Changing High-Rise Fireground Tactics - The Dangers of Redundant Power Supplies

Aug. 1, 2005
Curtis S.D. Massey reviews the dangers of redundant power supplies including tenant UPS systems in part one of this series.

The following two fire summaries are based on official National Fire Protection Association (NFPA) investigative reports:

Hinsdale, IL, May 8, 1988 - A fire breaks out in a telephone exchange building. According to the NFPA investigative report, there was a 40-minute delay from the time the alarm was transmitted to the time the alarm was delivered to the local fire department, mostly due to the fire affecting the telephone lines and human error. Damage was estimated at $40 million to $60 million. The fire, involving telephone cables in a suspended ceiling tray and electrical components, produced thick, black, heavy "cold" smoke that banked down to near floor level, hindering searches and suppression efforts. Hot, molten material (probably steel, copper and plastic) rained down on firefighters attacking the fire. Large arcing was also occurring with the energized equipment, spitting hot debris on the attack crews. It took over two hours and multiple attempts to remove all power to the fire area, due to redundant sources and no simple means of emergency shutdown. Six and one-half hours after arrival, the fire was declared officially out. Firefighters were subjected to great risk in successfully controlling this serious fire, which impacted telephone service on a national basis for some firms, as well as local 911 service. Los Angeles, March 15, 1994 - A fire breaks out in a telephone exchange building downtown, involving batteries and power distribution units for the telephone equipment power plants. After a delayed alarm notification to the Los Angeles Fire Department, fire personnel responded and successfully controlled the fire in short order. Numerous batteries were damaged or destroyed during the event. An estimated 30 gallons of acid was released onto the floor of the fire area, spreading out 20 feet beyond the area of origin. This spill was not immediately recognized by fire crews due to low visibility, but mostly avoided. Despite the acid spill, arcing of energized equipment and a heavy, dense, "cold" smoke condition hindering their operations, no firefighters or civilians were lost or seriously injured. However, local telephone service was affected, including 911.

The focus of concern from these two NFPA reports is evident. Reviewing the full reports, the similarities between the two events are: delayed alarms, difficulty in locating the seat of the fire, dense/heavy, "cold" smoke, arcing/shorting electrical equipment, difficulty in ventilation, firefighters forced to attack the fires without power disconnection to involved area.

What bearing do these two telephone building fires have on high-rise buildings? With new-age technology constantly evolving, office high-rises are experiencing more and more changes that can affect firefighter safety. One area that seems to escape notice is the rapid growth of backup power supplies on any given floor of a commercial or government building.

Is your department prepared to wait 30-45 minutes before stretching the first hoseline on a working fire in a high-rise? Even under ideal circumstances, it can easily take that long to de-energize power to a tenant who possesses a redundant power supply. These systems are now becoming the norm, no longer the exception, with tenants such as law firms, banking firms, accounting firms, trading firms, data storage or processing outfits and telecommunications companies (hence the tie-in with the noted fire reports). To state this issue in the simplest of terms: These businesses do not want to lose power to their mission-critical systems for anything shy of a nuclear strike!

What is a UPS system? A UPS (uninterruptible power supply) is a device used to convert a stored energy source into electricity to feed critical equipment in the event of a power disruption. Although some UPS manufacturers are beginning to use alternative sources such as flywheels or even compressed inert gases, by far the most common stored energy source is in the form of batteries. Ordinarily, a number of batteries are connected together, referred to as a "bank" or "string" of batteries, to provide a specific amount of operating time in the absence of an input power source. This time can vary from 10 minutes to an hour or more (most central office telecom buildings have at least eight hours). Multiple strings can also be connected together to provide even longer operating times.

There are numerous types of batteries, but most UPS manufacturers provide lead-acid batteries that are vented or sealed. Sealed batteries, usually referred to as "maintenance-free" (i.e., gel cell or absorbed glass mat), weigh from two to 80 pounds each and normally are found in smaller commercial applications, usually housed inside cabinets. These are commonly referred to within the industry as VRLA (valve regulated lead acid) batteries (see photo 2). The vented type (i.e., flooded or "wet cell", the most common reference) are typically found in larger applications, such as telecommunications and data centers, weighing 350 to 400 pounds each and mounted on open racks. Both types generate hydrogen gas. Although the vented batteries are designed to normally release it into the open air, sealed batteries release hydrogen gas as well, especially during the "break-in" and overcharging/equalization phases.

