Firefighting Operations in Mid-Rise Office Buildings

By John Norman

Firefighters in many suburban areas are encountering a new type of structure in their response areas—the mid-rise office building. It is often erected seemingly overnight in a newly created “office park” in what last week was a cornfield. Below, I will describe the structure’s features, the difficulties that these features create, and the firefighting tactics needed to deal safely with a working fire in such an occupancy.

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What Is a Mid-Rise?

A mid-rise structure is one that is taller than a low-rise (one or two stories high) but not tall enough to meet the code description of a high-rise (typically seven stories or 75 feet high). A mid-rise then is a structure three to six stories high. Many fire departments have had three- to six-story apartment buildings in their communities for decades and are experienced at fighting fires in them but are still unprepared for fighting a fire in the office structure of the same height because of the many differences between the two occupancies. Most fires occur in residential occupancies, which gives us our experience and helps us to develop our tactics, but this also sets us up to fail if we try to use those same tactics in a different occupancy.

(1) A mid-rise office building is a serious challenge to manual firefighting, with problems unlike other structures in most communities. (Photos by author.)

In some ways, the unique conditions found in a mid-rise make fighting a fire in one more difficult than a similar fire in a true high-rise because many fire protection features required by code for a high-rise are absent. Common deficiencies include the use of combustible construction (Class 3) and lightly protected steel (Class 2) methods in mid-rises, as opposed to Class 1, which is usually required when buildings exceed 75 feet. In addition, depending on when the building was built and what code was in place at that time, the building may not have sprinklers installed and may not even have a standpipe system that taller buildings require.

The Differences

Having successfully fought apartment fires in many mid-rise apartment occupancies has taught us that a single mid-sized handline (1½-, 1¾-, or two-inch) is typically very successful in extinguishing the average apartment fire if it can be quickly stretched to the seat of the fire and placed between the fire and any endangered occupants. This is largely because of several factors found in these occupancies—relatively small room sizes, compartmentation of the apartment by fire-resistant walls separating the fire area from other spaces, relatively light fire loading compared to commercial occupancies, and a potentially high life hazard, particularly at night.

Firefighters responding to a working fire in an office structure must understand that none of those factors are likely to be found. Office workers are (usually) awake when in the structure and flee when fire threatens, even at night. That should prompt firefighters to behave much more cautiously than if they had responded to a fire in an occupied residential structure with people trapped. Floor areas are largely undivided spaces, often 10,000 square feet or more, and the fire load per square foot can be much heavier than in typical living areas, meaning that the 1¾-inch hoseline that works so well in the apartment house will be terribly outgunned when encountering a large fire on one of these office floors.

(2) Many mid-rise offices are built with Class 2 construction, which more readily allows fire spread from floor to floor than Class 1; this also poses the danger of structural collapse.

Other factors that make the commercial fire so different from residential fires include few or no occupants after business hours to detect and combat incipient fires and a potential lack of fire protection devices, such as smoke detectors and automatic sprinklers. The result is often advanced fire on arrival. These occupancies often include high ceilings with plenums above them. Firefighters have been trapped by rapid fire spread over their heads in these occupancies. The high ceiling allows large quantities of smoke consisting of unburned fuel gases to build up over their heads unrecognized until it is too late. When this smoke is heated to the proper temperature, great waves of fire will roll overhead along the ceiling. Unless a sufficiently large hosestream is present to cool and quench these gases, the ignition will overrun the firefighters, causing a flashover of the area.

The same can occur in the plenum space above the ceiling, where most of the utilities are run—e.g., air conditioning supply ducts, wiring, and light fixtures. These can collapse on firefighters operating below.

The size of the floor areas present usually demands at least two and often many more separate exit stairs; this is good and bad. It is good because it allows multiple escape routes but also compounds operational problems. Initial-arriving units must quickly size up the structure, determine the construction type and anticipate the likely fire extension and collapse issues associated with each, locate the seat of the fire, and then select the correct stair to use as the attack stair. We should generally use the stair nearest to the seat of the fire as the initial attack stair, but several factors affect that choice. Are civilians above the fire using it as the evacuation stair? Does it have a standpipe riser? What happens when the door to the fire floor is opened; will fire be forcefully drawn toward the door? The availability of multiple stairs also creates the possibility of opposing hose streams that will drive fire toward other units if not carefully controlled.

