AUTHOR: Shawn Mahoney

Fire Alarm Notification Delay from Sprinkler Waterflow

Over the past several months, I have noticed a few incidents occurring in mercantile occupancies that have raised some questions related to the allowable delay between sprinkler activation and fire alarm notification in the event of a fire, which is governed by NFPA 72®, National Fire Alarm and Signaling Code®. One example is a video of this fire in a Maryland Walmart. The video was taken by an occupant inside the building as they are exiting the building and shows sprinklers operating and controlling the fire. You notice that there is a time delay between the activation of the sprinklers and the activation of the occupant notification within the building. Many people are asking the question, why doesn’t the fire alarm immediately warn the occupants that there is a fire in the building as soon as the sprinklers activate? The answer is that NFPA 72 permits up to a 100-second delay between sprinkler waterflow and occupant notification, as you can see at the end of the video, the fire alarm did activate the occupant notification via audible and visual notification. The allowance for a 100-second delay before the actuation of alarm notification appliances is broken down into two requirements. The first requirement is related to the waterflow initiating device and found in section 17.13 of the 2022 edition of NFPA 72. 17.13.2 requires that the waterflow initiating device activate within 90 seconds after a flow occurs that is equal to or greater than the flow from a single sprinkler of the smallest orifice size. The 90-second allowance exists to reduce the number of nuisance alarms caused by water flow that can occur from pressure surges in the water supply system and allows time for the flow from a sprinkler in the system to be detected at the riser. The delay provides added assurance that the water flow in the sprinkler piping is in fact sustained flow from a sprinkler, and not just the result in a change in pressure. The reduction of nuisance alarms is important because a fire alarm system that has many nuisance alarms can cause the occupants to become complacent and may begin to ignore the fire alarm. This delay in the water flow switch activation can be created within the flow switch itself using a retard dial, or it can be accomplished with the use of a retarding device such as a retard chamber when using a pressure switch that is connected to the alarm port on a sprinkler system alarm valve. The second part of this delay is found within section 10.11.1. This section requires that the actuation of alarm notification appliances at the protected premises occurs within 10 seconds after the activation of the initiating device. This requirement exists to ensure that the operation of the notification appliances occurs within a timely manner after a fire has been detected. Between those two requirements in section 17.13.2 and 10.11.1, NFPA 72 permits up to a 100-second delay between the initial waterflow from a sprinkler and the actuation of the notification appliances within the building. In addition to this allowance intended to reduce the number of nuisance alarms, allowances exist to delay the actuation of notification appliances for other initiating devices with the use of a presignal feature or positive alarm sequence, though both require a detailed response plan and approval from the authority having jurisdiction. The next time someone asks you a question about the timing of sprinkler waterflow and fire alarm notification, remember that NFPA 72 permits the delay in the actuation of fire alarm notification appliances. This timing is engineered into the operation of the systems, and it exists to ensure that they function as effectively as possible and reduce unwanted nuisance alarms.
Atrium

Atrium Design Considerations

The use of vertical openings within buildings is a common design feature. Large spaces, typically in the center of a building, created by vertical openings through floors and ceilings are commonly referred to by architects as an atrium. Atriums are desirable to some building designs because they allow for light and ventilation within a space and allow for many parts of a building to feel connected with each other. However, atriums and other vertical openings pose some unique fire protection and life safety hazards that must be considered such as limiting the spread of fire and the products of combustion throughout the building. The base requirement in NFPA 101, The Life Safety Code, states that every floor that separates stories of a building must be constructed as a smoke barrier. If there are openings in the floor, these openings must be enclosed with fire barrier walls that extend from floor to floor or floor to roof. These two main base requirements apply to all occupancies unless a specific occupancy chapter provides an alternative option. This base requirement of separating stories exists to minimize the number of occupants that are exposed to the effects of a fire. There are exceptions that permit unprotected openings within floors that separate stories. The following protection packages are outlined in NFPA 101 and are permitted to be