Where The Green Things Are
Home to gardens, photovoltaic arrays, wind turbines, and more, rooftops increasingly host some of the most popular innovations of the green movement. And that’s what concerns the fire service and the code community.

NFPA Journal®, November/December 2009

By Alan R. Earls

If you want to see the future of "green" rooftops, you need to travel to Stuttgart, Germany, where roughly a third of the flat roofs in the city are green, literally, because they’re covered with specially selected plantings.

Stuttgart may be out front, but according to green-roof advocate Robert Berghage, an associate professor of horticulture and director of the Center for Green Roof Research at Pennsylvania State University, a lot of other cities around the world, including some in the U.S., are racing to catch up. "When I first started here 10 years ago, you could count the green roof projects [in the U.S.] on your fingers and probably not even need to use your toes," says Berghage. By contrast, he says, green roofs are now being built at an unprecedented rate, with many municipalities — New York, Chicago, and Portland, Oregon, among them — implementing legislation to encourage or even require green roofs on certain kinds of new construction.

While the exact number of these projects is difficult to pinpoint, a recent report issued by Green Roofs for Healthy Cities (GRHC), an advocacy group, claims an increase of 35 percent in the number of green-roof projects completed in the U.S. in 2008 compared to 2007, for a yearly total of 3.1 million square feet. The overwhelming majority of those projects were either commercial or institutional structures.

The term "green roof" covers a multitude of technologies and design philosophies, but it’s primarily intended to evoke Berghage’s vision of the abundant plant life that is so common on Stuttgart rooftops. Advocates say these green roofs, more properly called vegetated roofs, can help reduce a building’s carbon footprint by offering extra insulation, absorbing storm-water runoff, and freshening the air.

The term also covers rooftops that host photovoltaic (PV) arrays, or even wind turbines. In optimal situations, PV roofs can generate all the electricity a building needs, and sometimes more, reducing the need for energy created by burning fossil fuels and providing savings on utility costs. While some PV roofs began to appear as far back as the 1970s, rising energy costs, the availability of lower-cost and higher-performance PV systems, and government incentives have all combined to boost their popularity.

But popular doesn’t necessarily mean safe. PV systems, for instance, have been involved in building fires around the country. For instance, in October of 2002, the San Jose Mercury News reported that fire investigators had determined that a residential PV unit malfunction, the exact nature of which could not be determined, had sparked a substantial wildfire that eventually covered more than 3,000 acres and affected 35 homes. More recently, a fire involving PV systems in Sedona, Arizona, exposed a firefighter to a severe electrical shock (see "Case Study: PV Shock," page 54).

Vegetated roofs pose fire- and life-safety issues as well. While insisting that thousands of green roof systems have been trouble-free, Steven Peck, GRHC president, acknowledges that at least one vegetated roof in Germany collapsed because a drainage system failed to operate properly. Furthermore, experience with conventional buildings shows that inadvertent roof overloading with snow, water, and ice is already an important safety problem, even without the complication — and the significant weight — of extensive plantings.

Those issues concern Allan Fraser, senior building code specialist for NFPA and a former municipal building inspector. Fraser points out that, while vegetated roofs can be, and regularly are, built in compliance with existing codes, that doesn’t mean they’re necessarily safe. In most cases, he says, the issue is loading, or potential loading. Designers, Fraser says, need to plan for the dead load—the weight of the roof itself—while planning ahead for the live load, which includes people, snow, vegetation, water, electrical equipment, and anything else that might one day reside there, not to mention the increased risk of collapse in the event of a fire. "Codes address these issues, but designers and code officials really need to understand how all these factors can interact or how they might change over time," Fraser says. In other words, a green roof is a dynamic system, and it’s not always clear how things might work in the real world—and there’s no body of experience indicating how to monitor green roofs over time.

As Fraser points out, factors of change and neglect could lead to under-maintained vegetated roofs accumulating dead or dry plantings, thus providing a highly combustible fuel source. Similarly, with PV arrays, Fraser says products and installations are usually delivered ‘after-market’ rather than as an integral part of the design and permitting of the building. As a consequence, PV installations may end up putting dangerous point loads (such as the supports holding up PV arrays) on rooftops that exceed the maximum loads specified per square foot for the structure. Similarly, high winds can potentially lead to the uplift and failure of PV arrays.

The code-related gray areas created by green roofs are of growing concern to the code and building communities, as well as to the fire service. "Over the past 100 to 150 years, we have gone through an evolution from poorly built buildings of all types to the almost universal practice of building by code," says Curt Varone, NFPA’s director of Public Fire Protection. "Now, though, in addition to the challenges we face with modern lightweight construction, we also have green buildings to contend with."