(3) Office occupancies are often a confusing maze of cubicles and perimeter offices. The large, open areas are very conducive to rapid fire spread, which can overrun firefighters crawling at floor level. Using a search guide rope helps firefighters avoid getting lost in these situations and speeds retreat.

The large undivided floor areas that are often present add another layer of difficulty that firefighters who have only dealt with residential fires before are often unprepared for: Extremely large spaces require a longer-duration air supply. Many fire departments still use 30-minute air cylinders in their self-contained breathing apparatus (SCBA), which are satisfactory for a residential fire that is confined to the apartment of origin but which leave firefighters with an inadequate supply of air in large floor plan areas where the members may be a long way from fresh air when their low-air alarm sounds. Fire departments that may be called on to fight fires in large floor plan office buildings should invest in longer-duration air cylinders—45 or 60 minutes—for their personnel to reduce the chance that they will run out of air while still in a dangerous atmosphere.

Another tool that we should consider essential for operations in these structures is a search guide rope for every search team. The large floor spaces in these structures often use head-height partitions separating each work space. These “cubicle farms” can be very confusing in a heavy smoke condition, while the open space between the top of the partition and the ceiling allows rapid fire spread in a developing fire. The search guide rope, secured in the stairwell, will allow the team members to quickly follow it to safety if they need to retreat under rapidly deteriorating conditions.

The good news about firefighting in mid-rise buildings, in some cases, is that the fire should be within reach of aerial ladders and platforms for access, ventilation, and rescue and for master stream application if needed (not possible on the 30th floor of a high-rise). The bad news is that this is not always true, even if the building is only four or five stories high. Building setbacks and terrain features found in many of these newly created office parks sometimes prevent fire department apparatus access, even if they are less than 75 feet high. Often, this occurs when the structure is surrounded by parking structures that allow cars to drive right up to the building. However, for aerial apparatus, the parking structure’s height clearance is too low and the parking deck is too weak to support the apparatus’ weight, so it can’t be used to get near the building. Make sure the local zoning and fire prevention officials understand the critical nature of ensuring fire department apparatus access to all portions of every structure that is not a “highly protected risk”—i.e., it is built with Class 1 construction and is equipped with a fully operational wet pipe sprinkler system throughout the structure. Otherwise, you may find yourself out of options if a working fire develops.

When planning for or responding to commercial fires, all members must recognize the factors described above and take the necessary actions to prevent a tragedy. Actions include the following:

Adjust the pace of activities. Rarely is there a civilian life hazard. Make certain everyone knows that protecting life, including firefighters’ lives, is the highest priority, even if flames are blowing out into the street. Act deliberately and cautiously, and make sure we all go home in one piece.

Attack the fire with a flow large enough to ensure a quick knockdown. Leave the 1¾-inch lines on the rig, at least initially. Plan for a high-volume attack with 2½-inch handlines, master streams, or both. Use the reach of these streams to keep your people out of dangerous areas—e.g., where heavy volumes of highly heated smoke indicate it is about to “light up” or where lightweight steel construction presents a collapse hazard. Use of positive pumping (pumper located on the hydrant) or large-diameter supply lines is required to ensure needed flows.

Supply the siamese connections of all firefighting systems early and from an adequate source, at the proper flows and pressures. This may mean committing additional engine companies to water supply.

Withdraw personnel to defensive positions earlier than you would in an occupied building. Do not be afraid to write off property if it requires putting firefighters at great risk. We must conduct a primary search in every structure, but in a building with a very low probability of trapped civilians, this search should be tempered with a great deal of caution. Of course, if there are indications that there are people trapped, firefighters should behave as aggressively as warranted to save those lives, but please weigh the risks before committing to extremely dangerous actions.


John Norman is deputy assistant chief (ret.) of the Fire Department of New York.

John Norman will present “Fire Operations at Mid-Rise Office Buildings” at FDIC International in Indianapolis, Indiana, on Wednesday, April 27, 2022, 1:30 p.m.-3:15 p.m.

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