used under certain conditions: communicating space atrium partially enclosed two-story opening convenience opening When selecting an unprotected vertical opening protection package, the first thing to consider is the number of stories that are open to each other. If the opening connects three stories or fewer, then you will need to look and see if you can meet the requirements of a communicating space or convenience stair opening, if the opening connects 4 stories, then the space will need to meet the requirements for an atrium or convenience stair. If more than 4 stories are connected, then the requirements for an atrium will need to be met. For a deeper dive into types of vertical openings take a look at this blog. Let’s assume that the vertical openings within the building need to be protected as an atrium. Section 8.6.7 of NFPA 101 provides the requirements for an atrium, which include: an engineering analysis for smoke layer development separation from other spaces exit access requirements permissible contents sprinkler protection and if provided, requirements for a smoke control system (smoke management system) In this blog I am going to focus on the engineering analysis for smoke layer development and separation requirements. Where atriums are used, there is a need to minimize the risk of occupants on other floors being exposed to untenable conditions, such as low visibility, heat, and dangerous concentrations of smoke and toxic gases. To ensure that occupants are afforded tenable conditions, an engineering analysis must be completed to confirm that the smoke layer will stay at least 6 ft (1830 mm) above the highest walking surface within the atrium space for a period that is equal to 1.5 times the calculated egress time, or 20 minutes, whichever is greater.  It should be noted that the requirement for an engineering analysis does not mean that a smoke control or smoke management system is required in all atriums because there are cases in which tenable conditions can be maintained without a smoke management system. The engineering analysis should include the following elements: Fire dynamics, including the following: Fire size and location Materials likely to be burning Fire plume geometry Fire plume or smoke layer impact on means of egress Tenability conditions during the period of occupant egress Response and performance of building systems, including passive barriers, automatic detection and extinguishing, and smoke control Response time required for building occupants to reach building exits, including any time required to exit through the atrium as permitted in NFPA 101. If the engineering analysis shows that a smoke control system (smoke management system) is required in the atrium to keep the smoke layer at least 6 ft (1830 mm) above the highest walking surface then the system will need to be designed and installed in accordance with NFPA 92, Standard for Smoke Control Systems. NFPA 92 allows for different design approaches to smoke management including natural smoke filling, mechanical smoke exhaust, gravity smoke venting, and opposed flow to prevent smoke movement. For more information on smoke control systems take a look at this blog. To protect the occupants in adjacent portions of the building, NFPA 101 requires that atriums be separated from adjacent spaces using one of the following methods: Fire barriers with not less than a 1-hour fire resistance rating. Any number of levels are permitted to be open directly to the atrium based on the results of the engineering analysis. Glass walls and inoperable windows can serve as the separation provided they are protected with closely spaced sprinklers on either side of the glass. Want to learn more about atrium design? Want to see all the referenced requirements within the codes and standards? Take a look at our atrium design situation in the DiRECT feature on NFPA LiNK. This situation goes into more detail on design requirements as well as sprinkler system and fire alarm system design considerations. For more information on how to access NFPA LiNK with a 14-day free trial on your computer or mobile device go here.
Fire Hydrant

Calculating the Required Fire Flow

Providing water to the responding fire department is a crucial aspect of the overall fire protection and life safety strategy of an entire community. When a new building is developed or an existing building is renovated, it is important to make sure that the proper amount of water is available to the responding fire department to allow for both suppression of the fire in the building, and protection of any exposed buildings. Because of this, NFPA 1, The Fire Code, requires a minimum amount of water be provided based on the type of construction of the building as well as fire flow area. Fire flow is defined as the flow rate of a water supply, measured at 20 psi (137.9 kPa) residual pressure, that is available for the responding fire department for manual firefighting, typically this is water that is available at the surrounding fire hydrants, but it can be supplied with another approved source such as a static water supply like a tank or pond, or even using a fire department tanker shuttle service. In addition to