Wet-cell battery hazards involve the existence of sulfuric acid in an electrolyte solution and the production and release of hydrogen and oxygen during charging, including "float" or maintenance charging. The dangers of highly corrosive sulfuric acid are obvious. However, firefighters must be aware of the flammable/explosive nature of hydrogen gas when entering these tenant spaces. Small amounts of hydrogen gas normally are released during the charging cycle of wet-cell batteries. Larger volumes are produced when battery overcharging occurs or high-temperature conditions exist, especially with wet-cell types.

Sealed batteries, the most common type you will encounter, are usually constructed with its electrolyte held in a sponge-like material inside the container. If the case is ruptured, no acid is likely to spill out. Because of the chemical reactions which occur in the battery, nearly every "sealed" UPS battery has a safety valve to vent internal gases if the internal pressure becomes too great. Theoretically, this should never happen if they are maintained properly and do not malfunction internally, although again, they do release some hydrogen gas, especially during break-in.

A common misconception is that these batteries are completely "maintenance free," as they are frequently called. The phrase "maintenance free" refers only to the fact that internal electrolyte solution levels are not to be adjusted over their usable life (think of most of today's car batteries versus those of years ago, when you had to add water to them periodically). Since these batteries are usually housed inside a closed cabinet (sometimes even closets), their condition is not readily apparent to the equipment owners ("out of sight, out of mind"). If the batteries are not regularly maintained, they can corrode, develop cracks and ruptures, or degrade until becoming entirely unusable. They are especially vulnerable to heat damage.

Over time, the hazards of these batteries can become greater without proper maintenance. As a result, risks such as the release of hydrogen gas, although less likely, can still be possible with these types. It has been expressed to the author by chief engineers interviewed that most sealed battery UPS owners have little, if any concept, of the associated dangers with their batteries: "Wet-cell batteries are relatively abuse forgiving, while VRLA batteries are relatively abuse unforgiving. Hydrogen gas from either type of battery may be released and accumulate to explosive levels" ("Lead Acid Battery Hazards" by Robert "Bob" Taylor, president, Morning Star Industries Inc.).

Upon being advised of a fire involving a tenant space with batteries (especially wet cell), it should be determined whether the room is ventilated before leaving the lobby, due to the possible threat of a hydrogen gas buildup. The results of carelessly entering this area if a gas pocket exists and finds an ignition source at the same time as entry may prove catastrophic (see photo 1). The roof of this tenant space was blown off and interior walls were heavily damaged. One must consider how this may play out on an upper floor of a high-rise and its effects on the structural integrity of the building. At the very least, glass will be blown out and onto the street below, endangering both civilians and first responders, as well as the release of acid mist.

It is common for stand-alone data/banking/trading centers and telecommunications buildings to have dedicated hydrogen gas detection devices and automatic purge ventilation systems and/or constant ventilation for the battery rooms. These tenants occupying space in a high-rise building are far less likely to have purge ventilation capability if they moved in after design and construction. Codes, although relatively ambiguous, should address this, but they are not always followed or enforced. Also note that vent fans may not be serviced and maintained. This presents a high-level of risk to firefighters if there is no method of removing a build-up of flammable gas before entering the danger area where the leak or fire is occurring: "The electrochemical energy of a fully charged battery is substantial enough to vaporize or evaporate over half the battery materials. This one fact alone should sensitize us that the dangers of a battery are much more than sulfuric acid being stored in a container" ("Lead Acid Battery Hazards"). Caution should always be exercised.

What happens when a fully charged lead-acid battery cell is shorted?

Hopefully, the device shorting the battery becomes hot and melts or vaporizes and clears the short. In large installations, there is enough energy available to vaporize copper buss bars and other circuitry. Vaporizing copper has the same expansion rate as exploding dynamite.

