High-bay presents unique challenges
This month's panel discusses fire detection and suppression challenges in high-bay environments—what systems are ideal what technological advances have been made. CSE: What are the unique design challenges in fire detection and suppression systems for high-bay environments? GOLDHAMMER: Design challenges depend on the type of fire scenario anticipated for the expected occupancy.
This month's panel discusses fire detection and suppression challenges in high-bay environments—what systems are ideal what technological advances have been made.
CSE: What are the unique design challenges in fire detection and suppression systems for high-bay environments?
GOLDHAMMER : Design challenges depend on the type of fire scenario anticipated for the expected occupancy. For high-bay areas, where the heat release rate is high, the size of the fire and size of the fire plume will increase—suppression systems must be designed accordingly. For low heat release rate fires, there may be stratification of the fire/smoke plume, resulting in ceiling level detection and suppression systems malfunctioning. Designers must take into consideration many variables including fuel load, ceiling height, occupancy, and construction when designing these systems.
ALLEN : There are many types of high-bay environments, but two are most commonly encountered: warehouses, where large quantities of combustible materials are stored 50 ft or higher; and in atriums and facilities such as indoor stadiums.
In the case of warehouses, research and fire testing has led to the development of new types of sprinklers. These sprinklers are designed to discharge larger amounts of water with larger droplet sizes than traditional standard spray sprinklers. NFPA Standard 13 “Installation of Sprinkler Systems” provides a number of design requirements. To properly apply these requirements, the designer must have detailed knowledge of the materials to be stored and the storage arrangement, including types of racks, aisle widths, maximum storage height and clearance to the ceiling and roof.
For atriums and similar environments, the amount of combustible materials and heat release rates would be much less than in the case of warehouses. As the ceiling height increases above 50 ft, automatic sprinkler protection becomes less effective due to the possibility of delayed activation, water droplets that are unable to penetrate the fire plume, and the possibility of sprinkler activation in areas not directly above the fire due to air movement.
CSE: What types of heat and smoke detection systems are ideal for high-bay applications?
ALLEN : In atriums and similar environments, ceiling-mounted smoke detectors may not activate, especially in the early stages of a fire, due to smoke stratification. A hot-air layer frequently forms under the ceiling of an atrium. This hot-air layer may be hotter than the smoke rising from the fire below, which prevents the smoke from reaching the detectors. Beam smoke detectors often are used to detect the developing smoke layer. To determine the most advantageous location and spacing of beam detectors, the designer calculates the expected plume diameter and locates the detectors to accommodate the plume dynamics.
GOLDHAMMER : For high heat release rates, standard smoke detection can be effective. For lower heat release rates, where stratification is a concern, use of beam detection, air sampling technology, and even video detection may be appropriate. Ultraviolet infrared detection also may be appropriate for deluge-type sprinkler system applications.
CSE: There are many technological advances in fire protection for high-bay racking systems. What types of systems are the most popular nowadays: in-rack, early-suppression fast-response (ESFR), large orifice sprinklers?
GOLDHAMMER : My experience with clients is to avoid rack sprinkler protection when possible. In many applications, the use of ESFR technology does not require rack sprinklers. This especially is true with the larger orifice/k-factor heads. Full-scale fire testing has demonstrated superior suppression capability of ESFR technology. However, ESFR technology is limited to certain storage and ceiling heights. Using ESFR outside of the testing criteria may lead to rack sprinklers or even barrier sprinkler protection schemes.
ALLEN : For warehouses, ESFR sprinklers provide the best solution, because numerous storage arrangements and commodity types are protected without using in-rack sprinklers. Eliminating the need for in-rack sprinklers provides more flexibility in changing rack arrangements and the potential for damage to in-rack sprinkler piping. Because ESFR sprinklers can be used for many different types of storages, they provide a sprinkler design that is used in warehouses where tenants or storage arrangements change.
CSE: Beyond the types of suppression systems mentioned above, what other new technological innovations have there been for these sprinkler systems?
GOLDHAMMER : Some of the latest technological innovations are based on the use of full-scale fire testing. Examples include using different k-factors (orifice sizes) and operating end head pressures to achieve adequate protection solutions to the high bay environment. Fire testing also has shown that adequate protection can be achieved using the declining density method, which uses higher end head pressures during initial sprinkler head operation.
ALLEN : In aircraft hangars, foam-water sprinkler systems and low-level underwing AFFF systems are used.
CSE: What are some of the most common design errors in systems for high-bay?