using the required fire flow water supply for manual suppression of the fire with hose lines, when responding to a fire at a sprinklered building or a building that contains a standpipe system, the fire department will also connect their pumper up to these systems through a fire department connection to use their pumper and the available fire flow water supply to supplement the water supply of these systems. There is a difference between the required fire flow in NFPA 1 and the hose stream allowance that is required in NFPA 13, Standard for the Installation of Sprinkler Systems, to be added to the required sprinkler demand. The fire flow required by NFPA 1 is being provided for the fire department for both protection of exposures as well as the water required for manual suppression, while the hose stream allowance in NFPA 13 that is added to a sprinkler system demand is adding a safety factor to the calculations to account for the fact that the fire department will likely also be using water from the same water supply that the sprinkler system is being fed from, which will reduce the available water. Because they are separate requirements that are trying to accomplish different goals, the fire flow, per NFPA 1, is not required to be added to the demand of an automatic sprinkler system in sprinklered buildings. However, the available water supply must be the greater of the two, either the sprinkler system demand, or the required fire flow. If the available water supply can support the greatest demand, it will also be able to support the other demand as well. NFPA 1, provides requirements for fire flow in Section 18.4. The requirements are performance-based, which means they do not specify the type of system necessary to provide the required fire flow. The AHJ (typically the responding fire department) has the final authority to determine if the proposed water supply delivery method is appropriate. Fire flow is calculated based on the fire flow area of the building. The flow area is the total floor area of all floor levels of a building, except for Type I (443), Type I (332), and Type II (222), in which case the fire flow area is the largest three successive floors. The fire flow area should be determined based on the area between the surrounding exterior walls of each floor and the fire separation walls used to create separate buildings.   Table 18.4.5.2.1 lists the minimum required fire flow and flow duration for buildings based on fire flow area and construction type. For more information on construction types, take a look at this blog.  For example, a Type I (443) building with a fire area in the range of 0-22,700 ft2 (0-2108.83 m2) is required to provide the fire department with a fire flow of 1500 gpm (5677.5 L/min) for a flow duration of 2 hours (see below). Enlarge image Paragraph 18.4.5.3.2 states that the required fire flow for buildings other than one and two family dwellings can be reduced by 75 percent when the building is protected by an approved automatic sprinkler system. However, the resulting fire flow cannot be less than 1000 gpm (3785 L/min) or 600 gpm (2270 L/min) where quick response sprinklers are used throughout. Sprinklered one- and two -family dwellings fire flows can be reduced by 75 percent with no minimum and the duration decreased to one hour. Here is an example video stepping through the calculation of the required fire flow taken from our Certified Fire Plans Examiner Learning Path. As mentioned, hydrants are the primary method for providing a fire flow. NFPA 1 requires that the flow capacity of all fire hydrants within 1000 ft (305 m) of a building not be less than the required fire flow. The distance should be measured as the fire apparatus would lay hose out on the fire department access road to the building. The distance should not be measured across adjacent lots or through fences, gates, or other obstructions that would prevent the normal movement of a fire apparatus performing a hose lay to a fire hydrant. Table 18.5.4.3 of NFPA 1 specifies the maximum capacity that each hydrant can be credited for when calculating the total available fire flow, based on the distance of the hydrant from the building. Enlarge Image Fire Hydrants must be installed to meet the requirements of NFPA 1, waterworks standards, and any local requirements of the jurisdiction. Where required by the Authority Having Jurisdiction (AHJ), the hydrant needs to be provided with a reflector and proximity flag. In some jurisdictions, the hydrants are also color-coded to indicate the available flow rate. Fire hydrants need to be located within 600 feet (183 m) from the closest point of the building in detached one- and two-family dwellings, with a maximum spacing of 800 feet (244 m). For buildings other than one- and two-family dwelling, hydrants need to be within 400 feet (122 m) of the building with a maximum spacing of 500 feet (152 m). Additionally, hydrants must also be located within 12 feet (3.7 m) of the fire department access road. If you are interested in learning more about fire plans review, or want to become a Certified Fire Plans Examiner, take a look at our learning path explorer module, which provides some sample lessons. 
