BY JOSEPH VISCUSO
What is a rooftop cellular base station? You have more than likely seen the cellular antennas attached to some rooftops in your district. You may have even seen the tall stand-alone cell towers in commercial areas. Although you see them every day everywhere you go, you probably never thought you would have to come in contact with them or that they might affect your decision making at a structure fire. Unfortunately, the minute you have to make the roof at a fire in a three- or four-story multiple dwelling to open the bulkhead door, you may have to deal with the antennas or other components of a base station. As the bucket of your tower ladder approaches the parapet, you start to wonder if it is dangerous. Can you place the ladder near it? Is it electrified? Could you use it to help gain access to the roof? This article will help you attain an increased awareness while operating in or around rooftop cellular base stations on two- or three-story multiple dwellings.
Today, you can find cell antennas on virtually any type of building and any type of occupancy in your district. The area you live in may be an indicator of the type of antenna setup you will encounter. For instance, in rural areas, you may see tall stand-alone towers with antennas on the top, called monopoles, in the countryside or on the side of a highway. In more densely populated areas, you may find them on rooftops of three- and four-story multiple dwellings in strategic areas. But, you may also find them on top of schools, hospitals, public buildings, water towers, church steeples, andbelieve it or notfire stations.
To keep up with the increased call volume of cellular phones, the cellular phone industry must increase the number of base stations. The cellular companies are identifying buildings that will provide wireless signal coverage to critical gaps in their service and leasing space on their rooftops. Unfortunately for the fire service, operating in and around base station equipment presents many hazards.
HOW DOES A CELLULAR BASE STATION WORK?
The cellular base station is an interface between a wireless cell phone and the hard-wired traditional telephones found in our homes. It allows two different types of phones to connect to each other. When you make a call on the cellular telephone, the cell phone uses radio waves to communicate with the cellular antennas found on rooftops or towers. The radio waves the cellular telephones use are in the microwave region of the electromagnetic spectrum. Once the antennas receive the radio signal, a transceiver converts it into digital signals. Traditional telephone lines then send the digital signal to a hard-wired telephone or another cellular base station, where the process is reversed and the new radio signal is sent to another cellular telephone.
For this process to function effectively, antennas must be placed in strategic locations throughout the area. The objective is to provide continuous coverage to cellular phone customers. To accomplish this, there must be a continuous interconnected series of antennas and cellular base stations that create a pattern similar to that of a honeycomb. As more and more phone customers drop their hard-line home phones and use cell phones as their primary phones, we will continue to see an increase in base station construction.
THE BASE STATION
The base station is comprised of the transmitting and receiving antennas, a radio room that houses all of the electronic equipment, a coaxial cable for connecting them, a power supply, and a backup power supply. Although all base stations have similar components, they are not all identical in their layouts.
Radio Room and Components
The radio room houses all the base station’s electrical components. This room may be found on the roof or in a more remote area of the building, such as the basement. It is not uncommon to have a fully functional shed-type structure or cabinet on the roof near the antennas. If this is the case, it most likely will be mounted on steel I-beams secured to the parapet. This preassembled roof-mounted cabinet resembles a large air-conditioning unit, and accessing this cabinet is dangerous and difficult. Most cabinets have a seven-point locking system for security reasons. Additionally, they are energized. Be careful when working around them with metal tools and water. If power in this structure is shut off and a small fire is present, you can extinguish the fire with a dry chemical extinguisher. If fire has already entered the cabinet or is threatening to do so, notify the cellular company immediately. The company may be able to remotely disconnect power to the unit.
Regardless of where this room is located, it must have its own 120- to 240-volt power supply, which may be split off the building’s main electrical panel or be independent of the building’s power supply. An independent power supply most likely will come into the building from a location remote from the building’s primary power supply. The radio room needs power to maintain large air-conditioning units in the utility room and to give power to the antenna’s electronic components. Identify all of the power supply shutoffs to the radio room and the building in general as soon as possible.
Within the radio room is an AC/DC rectifier system that converts the AC power supplied from the power company to DC power needed by the system’s electronic circuits. There will also be an uninterruptible power supply (UPS) system, which is essentially a battery backup system. The Federal Communications Commission (FCC) requires that a UPS system be available to provide at least a 12-hour backup for the cellular site, for public safety reasons. The radio room also contains a connection to the local telephone company’s lines (T-1 or E-1 lines), noise filters, amplifiers, coaxial cables, and alarm systems.
