supports, pipe stands and other types of components that support the sprinklers against the pull of gravity, sprinkler systems sometimes also need to be able to be resistant to seismic activity.  Check out our recent blog for information on seismic protection of sprinkler systems. 

Types of Sprinklers

As the saying goes, you need the right tool for the right job, and this applies to selecting the right types of sprinklers to be used in a sprinkler system. This blog is designed to be a helpful reference and contains most of your sprinkler options along with a helpful description of each. While there are several different types of sprinklers, each sprinkler will have a characteristic related to their spray pattern, orientation, and response time that can vary and is addressed below. It is also important to note that although there are a wide variety of different nozzles that can be used as part of an NFPA 13 system this blog only addresses sprinklers. Before we jump into some of the varying characteristics of a sprinkle here is a quick note about basic sprinkler operation. A sprinkler works by having a heat-activated element made of either a glass bulb or a fusible metal link that will activate and discharge water when heated to a designated temperature. Sprinklers are tested and listed for specific uses, and they need to be used in accordance with their listing. SPRAY PATTERN When a sprinkler is activated, a plug is released, and water moves through an orifice at a certain flow and pressure. That water then collides with the deflector which is designed to create a certain spray pattern. Most sprinkler spray patterns fall into one of the following categories. Standard Spray Sprinklers. The standard spray sprinkler is installed in accordance with specific coverage area limitations and is available in pendent, upright, and sidewall configurations. Because the standard spray sprinkler is proven to be effective for a broad range of hazards and applications by adjusting the water discharge density, it is popular and, to a certain degree, serves as the benchmark for sprinkler measurement and performance. Extended Coverage Sprinklers. As the title suggests, these sprinklers have a larger, or extended, coverage area when they discharge. This can help save material and labor costs because you do not need to install as many sprinklers. The trade-off is that they might require a water supply with a higher pressure to discharge at the higher flow rate necessary to cover the larger area they were designed for. Extended coverage sprinklers also come in several orientations and response types. Old Type Sprinklers: Old style sprinklers are only permitted for special situations such as the protection of fur storage vaults. These sprinklers have a unique water distribution, where about half the water is directed upwards and half is directed down. This typically allows these sprinklers to be installed in either the pendent or upright position.   SPRINKLER ORIENTATIONS Sprinklers are designed to be installed in a certain orientation. While this allows additional design flexibility it is also important to ensure that sprinklers are installed in the orientation in which they are designed to be installed. Pendent Sprinkler: A sprinkler designed to be installed in such a way that the water stream is directed downward against the deflector. Pendent sprinklers are very common but standard pendent sprinklers can’t be used with dry pipe systems because water can get trapped between the sprinkler and branch line piping causing ice to block the flow of water. Upright Sprinkler: Upright sprinklers have a spray pattern that appears similar to that of a pendent sprinkler. The difference is that upright sprinklers are mounted to the top of branch lines or sprigs and installed in such a way that the water spray is directed upwards against the deflector. Upright sprinklers can be used in dry pipe systems because water can’t get trapped. Sidewall Sprinkler: Sidewall sprinklers typically are installed along a wall and discharge water away from the wall into the room or space. Sidewall sprinklers can be mounted on the side, bottom, or top of a branch line, as specified in their listings. The discharge pattern resembles one-quarter of a sphere, with a small portion of the discharge directed at the wall behind the sprinkler. Recessed Sprinkler: A sprinkler in which all or part of the body is mounted within a recessed housing. Some recessed sprinklers are meant to be partially recessed into a wall or ceiling while others are designed to be completely flush with the wall or ceiling. Only sprinklers designed and listed to be installed as a recessed sprinkler can be installed recessed. Concealed Sprinkler: A recessed sprinkler with cover plate. The cover plate is typically soldered to the frame that screws or pushes into the sprinkler assembly. The solder is designed to melt at a lower temperature than the sprinkler activation temperature. When the solder melts, the cover plate falls off allowing the sprinkler head deflector to drop below the ceiling height and distribute water after the sprinkler activates. SPRINKLER RESPONSE TYPES Sprinkler response types are determined by their Response Time Index (RTI). This is a method of measuring thermal sensitivity under standardized test conditions. In addition to sprinkler response time, sprinklers also can have different thermal elements that are designed to activate at varying temperatures. For more information on thermal