Person testing alarm

Smoke Alarm (Smoke Detector) Troubleshooting

A working smoke alarm in your home can alert you to a fire, giving you time to safely get out of the house. Knowing the different sounds, a smoke alarm makes is key to understanding what to do.  If your smoke alarms sound, you should exit the house as soon as possible and follow your home fire escape plan. However, if you keep having nuisance (unwanted) smoke alarms when there is no fire, here are a few things that can help you determine the issue.   I also want to note that there is a difference between a smoke detector and a smoke alarm, basically a smoke detector is just a sensor that monitors for smoke and is connected to a whole building fire alarm system, while a smoke alarm has both the sensor to monitor for smoke and a speaker that emits the sound to notify the occupants in the home.  For this discussion I am referencing home smoke alarms. Here is a quick guide to use if you are trying to figure out the sounds coming from your smoke or carbon monoxide alarms. I will explain all of these in more detail below.   One alarm can cause all of them to go off Some smoke alarms can be interconnected so that when one detects smoke, all of them go off. This is important because a fire in another portion of your home can be causing all your smoke alarms to be going off to alert everyone in the home. A single faulty smoke alarm can also cause all your smoke alarms to go off when there is no fire. If all the alarms are going off without a fire, you need to identify which smoke alarm is the one that is initiating the alarm.  You can determine this by checking the instructions printed on the back of one of the alarms to see how the specific model of smoke alarm identifies the initiating alarm. Typically, this is indicated with a led light indicator on the initiating smoke alarm. You may also be able to hit the silence button on any smoke alarm, which will cause all the non-initiating smoke alarms to silence so you can hear just the initiating one.  Once you have determined which one is initiating the alarm and there is not a fire, there may be a few reasons for this alarm sounding. It could be a carbon monoxide (CO) alarm You can’t see or smell carbon monoxide (CO), but it is still very deadly. In your home carbon monoxide may be released by a malfunctioning gas or oil-fed appliances (stove, water heater, furnace), a fireplace, or even a car running in the garage. Whether you have a combination smoke/CO alarm or separate CO alarm, if the sound you are hearing is a temporal 4 pattern (see video below), meaning there are 4 beeps followed by a pause repeatedly, the alarm you are hearing is for carbon monoxide. Exit your home immediately and call 911 so the fire department can come investigate the issue. A combination smoke alarm/ CO alarm will look the same as a smoke alarm (see image below).   The alarm could be dirty If you have determined that the alarm is a smoke alarm, meaning it is a temporal 3 (three beeps and a pause) (see video below) and not a CO temporal 4 (4 beeps and a pause), then it is possible that the smoke alarm is dirty.  Dust, dirt, and even spiders can get into an alarm and make it falsely sound. They can be cleaned with a vacuum or compressed air. Look at the back of the alarm to see if the manufacturer specifies one cleaning method over the other and to see the recommended frequency. The image below shows that this manufacturer recommends vacuuming the alarm monthly.     Steam can be the problem If your smoke alarm is mounted near a bathroom, it is possible that steam from the shower has set off the alarm. Alarms should be placed at least 36 in. (910 mm) from the bathroom door to eliminate the nuisance alarms from steam. Areas of high humidity or spaces with a humidifier can also cause issues with the alarm. If the smoke alarm is installed near a cooking appliance (stove, oven, etc.) it could falsely alarm, so consider moving the alarm further from the appliance. How is the temperature? Smoke alarms are designed to be used in a specific temperature range, typically 40F to 120F (4C to 49C). If the temperature has risen above or fallen below those temperatures (such as freezing in a garage) it is possible for there to be a false alarm. Check the manufacturer’s instructions for the required temperature range. If your alarm is chirping If the sound you hear is a “chirping” sound or a very short beep (see video below) then the alarm is notifying you that there is an issue with the alarm. Look at the back of the alarm for the description of the different types of sounds and what they mean as each alarm is different (example shown below), but in general a single repeated chirp can mean one of the following: The battery is dying. If the alarm has replaceable batteries, replace them. If it is a sealed unit with a 10-year battery, replace the alarm. End of Life means that if the alarm is nearing or past 10 years from the date of manufacturer, it will need to be replaced.If the alarm is less than 10 years old and new batteries still result in chirping, replace the alarm anyway.     Continued Issues If you are still having issues with your smoke alarm that you cannot figure out, look on the back of the alarm for information on how to contact the manufacturer for troubleshooting. Additionally, if you would like someone to come out and inspect the alarm(s), most municipal fire departments or local fire marshals are willing to come out and look. Just give the fire department a call on their non-emergency line or call the fire prevention department. Learn more To learn more about the different types of smoke alarms and how to choose the best alarm, read my blog on purchasing smoke alarms, or check out our Fire Prevention Week Website, Public Education Smoke Alarm Page, Carbon Monoxide Alarm Page, or Chapter 29 of NFPA 72®, National Fire Alarm and Signaling Code®. Important Notice: Any personal opinion expressed in this blog is the 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.
Person testing alarm

What kind of smoke alarm (smoke detector) should I buy?

