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.

NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, provides the criteria for the routine activities that must be conducted to ensure that water-based fire protection systems can be relied upon in the event of a fire. These activities range from simple visual confirmation of some things such as valve position and room temperature on a more frequent basis, to much more complex activities such as full flow tests and internal assessments at longer intervals.  All of these activities are intended to keep sprinkler systems in working order. But what about when a system needs to be shutoff for repair or maintenance? What about when a water main is broken, a frozen pipe has burst, a fire pump has failed, or another major issue has been found during inspection or testing? At that point, the building contains a compromised sprinkler system and is no longer protected at the level that is expected while the system is in service. In NFPA 25, the term for a system that is out of order, is impairment, regardless of whether or not it was planned (see Deficiencies and Impairments of Sprinkler Systems). Impairments need to be addressed and resolved as quickly as possible in order to provide the expected level of protection for life and property. If the impairment is prolonged, additional measures need to be taken in consideration of life and property protection. Planning ahead Chapter 15 of NFPA 25 is dedicated to addressing the requirements that include the measures to be taken to ensure that increased risks are minimized, and the duration of the impairment is limited. A key provision here is that the property owner or designated representative must assign an impairment coordinator to comply with the requirements of the chapter (see Responsibilities of the Building Owner for Fire Sprinkler System Inspection Testing and Maintenance). The impairment coordinator should have a detailed plan, ahead of time for how they will handle both preplanned and emergency impairments and meet the requirements detailed below. Any preplanned impairments need to be authorized by this individual prior to removing the system from service. Tag Impairment System A tag must be used to indicate that a system, or part of the system, has been removed from service. The tag must be posted at each fire department connection and the system control valve, and other locations required by the authority having jurisdiction, indicating which system, or part, has been removed from service. Anyone who is shutting down a system should use tagging procedures even if the owner does not. Tags can also be itemized in a list to facilitate proper restoration of the system to working order. As tags are retrieved, they can also be used for verification that a valve or system has been restored to service. Impairment program While the system is out of service, NFPA 25 provides details on impairment programs and what they should cover: Determination of the extent and expected duration of the impairment Inspection of the area or buildings involved and determination of increased risks Submission of recommendations to mitigate any increased risks Notification of the fire department Notification of the insurance carrier, alarm company, property owner, and other authorities having jurisdiction Notification of supervisors in the areas affected Implementation of a tag impairment system Prolonged impairments In addition to these steps, what may be the most important or impactful provision is arranging for one or more of the following measures when the fire protection system is out of service for more than 10 hours in a 24-hour period: Evacuation of the building or portion of the building affected by the system out of service Implementation of an approved fire watch program Establishment of a temporary water supply Establishment and implementation of an approved program to eliminate potential ignition sources and limit the amount of fuel available to a fire Restoring systems to service When repair work has been completed and the system is restored to service, the following items need to be confirmed: Any necessary inspections and tests have been conducted Supervisors have been advised that protection is restored The fire department has been advised that protection is restored The insurance carrier, alarm company, property owner, and other authorities having jurisdiction are notified that protection is restored The impairment tag(s) are removed While we certainly hope that fire sprinkler systems can be maintained in continuous service there are times where planned service, maintenance activities or unexpected circumstances cause the system to be out of service. Assigning an impairment coordinator, planning ahead, and understanding Chapter 15 of NFPA 25 will help to minimize the risk posed while the system is impaired.

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.