Managing new kinds of risk
Photovoltaic panels themselves are especially worrisome to Varone. Aside from their potential for interfering with firefighting operations, there is the problem of controlling the electricity they generate, particularly when there is a fire in an adjacent area. Although some have suggested simply covering the PV systems with an opaque tarpaulin to deenergize them, Varone says that can be hard to do in the midst of an emergency and is not recognized as a reliable way to make the systems safer to handle.

"Their presence on the roof and the difficulties of working around them impact what is traditionally one of the most important elements in firefighting tactics—establishing ventilation through the roof to allow combustion and heat out and to improve victim survivability," Varone says. "Plus, when PV modules and panels are exposed to sunlight they generate electricity, and there isn’t much that can be done about that. It isn’t something you can just switch off. We have to look at this as a new kind of risk, and we need to train firefighters about how to manage that risk."

Code and building professionals are accustomed to playing catch-up on the safety impacts of such innovations, green roofs among them. Robert Solomon, NFPA department manager for building and life safety codes, says there are no national standards that regulate green roof design, but adds that groups like ASTM International (formerly known as the American Society for Testing and Materials) and the National Roofing Contractors Association (NRCA), along with companies like the insurer FM Global, are in the process of releasing new design criteria for such systems. Solomon says NFPA is taking a "measured approach" to the rooftops issue, identifying concerns and problems as well as possible code solutions; those solutions can be existing documents from NFPA or elsewhere, Solomon says, or they can be new documents that will have to be developed by one or more NFPA Technical Committees.

NFPA has identified a number of codes and standards that already manage some of the issues associated with green roofs, Solomon says, including NFPA 5000®, Building Construction and Safety Code®. According to Solomon, several areas within NFPA 5000 can help NFPA address these topics, including the goals and objectives in Chapter 4 of the code. For example, the broad goals of "public welfare" in Section 4.1.6 include a provision that "the design, construction, and operation of the building is consistent with the reasonable expectations of society with respect to energy efficiency, cultural heritage preservation, mission continuity, and environment." The specifics of how this is addressed, however, and where it gets addressed in the code, have yet to be determined, but Solomon says Chapter 38, "Roof Assemblies and Roof Structures," in NFPA 5000 is a good starting point. He notes that the requirements of this chapter describe a roof design that protects the interior of the building from the elements and provides a substantial base that can support the weight of other structures (such as a penthouse, a mechanical equipment room, or antennas) while specifying that the construction materials used do not present an increased fire hazard. Underlying these provisions is the understanding that anything that ends up on the roof cannot diminish any of these objectives, and that any components or substructures must be securely tied into the roof so they cannot become airborne in high winds.

Solomon says any vegetated roof system or design will have to be evaluated for a number of factors. Among these are the materials used, with the provision that they cannot become airborne in high winds, which could damage the host building or adjacent structures or injure people at street level. The containment systems for the vegetation must likewise be securely anchored. The contributed weight factors associated with the containment system, the soil, and the vegetation itself must be evaluated. In a worst-case scenario, the added weight of water that collects in the soil, either from a rain occurrence or during firefighting operations, must be accounted for. At a weight of 8.3 pounds per gallon, several hundred gallons of water can quickly add up to tons of additional weight that most roofing systems are not designed to handle. The third area of concern is what happens if the vegetation dies off, in which case the roof could be host to a very dry, highly combustible fuel package not normally present.

Many of the same concepts also apply to PV arrays, such as anchoring of the arrays and conduit; accounting for the weight of the system array; and considering the fire-hazard properties of the composite materials that might be used to form the actual PV modules and panels. Article 690 of NFPA 70®, National Electrical Code®, is entitled "Solar Photovoltaic Systems," and provides electrical designers with the requirements to provide a safe and functional PV system. With regard to first responders, Solomon says NFPA and other organizations have issued alerts to make sure firefighters are aware that even though the electrical power from the utility can be isolated, electrical energy (up to 600 volts) is still present as long as the PV array is connected. The NEC criteria require a special disconnecting means for the PV array, but fire department preplanning is essential to know what buildings have PV systems and to know where that disconnect feature is located.

In addition, Mark Earley, chief electrical engineer at NFPA, says a new rooftop-related article has also been proposed for the 2011 NEC. "It would have requirements similar to the solar article, number 690," he says, and could also deal with "lifecycle" issues for PV systems, such as the need for periodic removal and reinstallation of arrays when roofs are resurfaced. "The bottom line is the PV arrays are electrical entities that need to be professionally installed by people with some knowledge of NEC requirements," Earley says.