Smoke alarms are important to fire safety in your home because, the risk of dying in home structure fires is 55 percent lower in homes with working smoke alarms than in homes with no alarms or none that worked. Buying smoke alarms can be a bit confusing to someone who is not aware of all the different types and the terminology being used. Because of this, I am going to break down some of the most frequently asked questions to help you choose the best alarm. I want to note that there is a difference between a smoke “detector” and a smoke “alarm”, basically a smoke detector is just a sensor that monitors for smoke and is connected to a whole building fire alarm system, while a smoke alarm has both the sensor to monitor for smoke and the speaker that emits the sound to notify the home occupants. What are the different types of smoke alarms? Having the proper number of working smoke alarms installed (regardless of the type) in the correct locations is key when it comes to safety. Ionization vs Photoelectric There are some different types of alarms that can be purchased that have different pros and cons. The first difference you will see is Photoelectric vs Ionization. The difference between the two types is the sensor that is used to detect the smoke. An ionization smoke alarm is generally more responsive to flaming fires (imagine a fire where you can see the flame), and a photoelectric smoke alarm is generally more responsive to smoking smoldering fires (such as a cigarette). Ionization Ionization smoke alarms utilize a small amount of radioactive material to ionize air molecules into positively and negatively charged molecules that create a small electric current. The introduction of smoke into that ionized air will reduce the amount of current and cause the smoke alarm to sound. Typically, smoke alarms with Ionization detectors tend to be less expensive than alarms with photoelectric detectors.                    Photoelectric Photoelectric smoke alarms utilize a light source and a photosensitive cell. When smoke enters the chamber, light scatters and is picked up by the photosensitive cell, causing the alarm to sound.            Combination Ionization and Photoelectric To get an alarm that is just as responsive to smoldering fires as it is to flaming fires, you can get an alarm that has dual sensors. These alarms have both an ionization sensor and a photoelectric sensor that will cause the alarm to sound. A dual sensor alarm provides the best protection and for that reason it is recommended.   Intelligent multicriteria alarms There are alarms available that are multicriteria or intelligent alarms, what this means is they use many different sensors such as photoelectric, ionization, and heat along with an algorithm to detect a fire. Because of the multiple sensors, this type of alarm is better at reducing unwanted, or "nuisance” alarms from non-fire sources (such as when you are cooking), it does not necessarily mean that the alarm is able to detect fires sooner. Voice smoke alarms There are some smoke alarms available that will produce both the temporal 3 pattern (a continued set of three loud beeps -- beep, beep, beep) as well as having a voice announcement that can tell you things like where the smoke is being detected or if there is an issue with the smoke alarm. What is a combination smoke and Carbon Monoxide (CO) alarm? A combination smoke carbon monoxide alarm is an alarm that has both sensors to sense smoke and to sense for carbon monoxide. These alarms may look like smoke alarms and are mounted on the ceiling or the wall near the ceiling. If your house has fuel burning equipment (oil or gas boiler, oil or gas furnace, oil or gas water heater, fire-place ect.) then you will need to also have carbon monoxide detection within your house. How do smoke alarms get their power? There are many ways that smoke alarms can get their power. Replaceable batteries Some smoke alarms will get all their power from batteries that are replaceable, they can be a 9v battery, AAA battery, AA battery, or another type of battery. These batteries should be replaced at least once a year and the alarm tested every month. 10-year battery alarms Some smoke alarms come with a sealed non-replaceable battery that can provide power to the smoke alarm for up to 10 years. This alarm does not require the batteries to be replaced, however, you should still be testing them monthly. Hardwired with battery backup Some smoke alarms are provided with both primary power that is hardwired in from the home’s electrical system and a secondary battery backup. The secondary battery backup can be either a battery that needs to be replaced at least yearly, or it can be a 10-year sealed battery that does not need to be replaced. Do I need battery or hard-wired smoke alarms? If your home has hard wired connections, then you should replace the alarms with hard wired smoke alarms of the same manufacturer. You can use a different manufacturer; however, this may require an electrician to come in and wire in a different plug (also see the interconnection section below). If you are performing renovations or building