characteristics of sprinkler check out our latest blog that covers that very topic. Quick Response (QR) Sprinkler: A type of spray sprinkler that has a thermal element with an RTI of 50 (meter-seconds)1⁄2 or less and is listed as a quick-response sprinkler for its intended use. A quick-response sprinkler is similar to a standard response sprinkler, except that it possesses a fast-response operating element, so when exposed to the same temperature change, a quick response sprinkler will operate faster than a standard response sprinkler. QR sprinkler technology was developed from residential sprinkler technology. QR sprinklers are tested against the same criteria as standard-response sprinklers. The difference in the size of the operating elements of QR sprinklers and standard-response sprinklers should be noted. Where glass bulbs are used for standard spray sprinklers, the diameter of the bulb of a QR sprinkler is typically less than that of a standard-response sprinkler. Where a metallic alloy is used, the operating heat responsive element of a standard-response sprinkler has more mass than the element used in a QR sprinkler. Standard Response Sprinkler: Sprinklers defined as standard response have a thermal element with an RTI of 80 (meters-seconds)1⁄2 or more. SPECIAL SPRINKLERS Residential Sprinkler: A type of fast-response sprinkler having a thermal element with an RTI of 50 (meters-seconds)1⁄2 or less that has been specifically investigated for its ability to enhance survivability in the room of fire origin and that is listed for use in the protection of dwelling units. Residential sprinklers are designed to prevent flashover, so the spray pattern throws water much higher. Residential sprinklers are required to pass wall wetting tests in addition to floor distribution. Dry Sprinkler: Sometimes referred to as dry barrel sprinklers, dry sprinklers are used in areas where the sprinklers and piping are subject to near-freezing temperatures such as freezers or balconies. A dry sprinkler or dry barrel sprinkler is a sprinkler that is secured in an extension nipple that has a seal at the inlet end to prevent water from entering the nipple until the sprinkler operates. Dry sprinklers are used so a wet pipe system can serve an area that is subject to freezing by holding the water back in a space that can be maintained above freezing. Open Sprinklers: Open sprinklers are used in deluge systems. They are not activated by individual thermal elements, instead the system water supply is held back by a deluge valve that is automatically opened (most often by activation of a heat detection system). This is meant to deliver a large amount of water over a specific area in a short amount of time. They are typically used for protection against high-hazard or rapidly spreading fires. Institutional Sprinkler: Installing sprinklers in a correctional or institutional facility can be tricky since they need to be tamper-proof. Institutional sprinklers are specially designed to prevent people from attaching anything to it that could inflict harm on themselves or others. They are also made with components that cannot be easily converted into makeshift weapons. Corrosion Resistant Sprinkler: A sprinkler fabricated with corrosion-resistant material, or with special coatings or platings, to be used in an atmosphere that would normally corrode sprinklers. Corrosion-resistant sprinklers are either covered with a decorative or corrosion-resistant coating or are designed for a specific function. Additional consideration of corrosion resistance should be given to any attached escutcheon. Stainless steel and aluminum escutcheons are often preferred over mild steel in harsh environments. STORAGE SPRINKLERS Most sprinklers are designed to control a fire. This means that they apply water to a fire to prevent it from growing out of control. This is done in order to allow the occupants to evacuate the building and firefighters to arrive and fully extinguish the fire. There is only one type of sprinkler that is designed to fully extinguish a fire. When it comes to the sprinklers used in the protection of storage areas you will notice that the names of the sprinklers indicate whether they control the fire (control mode) or suppress the fire (early suppression). Control Mode Density Area (CMDA): A type of spray sprinkler intended to provide fire control in storage applications using the density/area design criteria. Control Mode Specific Application (CMSA) These are designed for applications such as storage occupancies. These designs, along with most other types of sprinklers, are intended to control the fire, not suppress it. CMSA sprinklers are a type of spray sprinkler that can produce characteristic large water droplets and that is listed for its capability to provide fire control of specific high-challenge fire hazards. This term is meant to incorporate a wide variety of sprinklers capable of fire control in high challenge fire scenarios. Note that CMSA Sprinklers are tested for use in specific storage configurations and need to be used in accordance with their listing. You might hear some people refer to CMSA sprinklers as large-drop sprinklers. Early Suppression Fast Response (ESFR). Similar to CMSA sprinklers ESFR sprinklers are designed for storage occupancies. Although, ESFR sprinklers are designed for fire suppression rather than control. These are designed to protect rack storage without the need for in-rack sprinkler protection. The ESFR concept is to apply