By JOSEPH C. CAMAROTA
When responding to a structure, residential, or commercial fire that involves solar photovoltaic (PV) systems, you must implement a new firefighting strategy. No longer can the operating incident commander (IC) open the main electrical disconnect to a structure and feel comfortable that no energized power sources will remain. Solar PV systems are always energized. The overall firefighting tactics and strategies employed must be adapted to handle this technology.
|(1) An atypical disconnect switching scheme with solar PV identification. (Photos by author.)|
For command personnel to effectively formulate solar PV standard operating procedures (SOPs), leadership must first understand the basics of a solar PV system and its associated operation. Once ICs grasp the basics of this operation, they can formulate safe and reliable solar PV system SOPs. The key to formulating any solar PV SOPs is to approach the system with the intent of isolation rather than disconnection.
Solar PV systems generate electricity from the sun, delivering the power generation back to a host system. In residential and commercial applications, the point of common coupling (POCC)-the point at which the solar PV is connected to the building’s electrical system-is located behind the utility meter. This system’s integration is achieved through either a reverse feed circuit breaker at the house panel, a bus tap, or at the switchgear serving a commercial building. In any case, the electricity generated from the solar PV system is “reverse fed” into the building’s electrical system.
Electrical Power Generation
A solar PV module is the mechanism that generates solar electricity. A module is made up of either monocrystalline or polycrystalline cells. The difference between the two is related to the method of manufacture, physical appearance, size, efficiency, and price point. When collected together, multiple modules connected in series or parallel are identified as an array.
Arranging modules in multiple strings and back to an inverter drives the system’s voltage. According to the parameters set forth in the National Electrical Code®, a solar PV system’s voltage can reach 600 or 1,000 volts of direct current (vdc). Various code making panels are now considering allowing systems of 1,500 vdc.
The power generated by an array (or a group of arrays) is carried back to the POCC through an inverter by a conduit and wire or cable tray system. The inverter can be one of three types: micro-inverter (handles individual modules), string (transformer-less), and central (having isolation transformers and using combiner boxes). Inverters convert the direct current (DC) to alternating current (AC). Regardless of opening up the AC disconnect, the DC side of the inverter will always be energized. Hazardous voltage will always exist throughout the DC system.
Following are several of the many types of solar PV systems. Each has its own hazards that first responders must keep in mind.
- Ballasted rooftop. The additional weight of ballast block, conduit, wire, and cable tray could produce an accelerated roof collapse in a compromised structure. It may also impede ventilation.
- Penetrated rooftop. Concerns for first responders include weight and ventilation.
- Ground mount (either ballasted or post-driven). They are susceptible to vegetative/brush fires. Hazards to first responders could also include bee/wasp nests or snakes that take up residence around the system.
- Parking canopy. A car fire taking place here can compromise the solar PV system and structure.
- Building integrated. “Solar shingles” (roof shingles that generate electricity) pose a hidden danger within the bullring’s roof structure.
Again, once your fire department grasps the configuration of the various solar PV systems and their associated operations, you can form effective SOPs.
Building and fire officials should establish communications between agencies; it is essential for creating an inventory of properties featuring solar PV systems within their jurisdiction. Once created, include the inventory in your preplan “toolbox.” The inventory is useful information only when used. Conduct site visits and training exercises with the properties you identify to deal with the systems present at an emergency. In addition, compile an “on call” list of available experts such as solar providers, electrical contractors and engineers, and other similar professionals to lend technical expertise if needed.
With all the preplanning done in the fire service, there is no guarantee that first responders will never encounter an unidentified system on the fireground. If, during their 360° size-up, arriving units identify electrical components that seem abnormal to an electrical system, chances are they may be dealing with a solar PV system. Conduits, inverters, disconnects (switches that are associated with the solar PV system), and switching schemes are all components that may indicate the presence of solar PVs.
In the state of New Jersey, recent legislation was passed that requires commercial structures to display a placard-similar to a truss sign-at the entry that identifies the building as having a solar PV system. Residential structures are exempt.