Solomon says other ideas include the formation of an NFPA advisory committee on energy and green design issues. Such a group, Solomon says, would help NFPA sort out the appropriate areas for the organization to address in its codes and standards development area. He says the organization is also discussing the possibility of holding a green-related session at the NFPA Conference & Expo® in Las Vegas next June, with topics ranging from Leadership in Energy and Environmental Design (LEED) certification and fire protection to training strategies for first responders who encounter PV arrays.

Steven Peck, of GRHC, says builders of vegetated roofs in the U.S. and Canada have so far looked primarily to the German FLL standards. (FLL in translation is called The Landscaping and Landscape Development Research Society.) FLL has produced design guidelines for issues such as plantings and drainage. Based on FLL data, Peck says, "A green roof will actually reduce the threat of fire because extensive green roof systems have a large degree of aggregate material, most of which is expanded shale, clay, and vermiculite, which does not burn." Likewise, healthy plants are largely resistant to fire, Peck says. "They don’t really burn, they shrivel," he says. "There have been some green roofs that have caught fire, but in every case it was because of a lighted cigarette and only in the presence of dried grasses."

However, warns Fraser, if you look historically at building failures or fires, the vast majority are traceable to enforcement or compliance issues; the problem "is rarely the code itself," he says. Still, he adds, some of the potential danger in green roofs can be addressed by writing more specific language into codes to deal with evolving design practice, such as what’s provided by FLL.

The industry responds
Meanwhile, faced with the need to keep their members safe, two roofing industry groups, working in cooperation with green advocates, have gotten involved in the issue. According to Linda King, managing director of the Single Ply Roofing Institute (SPRI), her organization is working with Peck’s group to devise "The Wind Design Standard for Vegetative Roofing Systems" and "The External Fire Design Standard for Vegetative Roofs," standards King hopes will eventually become part of the International Code Council’s International Building Code. While there is general agreement among the groups that a standard is necessary, King says, the particulars of what should be included in such a document have yet to be determined. For example, although vegetative roofs have been used in Europe for a long time, there is little test data on their performance under high wind or fire conditions. Not surprisingly, roof system manufacturers, roofing contractors, building code representatives, and suppliers of the vegetative systems all have their own perspectives on what should and shouldn’t be included in a standard. "Those standards are being balloted, and we are making progress toward handling the objections that you might expect a first-time standard would produce," King says.

Mark Graham, technical director at the NRCA, is concerned that the standards, proposed or otherwise, are not scientific enough. "There is definitely a need for the roofing industry to test" green roof materials and systems, he says. This past summer, NRCA sponsored wind-tunnel testing at Southern Illinois University to establish fundamental research relating to wind resistance of vegetated roofs. Concerns include both the possibility of roof uplift, particularly if a vegetated roof becomes dry and provides less weight on underyling roofing material, and the possibility that green roof material—vegetation and substrate—might become airborne. Graham says the work was completed in August and the results are still being analyzed.

Similarly, the insurer FM Global has initiated a green-roof fire-testing protocol it calls "Approval Standard for Vegetative Roof Systems." "We got into this because our building-owner customers asked us to, and because manufacturers of roofing systems asked us," explains George Smith, assistant vice president and director of FM Approvals, the product certification unit of FM Global. Smith says work started on the standard in April, and that a draft has been circulated within the industry. He expects it to be approved and finalized by the end of the year. Other insurers are taking a closer look at the issue, too. According to a report in the Journal of Commerce, a Canadian construction industry periodical, last year the UK branch of the Swiss insurance company Zurich announced that it now considers vegetated roofs to be a potential fire hazard, and that it will be more cautious when considering insuring such structures.

While the building and code communities look for ways to make green roofs safer, people across the country are becoming more interested in bringing a bit of greenness to their rooftops, especially in California, where both vegetated roofs and rooftop PV arrays are increasingly popular. A May press release from the office of California Governor Arnold Schwarzenegger notes that "California leads the nation with over 500 megawatts of installed solar at 50,000 different installations [and] has more than 60 percent of the nation’s installed solar photovoltaic capacity." But according to a 2009 report by the Global Solar Center, an industry website, while California continues to be the leader in total solar installations, incentive programs around the country are helping other states narrow that lead.
While that growth is spurring the code community to take a harder look at the related fire- and life-safety issues, Fraser offers a cautionary reminder that the code process moves slowly, especially compared to a marketplace trend that’s suddenly seen as fashionable or otherwise desirable. "When you begin to change a code, it can still take six to 10 years before the change is reflected in new construction practice," Fraser says. But with research and training efforts related to green roofs on the rise, safety experts hope that the right message can be conveyed to the design and enforcement communities: plant your trees or install your PV arrays, but build and monitor them with safety in mind. The greenest rooftop is the safest rooftop.