enough water to the burning fuel during the early phases of a fire and penetrate the developing fire plume, achieving suppression. ESFR sprinklers have a thermal element with an RTI of 50 (meters-seconds)1⁄2 or less and are listed for their capability to provide fire suppression of specific high-challenge fire hazards. Caution must be exercised to avoid confusing ESFR sprinklers with other types of sprinklers that are equipped with fast-response operating elements. A non-ESFR sprinkler with a fast-response element is not specifically designed to achieve fire suppression. The relationship among thermal sensitivity, actual delivered density, and required delivered density needs to be considered. Intermediate Level Sprinkler: A sprinkler equipped with integral shields to protect its operating elements from the discharge of sprinklers installed at higher elevations. Intermediate Level Sprinklers are typically designed for use in rack storage sprinkler systems where their thermal elements need to be shielded from the water spray of sprinklers above. Other applications where one might find Intermediate Level Sprinklers include areas beneath open gridded catwalks. RECENT TECHNOLOGY Here are some additional sprinkler types that have recently been brought to the market, they are not as common as some other types of sprinklers but it is important to be aware of them. Polymer sprinklers: A residential fire sprinkler comprised of mainly polymeric materials. These are typically slightly lighter than metallic sprinklers and are lead free, allowing them to be used in a system that uses potable water. As of the writing of this article these sprinklers are limited to being used in NFPA 13D systems. Electrically Operated Sprinklers: Electrically operated sprinklers are a technology in which the primary means of operation is through an electrical signal provided by an electronic control system using specialized detection and control algorithms. These systems are typically used in high challenge storage applications. The systems utilize a combination of heat and smoke detectors to pinpoint the precise location of a fire, which enables the system to actuate (open) the proper number of sprinklers to control and/or suppress the fire. If you enjoyed this blog be sure to check out our blog on the Thermal Characteristics of Sprinklers as well as our blog on the different Types of Sprinkler Systems. Important Notice: Any opinion expressed in this blog is the personal opinion of the author and does not necessarily represent the official position of NFPA or its Technical Committees. In addition, this piece is neither intended, nor should it be relied upon, to provide professional consultation or services.

Commodity Classifications in NFPA 13

Commodity classifications are used to categorize the contents of storage occupancies so that the appropriate sprinkler system design can be identified. Commodity classifications are determined by not only the product but also the packaging of that product, the container those packaged products are in, and even the pallet type. This can get a little complicated, so I’ll run through a quick example. We have glass jars stored in a double layered carboard box with cardboard dividers and it is sitting on a reinforced plastic pallet. Even though the glass jars are only a Class I commodity, the cardboard box and plastic pallet increases the fuel load so that it should be considered a Class IV. Commodity Classifications are broken down into Classes I through IV and Group A though C plastics with Class I being the lowest hazard level and Group A expanded plastics being the highest hazard level. Class I: A Class I commodity is defined as a noncombustible product that meets one of the following criteria: Placed directly on wood pallets Placed in single-layer corrugated cardboard boxes, with or without single-thickness cardboard dividers Shrink-wrapped or paper-wrapped as a unit load Class II: A Class II commodity is defined as a noncombustible product that is in slatted wooden crates, solid wood boxes, multiple-layered corrugated cardboard box, or equivalent combustible packaging material. Class III: A Class III commodity is defined as a product fashioned from wood, paper, natural fibers, or Group C plastics with or without cartons, boxes, or crates. A Class III commodity shall be permitted to contain a limited amount (5 percent or less by weight of nonexpanded plastic or 5 percent or less by volume of expanded plastic) of Group A or Group B plastics. Class IV: A Class IV commodity is defined as a product that meets one of the following criteria: Constructed partially or totally of Group B plastics Consists of free-flowing Group A plastic materials Cartoned, or within a wooden container, that contains greater than 5 percent and up to 15 percent by weight of Group A nonexpanded plastic Cartoned, or within a wooden container, that contains greater than 5 percent and up to 25 percent by volume of expanded Group A plastics Cartoned, or within a wooden container, that contains a mix of Group A expanded and nonexpanded plastics and complies with the graph section at the end of the blog Exposed, that contains greater than 5 percent and up to 15 percent by weight of Group A nonexpanded plastic Exposed, that contains a mix of Group A expanded and nonexpanded plastics and complies with the graph section at the end of the blog PLASTICS Plastics are a little more straightforward since there is a specific list of what each group contains. Classifying