As soon as crews acknowledge that a solar PV system is present on the fireground, they must notify the IC. Once identified, the incident command system’s (ICS’s) utilities group should locate and open all disconnects sequentially. When opening all disconnects, implement lock-out/tag-out procedures. Notify the IC once again on completion of this operation.
|(2) Rooftop solar PV components.|
When you open the AC disconnect, the inverter will shut down [this is a Nationally Recognized Testing Laboratory (NRTL) listing requirement]. The DC side will remain energized; it will always be “hot” because the solar modules will continue to generate electricity. During daytime (sunlight) and nighttime (scene lights/exposure fire), the solar modules will always be capable of generating hazardous voltage levels.
Also of particular concern are solar PV systems that serve battery storage. This type of system employs not only solar PV but also a charge controller and battery system. The power from the solar modules charges the batteries, which in turn serves the house. Once there is a power failure, the batteries will continue to serve select household loads. If the utility power comes back and the batteries are fully charged, the solar PV system will revert to serving the utility grid in the back feed situation. In any event, the utilities group must consider additional power sources and isolation procedures on discovering a solar PV system.
All systems’ components should be labeled. However, this may not always be the case. First responders should be aware of the fact that, despite labels being a code requirement, they could be missing, weathered, or generally unreadable.
Recent code changes have come into effect with regard to firefighter rapid shutdown. These isolation techniques will provide isolated areas to allow the IC and firefighting personnel to readily identify electrified areas and their associated hazards.
If the solar PV system is the source of the fire, a concern exists after any life hazards are mitigated. So, use a dry chemical extinguisher on any energized components. If roof material is on fire, NRTL testing shows that using a 20° to 30° fog pattern at 100 pounds per square inch will not result in an undue shock hazard. These studies have also found that applying a fog pattern reduces the electrical current below the perception level.
If you encounter a structure fire, implement structural firefighting techniques. During these operations, ICs and firefighting personnel should be conscious of the existence of the solar PV system.
|(3) Rooftop solar PV components.|
Once you isolate the system, remove the PV modules only under special circumstances (i.e., the presence of a life hazard). If they must be removed, personnel should do so using only nonconductive tools.
There has also been much discussion about Class A foam, which can be effective for extinguishing fires involving solar PV. It can form a blanket underneath the arrays in areas where water cannot be directly applied. Although you can use foam as an extinguisher, it can have conductive properties similar to water. Never use foam in an attempt to block light from reaching a solar PV module; you cannot rely on it as a means of eliminating power generation.
When performing a size-up and planning for ventilation operations, the IC should consider the location and size of the solar PV arrays. During cutting operations, take considerable care to avoid array conduit and wiring.
For residential ventilation operations, firefighting personnel must be aware that solar PV conduits may run in the attic space. The National Electrical Code® requires solar PV conduit/wiring systems to be installed more than 10 inches from the roof deck or sheathing. The only exception to the rule is that these conduit and wire systems can be installed less than 10 inches when they are directly under the array. However, firefighters should still proceed cautiously when operating saws for ventilation operations.
|(4) Hazardous DC voltage label on the combiner box.|
Use labels to identify all conduit and wire systems, junction boxes, conduit bodies, and other aspects of the solar PV system. Again, be aware that, although labeling is a requirement, labels may be loose, damaged, missing, or weathered.
When confronted with buildings featuring lightweight roof construction, keep firefighting personnel off the roof. “Big box” buildings may require the IC to think “outside the box” when tackling fires involving solar PV. Consider horizontal ventilation techniques using the large receiving door openings for ventilation and special call equipment as an aid (e.g., cranes, claws, lifts, and so on). In all cases, notify the IC immediately if ventilation operations are impeded.
- Scene lighting and exposure fires can provide a sufficient amount of illumination to solar modules to generate a “lock-on” hazard.
- Once compromised, a solar PV system may have inadvertent circuit paths.
- Damage to modules from tools may result in electrical and fire hazards. These anomalies may occur in parts of the system other than at the point of damage.
- Metal roofs may become energized.
