Published on February 27, 2023.

In Compliance

A quarterly overview of timely topics related to major NFPA codes and standards, written by NFPA engineers and other technical staff members 



Considerations for accessing roofs with photovoltaic systems installed

Amazon made headlines last year when it announced it was shutting down all rooftop photovoltaic (PV) systems installed on the company’s warehouses across North America after a series of fires. While the shutdown is a temporary measure designed to allow Amazon time to determine the root cause of the fires and determine next steps, it also prompts a deeper conversation about the risks associated with photovoltaic systems. 

Requirements for PV systems first appeared in the 2012 edition of NFPA 1, Fire Code®. Many of the requirements focused on ensuring firefighters were able to disconnect the PV system and still access the roof. While the requirements have evolved over the years, firefighter access and safety remain some of the key components of the roof-mounted photovoltaic system requirements in NFPA 1, and it is important to understand the code’s requirements for providing access to rooftops of buildings (other than one- and two-family dwellings) with PV systems installed.

Generally speaking, the code requires three types of pathways to ensure firefighters have the access they need to the roof for firefighting operations: perimeter pathways, other pathways, and pathways for smoke ventilation. The perimeter pathways provide firefighters with the ability to actually get on the roof.  The required width of the pathway depends on the length and width of the building. If either the length or width is greater than 250 feet (76 meters), then the pathway must be at least 6 feet (1.8 meters) wide. If the length and width of the building are both 250 feet or less, then the pathway must be at least 4 feet (1.2 meters) wide. Regardless of the width, the perimeter pathway must be provided along all edges of the roof.
The “other pathways” exist to ensure firefighters have access to different points on the roof that are necessary for them to conduct their operations, such as to ventilation hatches and roof standpipes. They also allow firefighters the opportunity to move from side to side on the roof without having to follow the perimeter pathway. The other pathways consist of three different requirements. The first is to provide a straight-line pathway that is at least 4 feet wide to all ventilation hatches and roof standpipes. The second is to provide a pathway at least 4 feet wide around every roof access hatch. In addition, another pathway at least 4 feet wide must be provided from each roof access hatch to either the parapet or roof edge. The last component requires pathways be provided at least every 150 feet (46 meters) throughout the length and width of the roof. The width of these pathways will depend on which smoke ventilation option is chosen. Although the Fire Code does not explicitly state a maximum PV array size, this pathway requirement has the effect of limiting a PV array to no larger than 150 feet by 150 feet, or 22,500 square feet (2,116 square meters).
The final aspect of firefighter roof access deals with two requirements for smoke ventilation. The first requires a pathway that is at least 4 feet wide around all sides of nongravity smoke and heat vents. For gravity-operated smoke and heat vents, a minimum 4-foot pathway is still required but only on a minimum of one side. The second requirements deals with ventilation options between array sections. There are three options, but only one must be provided. The first option is that the pathways between the arrays are at least 8 feet (2.4 meters) wide. The second option is to provide a minimum of a 4-foot pathway that borders existing roof skylights that are spaced no more than 150 feet apart throughout the length and width of the roof. The third option is to provide a minimum 4-foot pathway that borders venting cutout options every 20 feet (6 meters). The venting cutout options must be 4x8 feet.

A number of changes were made to the PV system requirements for the 2021 edition of NFPA 1. One of those was the addition of figures in the annex depicting the pathway requirements covered above. If an incident does occur in a building with a PV system installed on the roof, these pathways are vital to ensuring that firefighters can not only access the roof but can also carry on their operations as they normally would.

Valerie Ziavras is technical services engineer at NFPA.




Understanding low-frequency alert signals and occupant notification

Recent changes to NFPA 101®, Life Safety Code®, require the use of a low-frequency alert signal to wake sleeping occupants in the event of a fire. These changes, based on research completed over the last 20 years, show that a 520 Hz signal has superior wakening effectiveness compared to a traditional 3,000 Hz signal for high-risk segments of the population, including people with hearing loss, people over the age of 65, school-aged children, and people who are alcohol-impaired. With these changes, however, it is important to note the difference in requirements between the Life Safety Code and NFPA 72®, National Fire Alarm and Signaling Code®, when it comes to the use of a low-frequency alert signal.
First, we need to understand the difference between single-station and multiple-station smoke alarms and a fire alarm system. This is a key point, because the requirements for the use of low-frequency alert signals in NFPA 72 are different for a whole fire alarm system and single-station or multiple-station smoke alarms. In general, a fire alarm system consists of a control unit and initiating devices such as smoke detectors, and achieves occupant notification by using notification appliances such as strobe lights and speakers. A single-station smoke alarm is a self-contained unit that consists of a smoke sensor and all the power, circuitry, and speakers needed to achieve occupant notification through an audible signal and is typically used in residential occupancies. When multiple single-station smoke alarms are interconnected, they are considered multiple-station smoke alarms.
Chapter 29 of NFPA 72 covers the performance, selection, installation, operation, and use of single-station and multiple-station alarms. Since 2010, the code has required that single- and multiple-station alarms installed in areas where the occupants have mild to severe hearing loss utilize a low-frequency alert signal. Chapter 18 of NFPA 72 covers the design and installation of fire alarm system notification appliances, which provide occupant notification for a fire alarm system. Since 2013, this chapter has required that audible notification appliances create a low-frequency alert signal in all occupant sleeping areas.
Changes in the 2021 edition of NFPA 101 require that, where the occupancy chapter mandates their use, both audible alarms in sleeping rooms initiated by the fire alarm system or created by single-station or multiple-station smoke alarms must result in a low-frequency 520 Hz alert signal. Two of the residential occupancy chapters in NFPA 101—new hotels and dormitories, and new apartment buildings—now require the use of low-frequency alarms for audible notifications activated by both single-station and multiple-station smoke alarms and the fire alarm system.

