AUTHOR: Brian O'Connor

Explosions, Deflagrations, and Detonations

When it comes to things that go boom, terms such as explosion, deflagration, and detonation are often incorrectly used interchangeably. To help clear things up, this blog will go into the technical definitions of explosions, deflagrations, and detonations, as well as the appropriate time to use each term. Explosion An explosion is a sudden, rapid release of energy that produces potentially damaging pressures. When a gaseous fuel fills a space, it needs to mix to a certain air-fuel concentration to create an explosive atmosphere. When an ignition source is introduced into the explosive atmosphere, it creates a flame that travels away from the ignition site and expands the burned gases behind the flame front. When an explosion is confined, it creates a restraint of the expanding gases and results in an increased pressure within the enclosure. When the enclosure ruptures, this is what most people think of when they hear the term explosion. However, explosions don’t always need to be confined. The flame speed in explosions can be quick enough to produce compression waves and cause damage with little or no confinement. The damage potential of an explosion depends on the pressure that is created from the explosion as well as how quickly energy is released from the explosion. Explosions can be either detonations or deflagrations depending on their flame speed.   Explosion A sudden, rapid release of energy that produces potentially damaging pressures. Deflagrations and detonations are types of explosions.   Deflagration A deflagration is an explosion where the flame speed is lower than the speed of sound, which is approximately equal to 335 m/sec (750 mph). Explosives that deflagrate are known as low explosives. The actual speed of the explosion can vary from 1–350 m/s (2–780 mph). Peak pressures produced by low explosives are orders of magnitude lower than those produced by high explosives, and the damage inflicted by low explosives can vary greatly depending on the fuel and confinement. For example, if black powder is ignited outside of containment, it just fizzles, but when it is confined, it creates an explosion that can propel bullets.   Deflagration  An explosion where the flame front travels through the air-fuel mixture slower than the speed of sound   In addition to the black powder example, examples of deflagrations involving low explosives include the ignition of propane gas for a cooking grill and fuel powering of a combustion engine in a car.   Detonation A detonation is an explosion where the flame speed is greater than the speed of sound. Detonations are louder and often more destructive than deflagrations. While deflagration occurs when a fuel and oxidizer (typically air) mix, a detonation doesn’t always need an external oxidizer. Explosives that detonate are referred to as high explosives and have a detonation speed in the range of 2,000–8,200 m/sec (4,500–18,000 mph). High explosives are typically designed to cause destruction—often for demolition, mining, or warfare.   Detonation  An explosion where the flame front travels through the air-fuel mixture faster than the speed of sound   Examples of high explosives that detonate include dynamite, TNT, and C4, a plastic-based explosive.   Learn more Hopefully, this blog helped shed some light on these common terms you hear when discussing types of explosions. For more information on explosions, check out the 21st edition of the NFPA Fire Protection Handbook®, which contains several chapters on the topic, including Chapter 2-8, “Explosions,” Chapter 6-16, “Explosives and Blasting Agents,” Chapter 17-8, “Explosion Prevention and Protection,” and Chapter 18-6, “Deflagration Venting.” The following codes and standards are also related to explosions: NFPA 495, Explosive Materials Code NFPA 69, Standard on Explosion Prevention Systems NFPA 68, Standard on Explosion Protection by Deflagration Venting NFPA 67, Guide on Explosion Protection for Gaseous Mixtures in Pipe Systems If you want to learn more about a specific type of explosion—a dust explosion—check out the following Learn Something New™ video by NFPA Journal®.