The UPS system resembles 12 or so car batteries connected together (photo 1). Be careful when operating around the batteries; they can fail and leak acid. The battery backup will allow the base station to continue operating if the power fails. It is also becoming common to have diesel- or natural-gas powered generators installed in case of prolonged power failures. The generators may be on the roof or in another remote area of the building. The incident commander (IC) must designate a company to locate the UPS and determine its type. Depending on your department’s staffing, you may have to call an additional company to the scene and assign it to locate the power supply, determine its type, and locate the shutoffs.
 (1) A typical battery backup found inside a radio room. (Photos by author.) |
Many times the radio room will be in a remote area of the building, such as in the basement or on an intermediate floor. Where space is available, the cellular companies retrofit an existing room to meet their specifications and store their equipment. Sometimes, they build walls and create a room in the basement (photo 2). Local building and zoning codes dictate the room’s construction features. For instance, some municipalities may call for a two-hour rating for the interior of the room; others may require a one-hour rating.
 (2) The new wall constructed in front of the windows in the basement of this three-story apartment building is a new radio room installation. |
If an alarm is transmitted from this room or another area of the building and the the ladder company must access the room, members should anticipate forcible entry problems. New doors are installed in these rooms to meet the required fire rating, usually a two-hour rating, and for added securityusually, a solid-core steel entrance door in a steel frame. If you encounter an inward swinging door, a rabbit tool should work. If the door opens outward, consider removing the hinges; otherwise, use an ax and a halligan.
The fire department should arrange with the cellular company the quickest and most efficient way to gain access to these rooms in an emergency. You may find a lock box that contains the keys and emergency contact information on the room’s exterior. If it is a nonemergency and department members are not familiar with the radio room components, it is best to wait for a representative of the cellular company to arrive before entering the room. When you do enter the room, treat all equipment as if it were energized.
If a smoke alarm is activated in this room, generally a central station will notify the local fire department. However, the signal may go directly to the cellular company, which will contact one of its service representatives and the local fire department. It is important that the fire department dispatch center have the proper emergency phone numbers should it be necessary to contact the cellular company.
Usually, a sign with the cell site’s FCC identification number and an emergency contact phone number [a Network Operations Center (NOC)] will be on or near the radio room’s main door. In case of an emergency, the IC can contact the cellular company using these numbers, and the cellular company may be able to remotely shut off the antennas, rectifiers, battery backup, and power supply. This will allow you to work in the area of the antenna; however, there will still be electrical power to the radio room’s main switch.
Preplan the NOC and FCC identification numbers so that your fire dispatcher has the numbers before an emergency arises. If the fire is near or in a radio room, the numbers on the door could be destroyed, which could cause a delay in notifying the cellular company.
Suppression System
Depending on the municipality’s codes, the radio room may have an independent suppression and detection system. The suppression system could be anything from a fire extinguisher to a more expensive clean-agent system. Because of the high cost of the equipment in the radio room, cellular companies are installing clean-agent systems. These systems are ideally suited for protecting sensitive electronics, because they are electrically nonconductive. If a site was constructed before 1998, it is possible that a halon system may still be in use. On March 5, 1998, the U.S. Environmental Protection Agency (EPA) issued a final rule covering the sale of halon blends and the handling and disposal of halon and halon-containing equipment. Although a contractor cannot install a new halon system, if an already existing system is discharged, it can be recharged with reclaimed halon. If a halon system is deployed, do not enter the area without being on air. Because of toxic gases (including the decomposition products of the halon itself) and potentially lower oxygen levels, thoroughly ventilate to clear the room of these toxic materials and to restore normal oxygen concentrations. Multimeters are ideal for monitoring the percentage of oxygen in the room.
The FM-200® Waterless Fire Systems Work is one of the clean-agent systems in use. It does not remove the oxygen from the atmosphere in the room but removes heat energy from the fire. This system can extinguish a fire with only a seven percent mixture with air. This quick-acting system gives a warning prior to deployment and has proven to be safe even if it deploys while a worker is in the radio room. If on arrival this system is in the process of being deployed or has already been deployed, the IC should ensure that the air-circulating system remains in operation so the unit’s fan can circulate the FM-200®. This action is advised only when it will not cause the fire to spread and will fully disperse the clean agent.