Alan R. Earls specializes in technical and safety topics and is based in Franklin, Massachusetts.

SIDEBAR
Case Study: PV Shock

According to Terry Keller, assistant chief of the Sedona, Arizona, Fire District, one of his firefighters had a potentially deadly encounter with a photovoltaic system while trying to extinguish a home fire.

According to information provided by Keller, the incident occurred June 10, 2008 at a 2,500-square-foot residence where a roof-mounted three-kilowatt PV system had recently been installed. The fire, which was later determined to have been started by an electrical cord under a bed, was "well established" when firefighters arrived. Once the main fire was knocked down, a smaller hand line was being operated by a few firefighters in the fenced backyard. According to Keller, one of the firefighters was sent back to the truck to retrieve a pike pole. On his way, he reached up and used his wet, gloved hands to grasp the top of the two chain-link fence posts on either side of the open gate. When he made contact with both posts, he was knocked to his knees by an electrical shock. Although he was able to recover his footing, he was transported to a local emergency room suffering from weakness and EKG changes. He returned to full duty the following day.

Although both metered service from the electrical grid and from the PV system were secured prior to the firefighter's electrocution, department investigators believe that the conduit that housed the feed from the PV system on the roof, which ran along and under the eave line of the flat-roof structure, failed at a fitting where it negotiated one of the building corners. The supports for this metal conduit also failed, and allowed the melted and exposed wires to rest on top of the chain-link fence, which energized the fence with voltage from the PV array.

Following this incident, the Sedona Fire District conducted training on PV system dangers. "We want to share this information as widely as possible," adds Keller.

- Alan R. Earls

SIDEBAR
Fuel is Fuel
Responding to the fire service challenges of alternative energy

NFPA and the Fire Protection Research Foundation (FPRF) are working to address some of the challenges emergency responders face when they encounter alternative fuel sources in the field. Three research projects-two ongoing, and one just completed-illustrate the range of that work.

"Reaching the U.S. Fire Service with Hydrogen Safety Information: A Roadmap" was funded through the U.S. Department of Energy and the National Renewable Energy Laboratory, and the final report was issued in September. (To download a copy, visit www.nfpa.org/foundation.) This study provides an overview of the U.S. Fire Service to help improve the transfer of hydrogen safety information to and from the emergency response community. In particular, the report provides a roadmap of regulatory permitting and fire-service emergency response, and focuses on applicable new hydrogen-based applications, including hydrogen refueling stations and hydrogen back-up power installations such as those found at telecommunications facilities.

"Fire Fighter Safety and Emergency Response in Pre-Planning and Fireground Tactics for Alternative Energy Technologies" is one of two new projects just getting underway that involve the fire service and alternative energy. The project will study firefighter safety in the context of the widespread introduction of electric drive and electric hybrid vehicles, with a specific focus on emergency response to vehicle fires and accidents, including within structures, such as charging or docking applications. It will also study firefighter safety related to structural firefighting in the presence of solar (photovoltaic) panels.

The goal of the one-year project is to assemble and disseminate best-practice tactical information for firefighters and fireground incident commanders when responding to emergency events. Funding is provided by the U.S. Department of Homeland Security (DHS) and Federal Emergency Management Agency (FEMA) through a Fire Prevention & Safety Fire Grant.

"Emergency Responder Training for Advanced Electric Drive Vehicles," also just getting started, is part of a major recent federal initiative to accelerate the manufacturing and deployment of electric drive vehicles. To be effectively prepared for the widespread implementation of electric drive vehicles, emergency responders need accurate and timely training materials. As a result of this program, emergency responders will be able to safely manage incidents involving advanced electric vehicles. The goal of the project is to provide comprehensive awareness and emergency response training to the more than 1.1 million members of the U.S. fire service. This is a large, three-year project funded by the U.S. Department of Energy.

Alternative energies hold great potential to improve our world. It's important that we continue to work closely with the emergency response community to make sure we address its interests and concerns.

- Casey C. Grant, P.E., is program director of the Fire Protection Research Foundation.