Recently completed FM Global research has led to a new understanding of how in-rack sprinklers can be deployed in high-rack storage facilities to maximize protection and reduce cost.
The research is part of FM Global's overall business strategy to advance fire protection and help clients minimize property loss. The new guidelines offer FM Global clients better, simpler, more cost-effective and flexible in-rack sprinkler options.
The new protection guidelines greatly reduce the number of in-rack sprinklers needed, maximize their vertical spacing and reduce installation costs by more than 40 percent when compared to today's inrack sprinkler design guidelines. The guidelines were unveiled publicly in FM Global Property Loss Prevention Data Sheet 8-9, Storage of Class 1, 2, 3, 4 and Plastic Commodities.
"We're kind of blowing the top off of everything we've done in the past," says FM Global's Senior Research Engineer Kristin Jamison.
The new guidelines are based on a three-year research project utilizing small-, intermediate- and large-scale testing as well as fire modeling technology that is continuously being developed by FM Global. The new design is based on a primary understanding of how fire develops within a storage rack as well as how the water flow from in-rack sprinklers interacts with a fire.
It also takes a revolutionary approach by using quick-response, high K-factor sprinklers. (The higher the K-factor the more water can flow through the sprinkler.) These high K-factor sprinklers have been designed for and deployed in ceiling-level sprinkler projection but are not generally used, or tested, for in-rack sprinklers.
Historically, in-rack sprinkler systems were designed using K5.6 (K80) gpm/psi1/2 or K8.0 (K115) sprinklers. The K5.6 (K80) sprinkler dates back to the early days of sprinkler protection. By comparison, ceiling sprinklers have evolved over the years and now have values as high as K25.2 (K360). By utilizing sprinklers that were originally designed to suppress fires from ceiling level, FM Global was able to dramatically alter its in-rack Data Sheet 8-9 guidance.
Fewer sprinklers, better protection
When protecting commodity hazards, current FM Global and National Fire Protection Association guidelines (NFPA 13), as well as other codes from around the world, require in-rack sprinklers to be installed on vertical increments ranging from 10 to 15 feet (3 to 4.6 meters). The guidelines also limit the maximum storage area above the top level of in-rack sprinklers to 10 ft. (3 m). Data Sheet 8-9 now allows for in-rack sprinklers to be installed on vertical increments ranging from 30 ft. (9.1 m) to as high as 40 ft. (12.2 m) depending on the commodity. In addition, storage heights above the top level of in-rack sprinklers can be as high as 40 ft. (12.2 m) depending on the commodity being protected and the ceiling-level sprinkler being installed.
"All the sprinkler research and innovation over the past 30 years has been focused on ceiling sprinklers. In-rack sprinklers have been pretty much ignored," explains FM Global's Weston Baker Jr., assistant vice president, senior engineering technical specialist. Baker works in engineering standards and oversees developments in this particular area. "We decided to leverage the relatively new ceiling-level sprinkler technology and apply it to the in-rack segment—and what we found was better performance at lower costs."
"We're kind of blowing the top off of everything we've done in the past."FM Global's Senior Research Engineer, Kristin Jamison
Baker said most of the research covering current in-rack system designs was conducted in the 1960s and 70s. FM Global itself did nearly 50 large-scale in-rack sprinkler tests from 1969 to 1976, which helped form the basis for today's in-rack sprinkler installation and design guidelines. Nearly all of those tests were conducted using small K5.6 (K80) sprinklers protecting short storage heights—25 to 30 ft. (7.7 to 9.1 m)—compared to today's standards.
According to Baker, FM Global began looking into the idea of applying new, larger sprinklers to in-rack solutions in the late 2000s. FM Global, he said, began to question if the knowledge base of in-rack systems was sufficient. The data was more than 40 years old and a lot had changed since those tests were conducted. Warehouses had gotten taller, the commodities being stored are quite different, and even the fire characteristics of cardboard and other storage materials have changed. So three years ago, FM Global launched a research project to optimize in-rack sprinkler design.
"We knew there had to be a better, simpler way to protect commodities in storage racks using in-rack sprinklers," Baker said. "So we committed three years, a lot of manpower, materials and time. It made sense to move forward because we knew the investment would really benefit our clients."
The goals of the project were to maximize vertical increments of the sprinklers, increase storage heights above the in-rack systems, allow for independent in-rack and ceiling design and reduce the likelihood of sprinkler damage. All of which would greatly reduce the cost of in-rack systems. To reach those goals, FM researchers needed to develop a new level of understanding of in-rack sprinklers and their role in fire suppression.
"The biggest questions we answered were, what is the critical amount of water needed to suppress a fire and what is the optimal flow rate and coverage area for in- rack sprinklers," Jamison said. "Those were unknown phenomena. Existing in-rack protection had never been optimized. So this really was a new approach. It had never been done before."
With those two pieces of information, obtained from extensive testing and modeling, FM Global was able to more than double the vertical increments of the sprinklers. At heights of 30 to 40 ft. (9.1 to 12.2 m), the higher K-factor in-rack sprinklers are able to suppress any fire that starts beneath them. This creates a virtual floor because, the testing confirmed, the ceiling sprinklers won't activate for any fire that starts below the top level of in-rack sprinklers.
The amount of storage space above the top level of in-rack sprinklers is now solely based on the capacity of the ceiling sprinklers. If the ceiling sprinklers can protect 40 ft. (12.2 m) of rack storage, for example, then a warehouse could have 40 ft. (12.2 m) of storage above the top-tier level of in-rack sprinklers.