When operating in a radio room with smoke, you must wear full personal protective equipment and SCBA and use monitoring equipment to check the atmosphere. Newer radio rooms may be equipped with ventilation systems that are hooked up to the suppression system. Although not common, you may find a radio room set up in a room that has a sprinkler system installed (photo 3). If this is the case, the cellular companies most likely will change the sprinkler heads with a higher temperature head. Preplanning is essential for fully understanding the suppression systems within these rooms.
 (3) This large storage closet was turned into a radio room. The sprinkler system existed prior to this installation. |
If the power to the room needs to be cut, be sure to assign a member to confirm that the power supply to that base station radio room is actually cut. Also, remember that there is a battery backup that must be disconnected. Notify the cellular company of any actions you take; the IC must get the estimated time of arrival of a serviceman.
One type of fire you may encounter in a radio room is one caused by an electrical malfunction that causes a spark to ignite a combustible component. If no suppression system is installed, shut off the power supply and use a Class C fire extinguishing agent. Simply turning off the A/C power may not extinguish the fire. First, locate the main breaker for the A/C power supply in the room and shut it down. Then shut the breaker for the UPS system. Use a minimum of water in this room, because of the high cost of the equipment and the electrical dangers. However, if the building’s structural components are involved, you may have to put hoselines into action. If you encounter fire in a radio room, send members to other parts of the building to check for extension immediately. Check the coaxial cable runs first.
Coaxial Cable
This coaxial cable is similar to the average television or computer coaxial cable, but it is substantially larger. The standard coaxial cable is approximately 15⁄8 inches in diameter. The cable allows the radio frequency (RFelectromagnetic energy such as radio waves and microwaves) signal to travel from the radio room equipment to the antennas. It may look intimidating, but only a small amount of electricity is running through it, usually three to four watts. The cable has a thin black polyethylene outer jacket that covers a corrugated copper conductor. A foam dielectric and an inner corrugated copper conductor are inside (photo 4). Some cables have a fire retardant jacket; however, if they are not required by building codes, the cellular companies may not voluntarily install them. If the cable’s outer jacket is not fire retardant, fire could run along the exterior of the cable. There are documented cases where the cables caught fire and burned within the interior of a monopole antenna.
The cables are easily identifiable and traceable and will usually exit the utility room through a port plate (photo 5). There is a rubber boot around the cable, where it passes through the port plate. This boot is for weatherproofing only and affords no fire-stopping. Once the coaxial exits the radio room, it travels to the antennas. The number of cables is determined by the number of antennas (usually 10 to 16 are present). If the radio room is on the roof, the cable will be readily traceable from the room, through the cable trays to the antennas. If the radio room is in the basement or a remote area of the building, the cables may be visible, traveling to the antennas along walls and ceilings up through vertical shafts or cable trays and onto the roof, where they travel through cable trays to the antennas. If fire starts in the basement outside of the radio room, check the radio room for extension along with any shafts or voids in which the cables run. When searching for fire extension, check first the area where the coaxial cable exits the radio room.
 (5) This coaxial port plate was installed in an old window before any coaxial cables ran through it. |
When operating around the coaxial cable, never cut through the cable. The RF traveling through the cable is concentrated in a small area; if the cut end were to come in contact with a body part, it could cause burns.
Cable Trays
Cable trays are used to protect cables on the exterior of the building. They are usually aluminum or lightweight metal and resemble aluminum ladders that are lying flat on the roof or attached to the side of the building (photo 6). Cable trays are not secured to the roof, because cellular companies try not to penetrate the roof in an effort to minimize damage and leaks. For this reason, the trays lie on the roof and are held in place by gravity. To keep the trays off the roof, they may be attached to small pieces of four-inch by four-inch lumber or hollow PVC posts, creating a greater tripping hazard for firefighters working on the roof (photo 7). The coaxial cable is secured to the cable tray with zip ties, which are wrapped around the coaxial and the cable tray rungs. A metal cover plate is placed over the top of the tray and secured to the side rails with screws.