If a shorted battery cell does not clear the external short, the electrical connection between the battery terminals allows for a very rapid chemical reaction as the sulfuric acid converts the lead and lead dioxide to lead sulfate. Now the electrical energy is not dissipated externally, but internally in the form of heat. The resulting temperature rise inside the battery cell literally destroys the cell and actually may vaporize the battery materials including the electrolyte and lead.

Actual battery applications are comprised of multiple battery cells. A typical car battery has six cells in series. Telecommunications typically have battery strings of 12 and 24 cells each. Industrial Supervisory Control and Data Acquisition (SCADA) systems typically have 60 cells in series. UPSs over 10 KVA typically have 240 cells with a string voltage of 545 volts DC! When a short is placed across a string of batteries, the resulting fault current will begin discharging all of the cells until one or more cells fail. Now, instead of each cell destroying itself, the cells that have not failed dissipate their energy into the failed cells. Not only do the failed cells typically melt and give off vapors, but these failed cells often become arc furnaces due to the energy contribution from the rest of the battery string. The amount of energy dissipated in the failed cell(s) is usually enough to totally vaporize the whole battery unless the battery fails in such a way as to disconnect the circuit. When the battery cell is on a grounded rack or mounting surface, the circuit continuity is continued through the battery cell's melted parts and the conductive mounting surface. This type of destruction of the battery cell(s) is typically what is called a battery fire. Substantial clouds of acid mist and vapor will be present during this type of fire and will expectedly overwhelm a ventilation system ("Lead Acid Battery Hazards").

What is a lead-acid battery and how does it work?

Lead-acid batteries are, in a way, a chemical miracle. The active materials are simply lead and sulfuric acid and lead compounds formed through the charging and discharging of the battery. When a battery is charged, additional energy is "stored" in chemistry changes. When a battery is discharged, energy is "removed" through the reversal of these chemistry changes. When the battery is fully charged, the positive plate is lead and the negative plate is lead dioxide. The sulfuric acid is the strongest when the battery is fully charged and may be as high as 40% pure sulfuric acid mixed with 60% water. Sulfuric acid is classified as an Extremely Hazardous Substance (EHS) and lead, lead dioxide and lead sulfate are classified as Hazardous Materials ("Lead Acid Battery Hazards").

It is important to note that the tenant may or may not have designed and installed a proper spill containment envelope. There are good (see photo 2) and bad ones, where companies deem egress aisle ways or the entire room as their "spill containment area". This, of course, is the same area where firefighters entering this room will be walking and possibly crawling, through pools of sulfuric acid.

The hazards of battery acid include (excerpted from the Morning Star Industries Inc. report):

  • Water reactive
  • Bulk neutralizer reactive
  • May cause organic absorbents to ignite
  • Dissolves and crumbles cement
  • Flows like water
  • Decomposition may include acid fumes, sulfur dioxide, sulfur trioxide, hydrogen and arsine gas
  • Neutralized battery acid may contain lead, lead sulfate, lead dioxide, arsenic and antimony

Risks of Increased Floor Loads

Regardless of the type of UPS batteries in large applications, they all present a concentrated load that the structural floor assembly may or may not be designed to handle (especially heavier wet-cell type). In some cases, the floor may have to be reinforced or the load demand distributed by way of transferring the weight between columns (see photo 3). There are high-rise buildings where battery banks have been added to office floors that were clearly not designed to handle the additional load, exceeding engineering specifications. Such a floor may be stressed to near its failure point. A severe fire on the floor below may cause this floor to fail, possibly resulting in a progressive "pancake" collapse all the way down to the basement.

Extremely heavy battery banks, package air conditioner units, computers and other equipment are being placed on floors that were designed for office furniture and people. This threat must be considered in a fire chief's tactical decisions and included in pre-fire plans. "A car battery that weighs 30 pounds will contain about one gallon of electrolyte. For 1,000 gallons of electrolyte, there will be 20,000 pounds of lead and lead compounds. A large data center or telephone central office may contain over 10,000 gallons of sulfuric acid. If this same sulfuric acid were stored in 55-gallon drums, that would equate to nearly 200 drums. Morning Star Industries estimates there is well over 20 million gallons of battery acid in non-industrial classified business use facilities in the United States. Sulfuric acid is the most widely used industrial chemical in the nation" ("Lead Acid Battery Hazards").