The difference between the NFPA 72 requirements and the 2021 NFPA 101 requirements is that NFPA 101 now requires, where mandated by the occupancy chapter, that all audible alarms in sleeping areas be a low-frequency 520 Hz alarm regardless of the hearing capabilities of the occupants in that sleeping room. NFPA 72 would only require low-frequency single-station or multiple-station alarms in those areas if the occupants had mild to severe hearing loss, or low-frequency alarm signals if the building contained a whole building fire alarm system.

A challenge with low-frequency alarms is that they require a speaker to produce the lower frequency instead of the tone generator used to create the traditional high frequency. Speakers require more electrical power, a feature that has made the development of low-frequency battery-operated single-station or multiple-station smoke alarms more difficult. The Fire Protection Research Foundation conducted a project on audible alarm signal waking effectiveness and found that there are currently no listed smoke alarms capable of emitting that sound available on the market.
But alternative solutions exist. One is to use smoke detectors with integral sounder bases connected to a building fire alarm system instead of standalone single- or multiple-station smoke alarms. Another option is to use system smoke detectors with fire alarm system horns, or utilizing system smoke detectors with speakers from an in-building fire alarm emergency voice alarm communication (EVAC) system. All of these can be used until a listed smoke alarm capable of producing the 520 Hz alert signal comes on the market.

Shawn Mahoney is a technical services engineer at NFPA.



Fire prevention through proper electric vehicle charging installation and maintenance

The continued influx of electric vehicles (EVs) into the market is generating a variety of safety questions. At NFPA, we’ve received an array of recent questions related to the safety of EV charging installations. While there are likely to be many updates to codes and standards as we understand more about the topic and the related technologies, we must still use what we have available to us now to provide safe installations that protect people and property. 

It is no secret that poor electrical installations and improper usage of electrical equipment contribute to a high number of annual fire statistics. On the other hand, ensuring proper installation and maintenance of EV charging stations, typically referenced as electric vehicle supply equipment (EVSE) in codes and standards, is a great starting point for fire prevention. EVSE is utilized specifically to charge the vehicle itself. It is important to note this, because there is other EV equipment available that permits power to export from the vehicle back to the premises wiring system. Equipment that has the ability to both charge the vehicle and induce power back to the premises wiring from the vehicle is commonly referenced as bidirectional EVSE. Regardless of the type of equipment utilized, proper installation and maintenance is a critical piece in fire prevention.
 From an EVSE installation perspective, the manufacturer’s instructions and Article 625 of NFPA 70®, National Electrical Code® (NEC®), provide many of the requirements necessary for safe installation. The scope of Article 625, Electric Vehicle Power Transfer System, covers the electrical conductors and equipment connecting an electric vehicle to premises wiring for the purposes of charging, power export, or bidirectional current flow. Part III of Article 625 is specific to installation. Some of the key requirements include:
• Each outlet that supplies EVSE rated greater than 16 amps or 120 volts must be supplied by an individual (dedicated) branch circuit. In cases where an energy management system is utilized to manage the EVSE load or where the EVSE has adjustable ampere settings, multiple EVSE maybe served from a single branch circuit. 

• EVSE that is rated more than 60 amps or more than 150 volts to ground must have a readily accessible disconnecting means installed. 

• The point of connection coupling means, which is used to connect the EVSE to the vehicle itself, must be installed 18 inches above the floor level for indoor installations and 24 inches above grade level for outdoor installations. 