plastics gets complicated when the commodity being stored is a combination of different groups of plastics, but the graphs at the end of this blog should be able to help alleviate some of that work. Group C Plastics: Group C plastics are treated as Class III Commodities and consist of the following: Fluoroplastics (PCTFE — polychlorotrifluoroethylene; PTFE — polytetrafluoroethylene) Melamine (melamine formaldehyde) Phenolic PVC (polyvinyl chloride — flexible — PVCs with plasticizer content up to 20 percent) PVDC (polyvinylidene chloride) PVDF (polyvinylidene fluoride) Urea (urea formaldehyde) Group B Plastics: Group B plastics are treated as Class IV Commodities and consist of the following: Chloroprene rubber Fluoroplastics (ECTFE — ethylene-chlorotrifluoro-ethylene copolymer; ETFE — ethylene-tetrafluoroethylene-copolymer; FEP — fluorinated ethylene-propylene copolymer) Silicone rubber Group A Plastic: Group A plastics are further subdivided into expanded and nonexpanded Group A plastics and consist of all of the plastics listed in the table below. ABS (acrylonitrile-butadiene-styrene copolymer) FRP (fiberglass-reinforced polyester) Polycarbonate PVC (polyvinyl chloride — highly plasticized, with plasticizer content greater than 20 percent) (rarely found) Acetal (polyformaldehyde) Natural rubber Polyester elastomer Acrylic (polymethyl methacrylate) Nitrile-rubber (acrylonitrile-butadiene-rubber) Polyethylene Butyl rubber Nylon (nylon 6, nylon 6/6) Polypropylene PVF (polyvinyl fluoride) Cellulosics (cellulose acetate, cellulose acetate butyrate, ethyl cellulose) PET (thermoplastic polyester) Polystyrene SAN (styrene acrylonitrile) EPDM (ethylene-propylene rubber) Polybutadiene Polyurethane SBR (styrene-butadiene rubber) HELPFUL DEFINITIONS One of the biggest issues I see when people are starting to learn about sprinkler design for storage occupancies is that they don’t know the terminology. It is important to fully understand the definitions for the terms used in the storage chapters of NFPA 13, Standard for the Installation of Sprinkler Systems. I recommend looking at the definition chapter of NFPA 13 to make sure you understand exactly what a term means because oftentimes it means something different than what you would expect. Here are a couple of definitions that are important to understanding this blog. Expanded Group A Plastics: Those plastics, the density of which is reduced by the presence of air pockets dispersed throughout their mass. Some examples include packing peanuts or acoustic foam. Nonexpanded is everything else that is not covered under the definition of expanded. Free Flowing Group A Plastics (protect as Class IV): Those plastics that fall out of their containers during a fire, fill flue spaces, and create a smothering effect on the fire. Examples include powder, pellets, flakes or random-packed small objects. Free flowing plastics are those small objects that fill a box or a subdivision within the box without restraint. The theory is that during a fire. The objects will freely fall out of the box and either smother the fire or fall away from it, removing themselves as fuel. Since the burning rate is reduced and fuel load has been lessened, free-flowing plastics are permitted to be treated as a Class IV commodity. Exposed: Commodities not in packaging or coverings that absorb water. For example, a cardboard box or wooden container can both absorb water so they would not be considered exposed. However, something that is wrapped in plastic sheeting could be considered exposed since plastic sheeting doesn’t absorb water. Cartoned - A method of storage consisting of corrugated cardboard or paperboard containers fully enclosing the commodity. GRAPHS The following tables come from NFPA 13 to help with navigating how a commodity should be classified when it contains Group A plastics. Note that the X axis is percentage by volume while the Y axis is percentage be weight.  The first graph addresses exposed commodities while the second graph addresses commodities that are cartoned or within a wooden container (non-exposed). PALLETS When commodities are tested, they are tested on wooden pallets. This means that wooden pallets are assumed to be used in commodity classifications, however if plastic pallets are used, they increase the commodity classification by two classes. Although, if the plastic pallet is made of polypropylene or high-density polyethylene and marked as “nonreinforced” then the commodity classification only needs to be increased by one classification. Plastic Pallet Increase (+2) Class I --> Class III Class II --> Class IV Class III --> Group A Plastics Class IV --> Cartoned nonexpanded Group A plastic Group A Plastics --> Group A Plastics (No increase)  Unreinforced Polypropylene or High-Density Polyethylene Plastic Pallet Increase (+1) Class I --> Class II Class II --> Class III Class III --> Class IV Class IV --> Cartoned nonexpanded Group A plastic Group A Plastics --> Group A Plastics (No increase) Determining the classification for commodities in storage occupancies can get complicated at times but I can not stress how important of a step this is during the sprinkler design process. It is also imperative that the owner understands what the building is designed to handle as well as what can and can not be stored in the facility once it is built. I hope you enjoyed the blog. Comment below if you have questions and be sure to share this with friends and colleagues who might find it helpful.