Why do businesses require redundant power supplies? Some tenants have battery backup as an alternative source of power in the event of loss of primary electricity to their networks. Others (the majority) use the UPS as the primary source for their critical equipment, since it provides a steady flow of energy at all times while utility power is constantly maintaining the batteries in a charged state. Plus, when it is run through their power converter, the electricity is "cleaned up." This type of UPS is called an "online", or "double conversion" system.

Power spikes or surges, pauses, brownouts, etc., can be very damaging to sensitive and expensive equipment. So, the electricity coming into the tenant space (AC, or alternating current) goes through a DC rectifier (see photo 4) and is converted over to DC (direct current) power, paralleling the battery units by way of a UPS module, then converted back to AC power by an inverter, then sent through a delivery mechanism called a PDU (power distribution unit) and on to the tenant's business equipment. The power can be up to 99.999% pure, or clean, power versus utility company power, which is considered "dirty," or impure. The batteries may be adjacent to the equipment they serve, in their own room nearby or on another floor of the building. These batteries must be isolated when a fire involves the noted equipment they feed. The shutoffs are typically found in the vicinity of the batteries or at the UPS. Remember, though, even when batteries are isolated, they are capable of generating electricity and present a serious shock hazard, so due caution must be exercised when operating near them at all times.

The most common methods of providing electricity to a tenant's equipment can be from multiple sources, such as:

  1. Primary feed from the utility company off the main grid coming into the building.
  2. Secondary feed from another electrical grid on an adjacent street.
  3. Battery backup (UPS) system.
  4. Emergency generators.

The primary and secondary power feeds from the utility company normally come in through the basement or first floor, but not always (see photo 5). These independent feeds may run in tandem to feed a tenant's electricity demands, so if one grid goes down, power continues to flow. There may also be a different application where one grid's feed simply backs up another and is constantly in a sort of "stand-by mode."

As the electricity enters the building, it is sent to the transformer vault, where the voltage is stepped down/reduced to a manageable voltage. It is then sent to the switchgear rooms, where it is separated into different feeds for all the demands within the building. Then it goes up to all the tenants through a riser (or risers) in the core. In taller buildings, you can expect to find other transformer vaults on upper-level mechanical decks and/or smaller vaults on tenant floors (usually every three to five floors). The meter bases and main breaker panels can usually be found in the vicinity of the transformer and switchgear rooms, with individual breaker panels on each tenant floor. However, many other configurations may exist. Most high-rise buildings have one, two or more electrical closets on each floor that provide some or all of the power for the floor. Caution should be advised as some computer rooms and critical equipment on a floor may very well have dedicated riser feeds from building switchboards and emergency generator sets providing multiple sources of disconnect, sometimes from both the top and bottom of the building at the same time.

EPO Switches

Some tenant areas possessing computers or telecommunications equipment have EPO (Emergency Power Off) switches mounted on the wall near the exit/entrance to the space, usually behind a plastic housing (see photo 6). Codes governing these devices and their enforcement are not dissimilar to the previously mentioned battery room issues. This device may shut off any and all power to that space, lighting, air conditioning and the computer equipment itself. Sometimes in mission-critical applications, it just shuts off power to the lighting and air conditioning, leaving the computers or telecom equipment energized. It may not isolate the backup power supplies (batteries and generators). In other words, don't trust it until it can be absolutely verified that ALL power has been shut down in the fire area.

The EPO function may isolate power outside the room for optimum safety, but it will most often simply act as a local "kill switch" to the main electrical components and distribution panels (PDUs). This means that there is still live power coming into the room and present at the inputs to that equipment! Do not trust that the "Emergency Power Off" label is accurate! Some tenants have EPO switches that shut off all power to an area, but when new equipment is added during expansions, it is not tied in to the existing EPO switch. Again, do not trust until verified and remember that this switch will likely be in the potential fire area. Stretching a hoseline into this room and flowing water could result in serious injury, or worse.