a new home, check with the local building department and/or fire department for code requirements. How often do I need to replace my smoke alarms? Smoke alarms must be replaced: Every 10 years based on date of manufacturer on the back label (7 years for Combination CO/Smoke Alarm) if the alarm sounds an end-of-life signal (see back of alarm for description of signal) if the alarm fails a monthly operability test or, after a fire event How do I know I am buying a quality alarm I can rely on? Smoke alarms are required to be tested by a third party recognized laboratory to stringent product standards. Make sure that the alarm you are buying was tested by and labeled (shown on packaging and on the label of the alarm) by a recognized testing laboratory. Some examples include Underwriters Laboratories (UL) and Intertek.      What are interconnected smoke alarms, and do I need them? Smoke alarm interconnection means that the alarms are connected so that if one alarm sounds, all the alarms in the home  will sound. Interconnected smoke alarms are more likely to alert occupants of a fire anywhere in the building. Because of this, new building, fire, and life safety codes will require smoke alarms in new buildings or remodeled buildings to be interconnected. Typically, if you are just replacing an alarm, then you can replace them with the same type that was there, if they are currently interconnected then you need to replace with interconnected, if they are not interconnected, you are not required to install interconnected alarms, however, interconnected alarms will provide an additional level of safety. It is especially important to have interconnected smoke alarms, if you sleep with doors closed.    You can get smoke alarms that are interconnected with a wire or that are wireless. If your smoke alarms are hard-wired look to see if there are three wires coming from the alarm, if they are all connected, then it is likely the alarms are interconnected. If the smoke alarms are not hard-wired, then you will need to look on the alarm to see if it is capable of being wirelessly interconnected. You can also just press the test button on one alarm and listen to see if the other alarms in the house go off, if they do then you have interconnected smoke alarms.    When interconnected smoke alarms are installed, it is important that all the alarms are from the same manufacturer or are listed as compatible (see manufactures instructions for compatible alarms). If the alarms are not compatible, they may not sound. In what rooms do I install smoke alarms? Check your local building, fire, or life safety codes for your specific requirements, you can call your local fire prevention department as well. But in general smoke alarms need to be installed: Inside each bedroom, outside each sleeping area (such as in the hallway) and on every level of the home, including the basement. On levels without bedrooms, install alarms in the living room (or den or family room) or near the stairway to the upper level, or in both locations. Smoke alarms installed in the basement should be installed on the ceiling at the bottom of the stairs leading to the next level. Larger homes may require additional smoke alarms Do I install the alarm on the ceiling or the wall?  Mount smoke alarms high on walls or ceilings (remember, smoke rises). Wall-mounted alarms should be installed not more than 12 inches (300 mm) away from the ceiling (to the top of the alarm).  If you have ceilings that are pitched, install the alarm within 36 inches (910 mm) of the peak but not within the apex of the peak (4 inches (100 mm) down from the peak). Avoid installing the smoke alarms in places where there is air movement or drafts such as near windows or near the air supply from an HVAC system.        How do I reduce unwanted alarms? If you are required to place a smoke alarm near cooking appliances or the door to a bathroom based on the arrangement of your house, there are some things to keep in mind to reduce any unwanted alarms.      To limit the amount of unwanted alarms from cooking, you should place your alarm at least 20 feet (6.1 m) from the cooking appliance. If the alarm is a photo-electric type, has a silencing button, or is listed for a resistance to common cooking smoke then you can place it as close as 10 feet (3.0m) away from the cooking appliance. If placing a smoke alarm in the hallway near the door to the bathroom with a shower in it, you should place it at least 36 inches (910 mm) from the door to reduce the impact of steam from the shower on the alarm. What if someone in my home is deaf or hard of hearing? There are smoke alarms and alert devices that alert people who are deaf or hard of hearing. These devices include strobe lights that flash to alert people when the smoke alarm sounds. Pillow or bed shakers designed to work with your smoke alarm also can be purchased and installed. Learn more If you would like to learn more about smoke alarms or carbon monoxide alarms, check out our public education smoke alarm page, Carbon Monoxide alarm page, or Chapter 29 of NFPA 72®, National Fire Alarm and Signaling Code®.  