 (7) Cable trays running along the backside of a parapet. The top is not yet installed. As you can see, they are sitting on 4 × 4s. |
The cable tray and all other components of the base station are grounded to prevent electrical shock and protect from lightning strikes. There is no power to the cables or cable trays; however, if any part of the cable tray contacts an exposed power line, it may become energized. Take safety precautions.
Under fire conditions, smoke will obscure the cable trays and increase the tripping hazards on the roof. If working on the roof near the parapet, watch for cable trays running along the rooftop on the back side of the parapet. You can easily trip over the tray or slip on its cover, especially under wet conditions. Sometimes, it may be necessary to ventilate the cockloft area by cutting a vent hole in the roof. The roof team must keep the location of the cable tray in mind when planning to make a vent hole. If fire should impinge on the cable tray, the coaxial cable could become involved. The fire will run the length of the tray. If a cable tray is running up the exterior of the building, it likely will be in the rear of the building or in a light and air shaft (photo 8).
Vertical Shafts
As stated earlier, the cellular industry makes every effort to avoid penetrating the roof when installing stations. If the cable trays cannot be installed on the exterior walls of older multiple dwellings, contractors may use the abandoned dumbwaiter shaft or garbage/compactor chute to run the cables. One way to quickly determine if a shaft is being used for coaxial cable is to have the roof crew advise where the cables for the antennas are entering the roof. If the cable can be seen traveling over the side of the building’s parapet in cable trays, your problems may be limited to this single avenue of travel. The roof crew must still inspect all other vertical shafts; it is not uncommon to have coaxial cables running up both the side of the building and a dumbwaiter shaft. A simple way to tell if one of these dumbwaiter shafts is in use is to look for a port plate cut into the side of the shaft in the area where it extends above the roof (photo 9). The coaxial cable will exit from this port plate into the cable trays, eventually ending at the antennas. The IC must ensure that the interior of this shaft is inspected for fire spread. If fire has entered this shaft, the roof division must vent the top of this shaft, being careful not to damage any cable lines. Check all floors for fire extension, and place hoselines in position at the location where the shaft passes through the floor.
 (9) This old dumbwaiter shaft is used as a conduit to house the coaxial cables in this four-story building of ordinary construction. No fire-stopping was used. |
The lack of fire-stopping is a concern when shafts are used to house coaxial cable. Photos 10 and 11 show the difference between proper and improper fire-stopping. Photo 12 depicts an old dumbwaiter shaft used as a conduit to house the coaxial cables in a four-story building of ordinary construction where no fire-stopping is present. If a fire were in the basement radio room and it was not detected early, it could run along the cables and travel up to the roof. Remember, these shafts may not have been used for many years and the bricks and mortar may have deteriorated. In addition, contractors may have used these shafts to run phone, electric, and plumbing lines. Running these lines to each floor compromises the structural component.
 (10) Improper fire-stopping of the coaxial cables. |
 (11) Proper fire-stopping of the coaxial cables. |
 (12) This shaft has no fire-stopping from the basement to the roof. The rubber boots around the cables running through the port plate are for weatherproofing only. |
The forcible entry challenges the dumbwaiter poses raise another concern. When these shafts are abandoned, it is not uncommon for the owners to nail shut the access doors originally installed on each floor. You must locate and open these doors in case you need access. Inspect and check the doors on all floors for fire extension when a fire is present.
ANTENNAS
Sector or flat-panel antennas typically are found in rooftop installations in urban areas. Sector antennas are rectangular panels about one foot wide by four feet high (photo 13). This type of antenna is usually arranged in groups of three; however, the number could vary. Traditionally, one antenna is used for transmitting; the other two are used to receive signals. You might also find single antennas that both transmit and receive. When transmitting, the radio signal of this antenna resembles a pie shape with the point of the pie facing the antenna. As the distance from the antenna increases, the shape widens. Always assume that all antennas are transmitting.
 (13) Sector or flat-panel antennas typically are found on rooftop installations in urban areas. These rectangular panels are usually arranged in groups of three, but the number can vary. |
There are many ways to secure a sector antenna to a building. In older structures, masts may be attached to the parapet’s facade with U-clamps and bolts. This type of arrangement creates an eccentric load on the parapet. If fire impinges on the connections, the mast could fall from the building. Photo 14 shows a typical mast setup. Never use these poles or antennas as a handhold when on a roof. The U-clamps or poles could fail and the pole could pull away from the building, causing you to fall or slip. These clamps may be attached on the front or back side of the parapet.