Mobile Energy Storage Systems

Mobile energy storage systems are being deployed in jurisdictions around the world, and—as demonstrated by a 2023 New Year’s Day mobile energy storage system fire—accidents can happen. We want to make sure communities are prepared for when these systems are deployed in their backyard. This blog will outline key considerations for mobile energy storage systems. To see the full requirements, check out the latest edition of NFPA 855, Standard for the Installation of Stationary Energy Storage Systems. What is a mobile energy storage system?   An energy storage system (ESS) is a group of devices assembled together that is capable of storing energy in order to supply electrical energy at a later time. A mobile energy storage system is one of these systems that is capable of being moved and typically utilized as a temporary source of electrical power. In practice, this is often a battery storage array about the size of a semi-trailer. Mobile energy storage systems can be deployed to provide backup power for emergencies or to supplement electric vehicle charging stations during high demand, or used for any other application where electrical power is needed. While there are various types of ESS and many battery technologies, this blog will focus on the most prevalent type—lithium-ion battery energy storage systems. Many of these requirements apply to any type of mobile energy storage system; see NFPA 855 requirements for details on other technologies. When does NFPA 855 apply to mobile energy storage systems? The scope of NFPA 855 states that it applies to “mobile and portable energy storage systems installed in a stationary situation.” It also goes on to mention that the storage of lithium-ion batteries is included in the scope of the document. The application section then limits the application of the standard to certain-sized mobile energy storage systems. For all types of lithium-ion batteries, the threshold is 20 kWh (72 MJ) before the requirements of NFPA 855 apply. For batteries in one- and two-family dwellings and townhouse units, that threshold is reduced to 1 kWh (3.6 MJ). For more information on residential ESS requirements, check out our previous blog on that topic. When looking at how a mobile energy storage system works, we break its use down into three phases: the charging and storage phase, the in-transit phase, and the deployed stage. This is how I’ll break down the requirements as well. Charging and storage When charging and storing a mobile energy storage system, the requirements are relatively straightforward. The system should be treated as a stationary system as far as the requirements of NFPA 855 go. These requirements will vary based on whether the system is being stored indoors, outdoors, on a rooftop, or in a parking garage. In-transit While a mobile energy storage system is in transit from its normal charging and storage location to its deployment location, it typically travels on roads that are governed by the governmental transportation authority (in the US, that would the Department of Transportation). However, when the mobile energy storage system needs to be parked for more than an hour, it needs to be parked more than 100 ft (30.5 m) away from any occupied building, unless the authority having jurisdiction (AHJ) approves an alternative in advance.  Deployment documents Before a mobile energy storage system is deployed, it needs to be approved by the AHJ, and a permit must be obtained for the specific use case. The permit application must include the following items: Mobile Energy Storage System Permit Application Checklist o Information for the mobile energy storage system equipment and protection measures in the construction documents o Location and layout diagram of the area in which the mobile energy storage system is to be deployed, including a scale diagram of all nearby exposures o Location and content of signage o Description of fencing to be provided around the energy storage system and locking methods o Details on fire protection systems o The intended duration of operation, including connection and disconnection times and dates o Description of the temporary wiring, including connection methods, conductor type and size, and circuit overcurrent protection to be provided o Description how fire suppression system supply connections (water or another extinguishing agent) o Maintenance, service, and emergency response contact information. Deployed There are restrictions on where mobile energy storage systems can be deployed. For example, they are not allowed to be deployed indoors, in covered parking garages, on rooftops, below grade, or under building overhangs. There is also a restriction on how long mobile energy storage systems can be deployed before they need to be treated as a permanent energy storage system installation, and that threshold is 30 days. Additional limitations for where a mobile energy storage system can be deployed include a 10 ft (3 m) limitation on how close it can be to various exposures and a 50 ft (15.3 m) limitation on how close it can be to specific structures with an occupant load of 30 or greater. See NFPA 855 or the image above for more details on the exposures and occupancies. An energy storage system contains a large amount of energy stored in a small space, which may make it the target for those who look to cause harm. For this reason, a deployed mobile energy storage system is required to be provided with a fence with a locked gate that keeps the public at least 5 ft (1.5 m) away from the ESS. Conclusion There are many applications where mobile energy storage systems can play a pivotal role in helping deliver electricity to where it is needed. While this technology has great practical applications and even more potential, it’s important to recognize that it also brings unique hazards. Adherence to the requirements of NFPA 855 can help keep our communities safe while embracing current technology. Here are some additional NFPA® resources related to ESS safety: -       Energy storage system landing page -       Energy Storage and Solar Systems Safety Online Training -       Energy Storage Systems Safety Fact Sheet

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
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
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