Standpipe System Design and Calculations

Standpipe systems consist of piping and hose connections installed throughout a building to provide reliable water for the manual suppression of a fire by either the fire department or trained personnel. NFPA 14, Standard for the Installation of Standpipe and Hose Systems, Chapter 6, outlines design and installation requirements for standpipe and hose systems. Standpipe systems can be broken down into different types of systems to delineate whether the piping is full of water (wet) or not (dry) and whether the water supplied for firefighting is automatically provided by a water supply, such as a city main or a tank and fire pump (automatic or semi-automatic), or needs to be provided by a fire department pumper (manual). When designing a system, you first need to determine the supply pipe size, hose connection location, size, and pressure based on the standpipe classification. There are three classes of standpipe systems, they include Class I, Class II, and Class II. Class I Class I systems are installed for use by the fire department and are typically required in buildings that have more than three stories above or below grade because of the time and difficulty involved in laying hose from fire apparatus directly to remote floors. Class I systems are also sometimes required in malls, because these occupancies contain areas that are difficult to access directly with hose from fire apparatus. Locations for hose connections in Class I systems include: Each main floor landing or intermediate landing of required stairs. On the roof if the stairwell does not have access to the roof. Each side of exit openings in horizontal exits. Exit passageways. Additional hose connections should be available in unsprinklered buildings where the distance from a hose connection to the most remote part of the floor exceeds the limits in NFPA 14 based on the sprinkler system type and building type. The minimum residual pressure required for a Class I system is 100 psi (6.9 bar) from the hydraulically most  remote 2 ½ in. (65 mm) hose connection with a flow rate of 500 gpm (1893 L/min), through the two most remote 2 ½  in. (65 mm) hose connections. A pressure-regulating device may need to be used in order to limit the pressure at hose connections to less 175 psi (12.1 bar) static (pressure when not flowing).            Class II Class II are installed for use by trained personnel and are often required in large un-sprinklered buildings. They might also be required to protect special hazard areas, such as exhibit halls and stages. In the past, Class II standpipes were typically installed with a hose, nozzle, and hose rack on each hose connection. Prior to the 2007 edition of NFPA 14, Class II systems were defined as being for use “primarily by the building occupants or by the fire department.” Because of concerns regarding the ability of untrained occupants to safely use the hose and the encouragement of occupants to fight the fire rather than evacuate, the Technical Committee chose to define Class II systems as being for use by “trained personnel or by the fire department.” Class II systems need to provide enough hose stations so that all portions of each floor level of the building are within 130 ft (39.7 m) of a 1 ½ in. (40 mm) hose connection provided with 1 1∕ 2 in. (40 mm) hose or within 120 ft (36.6 m) of a hose connection provided with less than 1 1½ ∕ 2 in. (40 mm) hose connection. The minimum residual pressure required for a Class II system is 65 psi (4.5 bar) from a remote 1 -1/2½ in. (40 mm) hose connection with a minimum flow rate of 100 gpm (379 L/min). A pressure-regulating device may need to be used in order to limit the pressure at these hose connections to less than 100 psi (6.9 bar) residual (pressure when flowing) and 175 psi (12.1 bar) static (pressure when not flowing). Class III Class III systems combine the features of Class I and Class II systems. They are provided for both full-scale and first-aid firefighting. These systems are generally intended for use by fire departments and fire brigades. Because of their multiple uses, Class III systems are provided with both Class I and Class II hose connections and must meet the placement, pressure, and flow requirements for both Class I and Class II systems. Pipe sizing The minimum size pipe for Class I and III standpipes is 4 in. (100 mm). If the standpipe is part of a combined sprinkler system in a partially sprinklered building, that is increased to 6 inches (150 mm). If the building is protected with an automatic sprinkler system, then the minimum combined standpipe size can be 4 in. (100 mm) if hydraulically calculated. The branch lines of the standpipe system are to be sized hydraulically but cannot be smaller than 2 -1/2½ in. (65 mm). Calculating Hydraulically calculating a standpipe system is very similar to that of a sprinkler system because we are calculating the pressure lost in the system to get the required flow to the most remote hose connection. In addition to the required flow from the most remote hose connections, based on the classification we are required to also calculate flow from connections on each standpipe. For example, when calculating a Class 1 Standpipe system in a building that is less than 80,000 ft2 (7432m2) we need to calculate the flow rate of 500 gpm (1893 L/min), through the two most remote 2 ½  in. (65 mm) hose connections at 100 psi (6.9 bar) and also calculate an additional 250 gpm (946 lpm) flowing from each standpipe in the building up to a maximum total flowrate of 1000 gpm (3785 L/⁠min) for buildings that sprinklered throughout, and 1250 gpm (4731 L/min) for buildings that are not sprinklered throughout. Take a look at this video taken from our soon to be released Online Certified Water-Based System Professional Learning Path discussing how to hydraulically calculate a standpipe system. Want to Learn More? Keep an eye out for our Certified Water-Based Systems Professional Learning Path. Also, If you found this article helpful, subscribe to the NFPA Network Newsletter for monthly, personalized content related to the world of fire, electrical, and building & life safety.
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