A ballast roof mount or a sled mount may also secure these antennas. Ballast mounts are nonpenetrating; they secure cellular antennas to the rooftop. Essentially, they are steel structures placed on the roof and held in place with concrete blocks and gravity (photo 15). This allows the cellular company to move the antennas easily when necessary for better reception or roof repair. A ballast roof mount system creates a concentrated load on the roof; this is a load that is applied to a small area of the roof. If the roof structure below the ballast mount is under attack by fire, the weight of the ballast mount may cause premature collapse. A roof team encountering a ballast roof mount in a top-floor or cockloft fire should notify the IC and all members within the building. If fire is under a ballast mount, the IC may have to consider withdrawing the interior attack teams and switching to an exterior attack earlier than anticipated.
STEALTH BASE STATIONS
Aesthetic concerns have led the wireless telecommunications industry to disguise rooftop base stations by using stealth base stations (SBS). The SBS towers or antennas are less apparent to the casual onlooker. They could be an antenna constructed as a cross on a church steeple or a more complex false parapet type of construction. The building in photo 16 shows what appears to be a high parapet on the front corners of a three-story apartment building. However, these parapets are new and made of fiberglass panels painted to resemble the original building’s characteristics. A closer inspection of the sides reveals the presence of a three-sided fiberglass panel box (photo 17). The fiberglass allows radio waves to transmit through it without any notable loss of power.
The new SBS pose additional concerns for firefighters. Photo 18 shows the steel structure supporting the cellular antennas and false parapets. The steel I-beams are resting on the top of the parapets on the front and side of the building spanning the corner. This is also a concentrated load that was not designed into the original building plans. If fire impinges on the unexposed steel I-beams, they will expand and push out the front and side parapets, causing an outward collapse on two sides of the building (photo 19). The roof team must immediately notify the IC of this situation so that he can establish collapse zones on multiple sides of the structure. Additionally, if fire is venting out of the roof in the vicinity of the I-beam, it would be beneficial to apply a protective stream to this beam to cool it and prevent any expansion. Do this from a safe area such as a tower ladder or the roof of an exposure. If you need to vent the roof, be careful to prevent fire impingement on any of the cellular base station equipment. Try to arrange the cuts with the maximum distance between the vent hole and the equipment related to the base station.
 (19) This close-up of the steel support I-beam resting on the parapet shows that the I-beam is secured to the parapet with lag bolts and has a waterproof membrane to protect it from the weather. |
In a traditional base station, antennas are attached to the parapet’s exterior façade. This makes them easy to identify, and you cannot walk in front of them. With these newer stealth installations, the antennas are hidden from view. You may not even know they are there, and antennas could even be hidden in the center of the roof. In Photo 20, firefighters operating on the roof will be exposed to RF without even knowing that an antenna is present.
ROOF OPERATIONS
When gaining access to the roof, never use an approach that will necessitate walking in front of an antenna. You will not be able to determine if the antenna is transmitting or how powerful it is. Sometimes, it is difficult to determine the direction in which the antenna is pointing. Treat every antenna as if it were a live transmitting antenna. A good rule of thumb is to maintain a 10-foot distance between you and the antenna. The presence of antennas limits the access points to the roof; keep in mind that you may have to use another means of egress. A member of the roof team should do a 360 of the roof to try to determine the locations of the antennas and the point at which the power supply is coming into the building. Many times, the power for the base station is coming in from the rear of the building. This information should be transmitted to the IC.
IDENTIFICATION
Normally, you can readily identify older rooftop cellular base stations from the exterior by viewing their antennas on arrival. However, newer stealth towers may be visible only from the roof or preplans. When on the roof, firefighters must perform a recon for the IC that includes looking for antennas attached to parapets or on ballast mounts or stealth panels that conceal the antennas from the street level. If antennas are not visible from street level, then placards such as those described in National Fire Protection Association (NFPA) 704, Standard System for the Identification of the Hazards of Materials for Emergency Response, for identifying hazards or RF warning signs may be the only indication that a base station is present. Normally, (as noted) the only RF sign on a multiple dwelling would be on the interior of the bulkhead door leading to the roof. This sign warns occupants of the danger so they do not walk on the roof with the antennas (photo 21).