Some equipment fed by these backup power supplies can be very high voltage. The high-voltage cabling in the tenant area may be under raised floors, in concealed ceiling void spaces or in exposed ceiling grids. Expect there to be a dense smoke condition with very limited visibility. The smoke will likely be "cold" and heavy, banking down to floor level. NOTE that data center UPS systems may have a "shunt trip" circuit breaker in the battery cabinet. Tripping this breaker with the EPO may result in an electrical arc that ignites the hydrogen gas that may be in the cabinet!

Emergency Generators

This item will be covered more thoroughly in Part 2 of this article. When utility power is lost, the tenant's batteries handle the full load demand until their generator(s) start and come up to speed with a pre-designated warm-up time. The unit(s) then provide all necessary power until electricity is restored or fuel supplies are exhausted (or interrupted). There are diesel- and natural gas-driven generators. With a fire involving equipment serviced by emergency generators, they must be shut down to reduce risk to firefighters operating in the tenant space. The cut-offs can often be found in the immediate vicinity of the unit(s).

Fire Protection Systems

The space housing tenant equipment/computers may be protected by a variety of special suppression systems (such as Halon, FM200 or other gaseous agents) and/or standard "wet" sprinklers, water mist systems or a dry-pipe pre-action sprinkler system. There also may be no protection at all. If Halon has discharged, self-contained breathing apparatus (SCBA) must be donned prior to entering the space involved, due to the low oxygen content level of the atmosphere.

If a gaseous suppression flooding system exists, the space may have dedicated purge ventilation capability for gas removal. The manual activation button is usually located in or near the computer equipment area, usually at the entrance/exit point. With a dry-pipe pre-action system, the sprinkler piping is flooded with water when the alarm activates, yet nothing comes out of the heads until they actually release.

If a gas agent system is present, this system has usually activated by now, providing a "first-line defense" before the more damaging sprinkler water is utilized. This proprietary sprinkler system has its own control valve that must be shut off when the fire is determined to be under control. This valve may be anywhere, including in the tenant space itself. It may be in a closet or even above the ceiling. Rarely is it found in the stairwells, where firefighters would expect it to be. How many firefighters would think to look in these hiding places for sprinkler shutoffs? When entry is made into this tenant space, you will most likely not be aware that an independent sprinkler system is operating. Without a pre-plan or the guidance of a knowledgeable building engineer, fire crews would probably isolate the building's wet system valve(s) (if they are located in the stairwells) once the fire is under control and then after a period of time has passed, drain the risers from either the basement or the nearest OS&Y valve. This would obviously result in considerable damage to the tenant's contents and probably floors below.

Important note: There may also be a possibility of having energized water on the fire floor from the discharging sprinklers hitting equipment that may not de-energize. For optimal safety, all power should be shut off to the fire area before entering the space to finalize extinguishment and to isolate the dry-pipe valve. Firefighter safety should always be a first consideration. If entry is attempted without power disconnection, extreme caution should be exercised.

High-Security Access

Most sensitive computer rooms housing valuable equipment/data have touch-pad or card-key entry systems. To avoid unnecessary forcible entry if these systems are not tied-in to the building fire alarm system (which is typical), request assistance from on-site tenant IT (information technology) specialists, if available, during normal business hours and it is safe for them to approach the room entrance. After-hours access may require waiting for technicians to respond or making forcible entry, if a sense of urgency is dictated. Building engineers or security guards may not be able to assist in this effort, due to the tenant's desire to control all access to their space for security purposes.

Cautious Sequence of Action Involving Tenant UPS Systems, Safety First!