ALLEN : The installation rules in NFPA 13 are specific for ESFR sprinklers, including the maximum pitch of ceilings and clearance from obstructions. Without attention to detail in the design and installation, ESFR sprinklers may not be installed in accordance with the requirements. The suppression principle of ESFR sprinklers is for sprinklers to operate in the early stages of a fire by using a more sensitive thermal element (response time index) than standard sprinklers and to discharge a large amount of water from each operating sprinkler. As a result, a limited number of sprinklers—typically 12—are included in the hydraulic design criteria. If the water discharge from ESFR sprinklers is obstructed, they cannot deliver the necessary amount of water to the fire. The continued growth of the fire beyond that which is contemplated in the sprinkler design may result in additional sprinklers operating. The additional sprinklers may not be supported by the water supply and sprinkler piping design.
Due to obstructions requirements for ESFR sprinklers, the building design, including size of bays, spacing of roof structural members, and roof slope, should be coordinated with the sprinkler design in the early stages of the project.
GOLDHAMMER : Often we encounter buildings that are shell designs with an unknown future tenant. Fire protection in these buildings is often based on minimal protection to reduce cost for the owner—later resulting in costly upgrades that are not anticipated by the tenants.
ESFR systems should be coordinated up front with the various trades, including architectural, structural, mechanical, and electrical. ESFR systems are prone to obstructions due to the technology. Coordination and field observation is critical to avoid last minute issues.
CSE: Do you see clean agent suppression systems being increasingly specified for high-bay environments? When do you specify special suppression instead of sprinklers?
GOLDHAMMER : Sprinkler systems are the best available protection. However, clean agent suppression systems may be applicable in sensitive environments such as research, testing and fabrication.
ALLEN : Of course, local application CO2 systems have been used for years in industrial settings, such as for turbine-generators in power plants, rolling mills in steel plants, and other high bay areas. The new clean agents (halocarbon agents and inert gas agents, as covered by NFPA 2001) are currently recognized for total flooding applications only. Their use in typical high bay areas such as atriums is inappropriate due to the large volumes and need for boundaries that can contain the required agent concentrations.
CSE: What are some of the jurisdictional and regional differences that you know of with respect to specifying fire protection equipment for high-bay areas?
GOLDHAMMER : Some of the major differences we encounter are the way jurisdictions handle spec warehouses. It ranges from minimal protection requirements to protection for a worst case commodity and storage arrangement. In occupancies with low heat release rates, we have been required to provide monitor nozzles at the ceiling level to account for no sprinkler head activation.
CSE: To what degree are building automation systems an integral part of fire protection for high-bay environments?
GOLDHAMMER : Building automation systems typically are not part of the fire protection systems. However, for certain applications, automatic retrieval systems may be interlocked to shutdown upon activation of a water flow alarm.Air handling systems may be interlocked to provide smoke removal capabilities upon activation of a water flow alarm.
ALLEN : Smoke control systems often are integrated with the building automation system rather than designed as standalone systems. Where this is the case, it is important that the smoke control components meet the code requirements. For example, the IBC (International Building Code) Section 909.12 requires that control units providing input or output signals to mechanical smoke control systems comply with UL 864. Section 909.13 provides requirements for control air tubing. The designer must properly specify the equipment because normal BAS systems may not meet these requirements.
In warehouses where ESFR sprinklers are used, natural and powered roof ventilation may delay sprinkler operation if the vent captures the fire plume or if air velocity at a sprinkler is too high. Although not referenced by NFPA 13, FM Global Data Sheet 2-2, Installation Rules for Suppression Mode Automatic Sprinklers, indicates that the air velocity at sprinklers should not exceed 5 fps. As previously discussed, the design and installation of ESFR sprinklers requires consideration of many building features, including normal ventilation and smoke-and-heat venting, that are not a factor with standard sprinklers.
CSE: Are there any recent code changes that you know of regarding fire protection for high-bay areas?
GOLDHAMMER : NFPA 13 2007 edition has added further clarification regarding ceiling heights and clearances. In addition, design criteria using various k-factors, operating pressures, and storage and ceiling heights have been added based on the use of full-scale fire testing.
ALLEN : NFPA 13 continues to reflect new design information for sprinkler protection of storages based on testing and listing of newly development sprinklers.
For smoke control systems in atriums, the IBC requirements have changed in the 2000, 2003 and 2006 editions. The 2006 edition eliminated the prescriptive requirements of previous editions, referencing NFPA 92B, which allows an overall review of smoke layer movement. Computer modeling provides a more realistic understanding of smoke movement, especially in spaces with unusual configurations. Coupled with egress modeling, a performance design can demonstrate safety to occupants for the time needed for egress with cost-effective smoke control designs.
Thomas L. Allen , PE
Senior Consulting Engineer, Rolf Jensen & Assocs. Inc., Laurel, Md.
Edward S. Goldhammer , PE
Regional Engineering Manager, Schirmer Engineering Corp., Las Vegas