As stated earlier, there should be a sign near the door to the radio room citing the FCC ID number and the NOC emergency phone number. Currently, there are no standards applicable to placing signage on the exterior of a building to warn firefighters of the presence of a cellular base station. As the fire service lobbied to have signs placed on the exterior of buildings warning of the presence of a truss roof or truss floor, we should lobby to have RF placards installed on the exterior of buildings to warn of the presence of antennas (photo 22).
RADIO FREQUENCY DANGERS
The danger to firefighters operating in front of an antenna is the presence of RF. The FCC says, “In order to be exposed to levels at or near the FCC limits for cellular or PCS frequencies an individual would essentially have to remain in the transmitting beam (at the height of the antenna) and within a few feet from the antenna.” This is not a concern for the firefighters at the street level; however, it is a major concern for firefighters who have to gain access to the roof using an aerial ladder or a ground ladder. If an antenna is present, make every effort to access the roof from another, safer area. If you can gain access only through close proximity to an antenna, do not go within 10 feet in front of a directional panel antenna. Maintain a three-foot distance from the sides and back. If you cannot distinguish the front from the back, access the roof from a different location if you cannot establish a 10-foot minimum distance.
If under extreme circumstances you should have to approach the front surface of an antenna, be as quick as possible to avoid more than a few seconds of exposure to RF. Standard structural firefighting turnouts do not protect against RF. Never touch an antenna; you can get RF burns. Always use time, distance, and shielding when working in and around antennas.
Use solid structures such as a bulkhead door and parapets on exposure buildings as shielding. Although the aluminum around the bucket of a tower ladder may shield you from some of the RF, it could reflect the RF back at members working on the roof. While working in the bucket of a tower ladder, truck company personnel should also look for antennas on the rooftops of the exposure buildings. Concentrating only on the fire building may prevent you from noticing antennas on the parapet behind you and subject you to RF.
Another health issue related to RF is thermal effect, tissue damage that may occur during exposure to RF. This is the result of the body’s inability to cope with or dissipate the excessive heat generated. This is similar to placing your hand in a microwave while it is operating. Two areas of the body are particularly vulnerable to heating from RF, the eyes and the testes. Both are vulnerable because of the lack of available blood flow to dissipate the excessive heat load. Shocks and burns could be other effects of RF exposure.
Additionally, body heating, confusion, vertigo, headache, blurred vision, a bad or metallic taste in the mouth, and nauseousness are some other symptoms that would indicate an overexposure to RF. If you experience any of these symptoms, notify the IC immediately and move away from the vicinity of the antennas.1 (Health effects are discussed in more detail in the FCC Office of Engineering & Technology, Bulletin 56, fourth edition.)
PREPLANNING
Many times, the only way to know that a rooftop cellular base station is present is through preplanning or conducting an in-service inspection of the building. Company officers should ensure that all members are made aware of the presence of antennas and that the information is entered into the department’s computer system along with the NOC emergency contact numbers, the building’s address, cell site FCC ID numbers, the locations of radio rooms within the building, the primary and backup power supplies, the voids used for coaxial cable, and the accessibility to the base station’s components. Additionally, contact the cellular company to see what its time of arrival would be in an emergency and if it can remotely shut down the power in the base station and its components.
Be proactive in identifying the presence of these rooftop base stations, and become familiar with their dangers. Although we may have only limited contact with areas containing antennas, that contact most likely will be during an emergency. Preplanning will enable us to identify the areas of concern in advance and create a standard operating procedure to limit the dangers in an emergency. Your department should become involved with the planning review process and have input in your municipality’s decisions related to selecting locations for rooftop cellular base stations. The technology in the cellular industry is changing daily, bringing new dangers for us. Always be aware of your surroundings; never become complacent.
endnote
1. “ RF Radiation Awareness Communications Bulletin,” Bechtel Communications, Inc., 2007.
JOSEPH VISCUSO is an 18-year veteran of the fire service and deputy chief in the Kearny (NJ) Fire Department. He is a member of the New Jersey Deputy Fire Chiefs Association and a level 2 fire service instructor.