Energy Storage System

Battery Energy Storage Hazards and Failure Modes

Around the globe energy storage systems are being installed at an unprecedented rate, and for good reasons. There are a lot of benefits that energy storage systems (ESS) can provide, but along with those benefits come some hazards that need to be considered. This blog will talk about a handful of hazards that are unique to energy storage systems as well as the failure modes that can lead to those hazards. While there are many different types of energy storage systems in existence, this blog will focus on the lithium-ion family of battery energy storage systems. The size of a battery ESS can also vary greatly but these hazards and failure modes apply to all battery ESS regardless of size. HAZARDS As with most electrical equipment there are common hazards that need to be addressed as part of operation and maintenance such as a potential for electrical shock and arc flash. These should always be accounted for when working in and around energy storage systems. More information on how to work with electrical equipment safely can be found in NFPA 70E, Standard for Electrical Safety in the Workplace. Thermal Runaway – Thermal runaway is the uncontrollable self-heating of a battery cell. It begins when the heat generated within a battery exceeds the amount of heat that can be dissipated to its surroundings. The initial overheated cell then generates flammable and toxic gasses and can reach a heat high enough to ignite those gasses. This phenomenon can cascade to adjacent cells and progress through the ESS, thus the term “runaway”. Off Gassing – The gasses that ae released from battery energy storage systems are highly flammable and toxic. The type of gas released depends on the battery chemistry involved but typically includes gases such as: carbon monoxide, carbon dioxide, hydrogen, methane, ethane, and other hydrocarbons. If the gas is able to reach it’s lower explosive limit before finding an ignition source then there is the potential for an explosion. An example of this occurred in Surprise, Arizona back in 2019. Stranded Energy – Standard energy is the term used for when a battery has no safe way of discharging its stored energy. This commonly occurs after an ESS fire has been extinguished and the battery terminals have been damaged. This is a shock hazard to those working with the damaged ESS since it still contains an unknown amount of electrical energy. Stranded energy can also lead to reignition of a fire within minute, hours, or even days after the initial event. FAILURE MODES There are several ways in which batteries can fail, often resulting in fires, explosions and/or the release of toxic gases. Thermal Abuse – Energy storage systems have a set range of temperatures in which they are designed to operate, which is usually provided by the manufacturer. If operating outside an acceptable temperature range, the ESS may not work as intended, may result in premature aging of the battery, and can even cause a complete failure that can lead to fire and explosions. Thermal abuse is caused by external sources, it is the result of contact with burning or overheated adjacent cells, elevated temperatures, or exposure to other external heat sources associated with both storage of the cells or the environment in which the ESS is installed. Electrical Abuse – Electrical abuse takes place when a battery is overcharged, charged too rapidly, or externally short-circuited. This can also occur if the battery is discharged too rapidly or if the battery is over discharged below its specified end voltage. Electrical abuse can lead to an inoperable ESS, overheating, fire, and explosion. Mechanical Abuse – Mechanical abuse occurs if the battery is physically compromised when the battery is crushed, dropped, penetrated, or otherwise distorted to failure by mechanical force. Internal Faults – Internal faults can result from inadequate design, the use of low-quality materials, or deficiencies in the manufacturing process. It might be worth noting that the failure rate for lithium-ion cells is said to be on the order of one in a million. Environmental Impacts – Environmental impacts can lead to battery failure. This can be the result of ambient temperature extremes, seismic activity, floods, ingress of debris or corrosive mists such as dust (deserts) or salt fog (marine locations), or rodent damage to wiring.  Some locations subjected to rapid temperature variations such as in the mountains can experience dewing leading to damage within the ESS located outdoors if not well-controlled. While there are numerous applications and advantages to using battery energy storage systems it is important to keep in mind that there are hazards associated with these installations. Understanding the hazards and what leads to those hazards is just the first step in protecting against them. Strategies to mitigate these hazards and failure modes can be found in NFPA 855, Standard for the installation of Energy Storage Systems. NFPA also has a number of other energy storage system resources including the following: Fact sheet on ESS PV and ESS training ESS resource page Blog on residential ESS
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