And because modeling showed and testing proved that the in-rack system and ceiling sprinklers would not be needed at the same time, they can now be independent of each other. The in-rack sprinkler system designs offered in NFPA 13 and other fire protection codes assume that both the ceiling and in-rack sprinkler systems will be activated simultaneously, thus increasing the water supply needed.
Also, because fewer levels of in-rack sprinklers are needed, they can be deployed in a way that protects them from damage. With in-racks required every 10 to 15 feet under NFPA 13 and FM Global's previous Data Sheet 8-9, in-rack systems are susceptible to damage from forklifts and other equipment, resulting in leaks and water damage to the commodity being stored. The new guidelines allow for a design that eliminates the mid-bay face in-rack sprinkler, which is the most likely to be struck and damaged.
"We were able to confirm some things we already knew," Baker said, "and were able to learn a lot of new things, that if you stopped to think about, really make a lot of sense."
Greatly reduced costs
The impact of the new guidance on installation costs is impressive. FM Global asked two leading fire protection and sprinkler experts, S.A. Comunale and Wiginton Fire Systems, to compare costs of the new design and installation guidelines now offered in Data Sheet 8-9 to existing in-rack sprinkler protection schemes found in NFPA 13.
The two companies looked at the in-rack storage requirements for a hypothetical 500-foot by 1,000-foot (152-m x 305-m) storage facility with a storage height of 75 feet (23 meters) and a ceiling height of 80 feet (24.4 meters). The total cost of the project was US$2.11 million using the new FM Global option compared to US$3.57 million under the current guidelines, a reduction of 40 percent. Under the new FM Global guidelines, warehouse owners could save at least US$2 per square foot (.09 square meter) because of the reduced equipment and installation costs.
"Right off the bat, this new approach to in-rack sprinklers offers significant savings," said David Fuller, FM Approvals manager, fire protection. "There are other benefits as well. It will cost less to maintain, it is more environmentally friendly, there is a reduced potential for sprinkler damage from forklifts, and it offers better fire protection."
Fire modeling put to the test
The magnitude of the in-rack sprinkler research project was incredibly ambitious and would not have been possible without another equally ambitious project. A team of FM Global researchers, with help from scientists and academic institutions from around the world, had recently completed a five-year effort to develop cutting-edge, open source fire modeling software.
The software, named FireFOAM, integrates key physical models relating to fluid mechanics, heat transfer, combustion and multiphase flows. The software was the first to incorporate the complex relationship between fire and water when a fire suppression system is activated. The model can predict the impact a fire suppression system will have on a fire's fuel source and the fire's growth.
The software allowed for an innovative approach as researchers tackled the in-rack sprinkler project, coupling experimental science and fire modeling for the first time. Modeling allowed FM Global researchers to simulate multiple scenarios, sprinkler sizes and locations.
"When we started this project there were 13 open questions," Jamison explained. "Each one of those questions could have had its own series of large-scale tests. But through the synergy of modeling and experimentation, we were able to answer these questions with a fraction of the resources that would have been needed for the traditional approach. Modeling showed us where we needed to put the sprinklers, how to optimize the flow rate and hone all those parameters which were then validated through targeted large-scale testing."
A new understanding
Understanding the in-rack sprinklers' performance in the event of a fire was the biggest challenge. Jamison said they identified 11 parameters that affect the way the in-rack sprinkler interacts with a fire. Jamison and her team needed to determine which were the dominant parameters in order to optimize the in-rack system. They studied water flow distributions, ideal sprinkler positioning, and maximum vertical and horizontal spacing.
"We really had to key in on which of the parameters were most important and which were secondary," Jamison said. "We ended up focusing on the placement of sprinklers within the racks and optimizing the activation time and water coverage area. And for the first time, we understood what the parameters were that led to in-rack sprinkler success."
Unlike ceiling sprinklers, in-rack systems are dramatically affected by the commodity itself. Water distribution from ceiling sprinklers is unencumbered by the commodity and is much easier to predict. That is not the case with in-rack systems.
"One of the most important aspects of in-rack sprinklers is understanding, when a sprinkler is activated, where does the water go and how much water do you need to suppress the fire," Jamison said. "Water distribution out of an in-rack system is not uniform. The sprinkler might be only six inches away from the commodity so you get highly localized water concentrations and at four feet away you'll get no water at all."
To understand where the water goes, Jamison and her team conducted several water distribution tests and performed calculations using FireFOAM to determine optimal sprinkler placement and flow. By the time the team got to large-scale testing they had studied nearly everything associated with in-rack sprinklers. They looked at sprinkler activation, water distribution and suppression, activation time and the placement of face and flue sprinklers.
"Early on we tried some sprinkler configurations that just didn't work," Jamison said. "But by the time we got to the largescale tests, I would have been surprised if it didn't work the way we had expected."
Advancing fire protection
FM Global has a long history of working with the National Fire Protection Association to improve its fire codes, including NFPA 13. Eventually the recommendations of FM Global's Data Sheet 8-9 may find their way into NFPA 13 and possibly other fire protection codes. Baker and Jamison presented FM Global's findings at the annual NFPA Conference and Expo in June. And while the process of improving NFPA 13 will unfold over the next few years, FM Global customers will be able to utilize the new protection guidelines immediately.
"Section 1.5 of NFPA 13 indicates that you don't have to implement a protection scheme provided in NFPA 13 as long as you use a protection scheme equal to or better than what is offered in NFPA 13," Baker explained. "All of the research we conducted can be used by our engineering staff on behalf of our clients to assure local authorities that our in-rack sprinkler protection options meet the intent of this section so they can feel comfortable signing off, even though it's not in the code yet."