At the first NFPA meeting in 1896 the first consolidated set of sprinkler installation rules were established, becoming what is today known as NFPA 13, Standard for the Installation of Sprinkler Systems. Formalizing the sprinkler installation standards increased fire sprinkler effectiveness, however, a gap still existed in the use of fire sprinkler systems. In 1933 a brochure titled “Use of Automatic Sprinklers by Fire Departments” was published providing fire departments with guidelines on how to best capitalize on the effectiveness of fire sprinkler systems during incidents. This brochure evolved over the next 33 years into the Recommended Practice for Fire Department Operations in Properties Protected by Sprinkler and Standpipe Systems, NFPA 13E first published in 1966. Today NFPA 13E provides the information necessary to ensure fire departments are trained on and operate effectively with automatic fire sprinkler systems. Although some fire sprinkler systems are designed to suppress a fire, most are designed to control a fire. The main difference between fire control and fire suppression is related to the fire sprinkler systems impact on the fires heat release rate. The graph below depicts fire control (dotted line) versus fire suppression (solid line). Fire sprinklers controlling a fire result in a steady heat release rate, keeping the fire from growing, and fire sprinklers suppressing a fire will result in a decreasing heat release rate. The three principal causes of fire sprinkler system failures identified in NFPA 13E are a closed control valve, inadequate water supply for the system and occupancy changes that render the installed system unsuitable. Beyond the primary causes found in the recommended practice, NFPA has conducted research on the U.S. Experience with Fire Sprinklers to help understand fire sprinkler effectiveness. Let’s take a second to review the three main causes found in the recommended practice all of which responding fire department personnel can impact positively. Closed control valve Familiarization with the types of control valves and their layout in a system allows firefighters to both understand what valves will disrupt water flow and what position have they should be in for effective operation. Should they encounter a valve which is not in the correct position during a fire, placing that valve in the correct position may restore the system effectiveness. This is not a hard and fast rule however, since the fire may have already operated more sprinkler heads than the available water supply can support, making the system ineffective. Additionally, fire departments should never turn off a sprinkler system that has activated until they have confirmed the fire is fully extinguished and overhaul has taken place. Even if ventilation is needed to increase visibility and conduct search and rescue, the system should remain operational to control the fire as these tasks occur. Once this occurs, steps should be taken to identify if only a portion of the system needs to be shut down (a zone) rather than the entire system. Anytime the system is shut down a firefighter with a portable radio should remain at the control valve to immediately open the valve should the fire not be fully extinguished. Simply turning the system back on may not reestablish fire control. Fire sprinkler systems are designed to control a fire utilizing a specific number of sprinklers at a design pressure and flow. If the system is shut off prior to the fire being extinguished the potential exists for additional heads beyond the design to activate. When the system is turned back on the available water supply may not cover the operated heads leading to ineffective water application and a fire that is no longer controlled. Inadequate Water Supply The water supply may be inadequate due to a lack of available water flow, lack of available pressure or both. Since fire department pumpers often have the capacity to supply water at higher flow rates and pressures than the normal water supply, utilizing a fire department pumper to supply water to the fire department connection (FDC) can address most inadequate supply concerns. The FDC will often bypass many of the control and check valves in the system, supplying water directly to the operating sprinklers. NFPA 13E recommends a pressure of 150 psi (10 bar) to effectively suppl fire sprinkler systems, unless additional signage is provided to indicate a different pressure. The fire department can also have a negative impact on the water supply to a fire sprinkler system. Although fire sprinkler systems are designed with a hose stream allowance or amount of water the fire department may potentially need to fully extinguish the fire, this may not be sufficient. For more information on fire flow check out this blog Calculating the Required Fire Flow. The hose allowance accounts for water needed at the base of the fire, which if the fire department cannot effectively apply water to the base of the fire, more may be needed. Utilizing more water from the supply than accounted for has the potential to reduce the sprinkler system effectiveness, eliminating its ability to control the fire, resulting in fire growth and the need for more water. Supporting the system through the FDC ensures that even if more water is needed than the original allowance, the sprinkler system still has an available supply at an effective flow and pressure. Occupancy changes Although the fire department does not have an ability to impact occupancy changes during a fire incident, an effective preplan and inspection program has the potential to identify occupancy changes which can adversely impact fire sprinkler system effectiveness before fires occur. Training those conducting these inspections to understand what types of commodities would represent a high heat release rate fire and how to identify if a sprinkler system could be designed to deliver the necessary water density can reduce this potential cause of failure. Summary As with all NFPA recommended practices, the language is less rigid than a standard or code, utilizing “should” instead of “shall” as to not limit the individual fire departments, allowing them to adopt more effective procedures. Familiarization with NFPA 13E provides anyone who may be utilizing a fire sprinkler system the knowledge necessary to positively impact the systems effectiveness.  Check out NFPA 13E to help your department identify the recommended training and operations for those responding to emergencies involving activated fire sprinkler systems. Interested in learning more, check out the resources below for additional information on fire sprinkler systems and fire department access. Sprinkler system Basics: Types of Sprinkler Systems The Basics of Sprinkler Thermal Characteristics Types of Sprinklers NFPA 1: When is Fire Department Access Required?

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.

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.