• All receptacles installed for the connection of EVSE must include ground-fault circuit-interrupter (GFCI) protection. 
When it comes to preventative maintenance of EVSE, the latest edition of NFPA 70B, Recommended Practice for Electrical Equipment Maintenance, provides helpful information. Chapter 34 of NFPA 70B specifically covers electric vehicle charging systems. One major component of NFPA 70B is that where EVSE is installed, a maintenance program should be developed and utilized for it. The EVSE maintenance program should be planned at the time the system is installed to ensure the greatest level of safety to the maintenance worker and the highest level of reliability and safety to the user and operator of the vehicle charging station. It is important to note that only qualified persons should perform maintenance on EVSE. Due to weather and the potential for physical impact, cords, charging connectors, and mounting of the EVSE should be regularly inspected and maintained.
 Many recent questions around EV charging installations were specific to parking structures, and NFPA 88A, Standard for Parking Structures, is a great resource. It requires that all installations of EV charging equipment comply with NFPA 70. While NFPA 70 requires all EV charging equipment to be listed, it does not provide specific details around listing. NFPA 88A, on the other hand, provides those details, requiring that: 
• Electric vehicle charging stations must be listed and labeled in accordance with UL 2202, Standard for Electric Vehicle (EV) Charging System Equipment.

• Electric vehicle charging system equipment must be listed and labeled in accordance with UL 2594, Standard for Electric Vehicle Supply Equipment.

• Wireless power transfer equipment for transferring power to an electric vehicle shall be listed and labeled in accordance with UL 2750, UL LLC Outline of Investigation for Wireless Power Transfer Equipment for Electric Vehicles.
The best method of fire protection for EV charging equipment installations is fire prevention. This can only be achieved if the equipment is both properly installed and properly maintained. That means that the process is always ongoing, and that is where having a proper maintenance program in place will help reduce potential risk. As we all travel this new road of EV charging equipment installations together, it is important that we look out for one another and keep it between the lines—especially from a safety perspective. 

Corey Hannahs is technical services engineer at NFPA.



Understanding and applying the concept of miscellaneous storage to sprinkler systems

A common question NFPA technical staff gets is about when and how to apply the miscellaneous storage concept in NFPA 13, Standard for the Installation of Sprinkler Systems.
The concept, first introduced in the 1991 edition of NFPA 13, continues to be misunderstood and is often misused by fire sprinkler designers, engineers, contractors, building owner representatives, and inspectors. Recent fire losses show how storage can challenge a fire sprinkler system, and the provisions of miscellaneous storage help walk the fine line between the installation of a costlier, more robust storage sprinkler system and a more common, less expensive fire sprinkler system. To utilize the concept properly, though, it is important to understand what miscellaneous storage is and when it should be applied, as well as the storage height limitations, pile size limits, and pile separation requirements.
The first step in the process of utilizing the miscellaneous storage concept is understanding what miscellaneous storage is. The 2022 edition of NFPA 13 defines miscellaneous storage as “storage that does not exceed 12 feet (3.7 meters) in height, is incidental to another occupancy use group, does not constitute more than 10 percent of the building area or 4,000 square feet (370 square meters) of the sprinklered area, whichever is greater, does not exceed 1,000 square feet (93 square meters) in one pile or area, and is separated from other storage areas by at least 25 feet (7.6 meters).” This definition presents the five requirements of miscellaneous storage and allows designers, engineers, or building owner representatives to decide whether to employ the concept of miscellaneous storage.
The key phrase in the definition of miscellaneous storage is that the storage “is incidental to another occupancy use group.” The concept of miscellaneous storage was first introduced to allow for situations where small groups of storage that are secondary, but essential, to the general occupancy, without increasing or upgrading the fire sprinkler system demand for that occupancy. Thus, if the facility requires small amounts of storage of raw materials to allow for ready use in regular operations, it may be correct to use the miscellaneous storage concept. An example of this would be a car showroom that contains a small display of tires.
Before deciding on whether using the concept is appropriate, it is important to understand the four storage limitations that are specified in the definition of miscellaneous storage, starting with storage height. With storage arrangements that exceed the height limitation of 12 feet (3.7 meters), the major concern shifts from horizontal fire spread to vertical spread, and the storage height limitation ensures that a limited quantity of storage does not overwhelm the fire sprinkler system. The 4,000-square-foot limitation on the total amount of allowed storage “is derived by taking 10 percent of the maximum allowable area of coverage for a sprinkler system riser protecting high-piled storage,” according to NFPA 13. Limiting the storage area minimizes the possibility of a fire in that area from rapidly spreading and overpowering the surrounding fire sprinkler system in areas of lower hazard.
The standard’s limitation on storage piles exists to further ensure that a fire in the storage area cannot overwhelm the fire sprinkler system. A common mistake, though, is that storage piles often exceed the 1,000-square-foot (93-square-meter) area limit.Additionally, it is important that those storage piles are separated by at least 25 feet (7.6 meters) from other storage piles, which greatly reduces the risk of heat from a fire in one storage pile from starting a fire in an adjacent pile.

Once the definition of miscellaneous storage is understood, the protection criteria can be found in Table of the 2022 edition of NFPA 13. The system designer can evaluate if the occupancy fire sprinkler system is sized and designed adequately to protect the planned miscellaneous storage. In many cases, a less costly sprinkler system, designed for a nonstorage occupancy, can provide a reasonable degree of protection for life and property from fire when the miscellaneous storage concept is utilized properly. 

Tom Goss is a senior specialist at NFPA.