  1. Determine on arrival whether the floor of alarm has a redundant power supply (the building engineer may or may not know for sure, a clue may be the tenant, such as telecom, banking or trading firms) and always approach the floor from the stairwell, never the elevator, using extreme caution.
If a gaseous special suppression system has activated, always wear SCBA as a precaution before entering the possible fire area. Also be aware that acid mist from battery fires may be present (hydrochloric and sulfuric). If the sprinkler system has activated, be aware that energized equipment may be involved. There may be energized water on the fire floor. All power (primary and secondary utility feeds and back-up tenant systems) should be isolated before entry is made into the fire area. Remember that this may take some time. Do not trust EPO switches, even if they are located outside the computer room. Batteries by their very nature store electrical energy. Even if disconnected from their load by an EPO, the batteries still are dangerous and extreme caution must be used in their vicinity to avoid causing a short with a tool such as a halligan or puncturing the battery vessel and releasing sulfuric acid. Computer cabinets may contain small batteries within the housing that act as an individual unit/stand-alone backup power source, the best extinguishing agent off the fire rig may be CO2 hand-held extinguishers (or even dry-chemical as a secondary choice) with small fires before considering water application. Also, expect very narrow aisles in computer areas that will make team searches more difficult. (Use of CO2 on large wet-cell batteries may cause cracks in the container, resulting in an acid spill due to thermal shock, contrary to MSDS data.) Be careful operating on top of raised floors or under exposed/concealed ceiling grids that may contain considerable amounts of combustible and/or toxic wiring as well as high-voltage cabling. Be cognizant of the increased concentrated floor loading in areas containing batteries that the floor assembly may not have been designed to carry. ALWAYS check the floor above a serious fire for this threat! Be aware of the possible presence of hydrogen gas and its explosive nature. NOTE: VRLA batteries can experience "thermal runaway." If entering battery area and loud whistling noise is heard, leave area immediately as explosion may be imminent! Be aware of sulfuric acid spills involving charging/compromised batteries and the possible lack of containment solutions. Note high-security access to computer rooms (including "man traps") and prepare accordingly before entering (tag lines, rapid intervention teams on standby, personal alert devices turned on, doors chocked fully open, etc.). Work in teams and move slowly, carefully in smoke-charged areas. Maintain physical contact and verbal communication between members. Stay low and listen for hints of danger, arcing, hissing, popping, crackling noises, etc. Fire department radios may not transmit or receive in close proximity to computer equipment due to electromagnetic fields and they may also destroy valuable tenant data. Avoid using radios for non-essential transmissions. Ventilation may be difficult due to possible windowless rooms and stand-alone HVAC (heating, ventilation and air conditioning) systems. Expect smoke to be mostly non-buoyant, "cold" smoke, banking down to floor level. Proprietary sprinkler system shut-off valves may be concealed and difficult to locate. Tenant package air conditioning units may use freon gas as a refrigerant. If this is released during a fire, generation of phosgene gas may occur. SCBA must be worn. Hazmat units should be dispatched immediately upon verifying working incident. Emergency action plans should be created prior to incident unfolding.


Has the time come to seriously consider rewriting your high-rise standard operating procedures (SOPs)? UPS systems are becoming more and more prevalent. In the north tower of the World Trade Center, Cantor Fitzgerald had a very large UPS system on the 110th floor feeding its trading floors on the 104th and 105th floors. There were many such systems that took up 10,000 square feet or more with batteries and UPS systems. It should be understood that most building engineers may have very limited knowledge as to what is actually in these unique tenant occupancies, since they do not maintain them. They also were likely not involved with the installation of specialized equipment contained within these high-rise office floors.

Some engineers, however, are very well versed in everything going on in their buildings and should be tapped as invaluable resources of strategic information before fireground tactics are initiated. Their knowledge may prove to be the difference between life and death for first responders entering and operating in potential high-danger areas. What you do not know truly can be fatal.

Next: Building redundant power supplies.

Curtis Massey is president of Massey Enterprises Inc., the world's leading disaster planning firm. Massey Disaster/Pre-Fire Plans protect the vast majority of the tallest and highest-profile buildings in North America. He also teaches an advanced course on High-Rise Fire Department Emergency Operations to major city fire departments throughout the U.S. and Canada. Massey also regularly writes articles regarding "new age" technology that impacts firefighter safety. A very special thanks to the technical expertise and contributions of Chris Japhet, Bob Taylor, Steve Boos, Nick Giannak, Alan Reiss (former director of the World Trade Center) and Jim Jenkins.

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