- Panels have the potential to slide off at the roofline.
- Fires under the array but above the roof may breach roofing materials and decking, aiding in fire growth.
- Only use opaque tarps for blocking light sources from solar modules. [I do not recommend this because of the inability to maintain the tarp’s integrity and reliability (they are difficult to secure and are easily dislodged, especially by the wind) and the various sizes and configurations of the arrays.]
Salvage and Overhaul
During postfire operations, fireground personnel should never assume that any electrical components are safe to touch. Always exercise caution and treat the system as energized. Do not rely on “hot sticks.” They sense only AC voltage; they do not sense DC voltage.
|(5) Internal combiner box components.|
Additionally, a fire event may compromise the solar PV conduit and wire system, resulting in arcing, and may lead to a possible rekindle the next morning. Make sure to check the scene in the daylight after the event to ensure that no rekindle takes place. The system should not be reenergized until a qualified solar provider/electrical contractor can satisfactorily recommission the system.
Personal Protective Equipment (PPE)/Safety
Under normal circumstances, fire personnel should wear the appropriate PPE at a fire scene, but it is especially important to wear it during a solar PV fire. However, fire gloves and boots provide limited protection against electric shock. Also, solar modules become slippery when wet, so never stand on them. Additionally, toxic chemicals are a by-product of a burning solar module and are released during a fire. So, personnel must don PPE and have self-contained breathing apparatus as another option. Finally, the added weight of a solar PV array to the weight of the responders and their equipment may lead to a roof collapse if the structure’s integrity has been compromised.
Renewable energy systems such as solar PV are here to stay. As it was when the first hybrid electric cars hit the road, the fire service will need to adapt to manage incidents involving these systems. Adapting to this technology will require participation in continuing education and practical exercises because technology and code requirements are continually changing.
|(6) A centralized inverter.|
ICs and firefighting personnel will need to reinforce the aspect of isolation vs. disconnection. In preplanning for solar PV fire incidents, it must be stressed that a solar PV system is never totally disconnected.
The key to positive reinforcement is to stress to all first responders that, on arrival at a solar PV incident, the goal is to minimize and isolate the electrical hazard. Personnel should be able to differentiate between a safe zone and an electrified area. Once you identify these areas, you can conduct safe operations around the identified hazard.
As with any new firefighting challenge, knowledge and awareness of solar PV technology will replace fear of the unknown. In implementing this fireground strategy, you can effectively and safely mitigate an incident involving solar PV.
Callan, M. Responding to Utility Emergencies: A Street Smart Approach to Understanding and Handling Electrical and Utility Gas Emergencies. First Edition, Red Hat Publishing, 2004.
Grant, C. “Fire Fighter Safety and Emergency Response for Solar Power Systems,” NFPA, Fire Protection Research Foundation, Quincy, MA, May 2010.
Slaughter, R. “Fundamentals of Photovoltaics for the Fire Service.” Dragonfly Communications Network, Corning, CA, September 2006.
CAL Fire Office of the State Fire Marshal, “Fire Operations for Photovoltaic Emergencies.”
NFPA “Fire Fighter Safety and Emergency Response for Solar Power Systems-Final Report,” Quincy, MA, May 2010.
NFPA National Electrical Code (NEC) 2011, Quincy, MA.
NFPA National Electrical Code (NEC) 2014, Quincy, MA.
JOSEPH C. CAMAROTA, MIFireE, CFEI, IAAI, IABTI, is a 38-year fire service veteran and a former lieutenant with the Whitman Square Volunteer Fire Company No. 1 in Washington Township, New Jersey. He is a certified fire and explosion investigator and a member of the Institute of Fire Engineers, National Association of Fire and Explosion Investigators, International Association of Arson Investigators, and International Association of Bomb Technicians and Investigators. Camarota is also a certified fire official, a building and electrical inspector, a firefighter, and an instructor in the state of New Jersey. He has a bachelor of science degree in electrical engineering and an associate degree in science in architectural design. He is the electrical systems design director at Ray Angelini, Inc.
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