Engine Essentials: Initial Handline Considerations for Commercial Fires
Commercial building fires present unique challenges for responding engine companies. The size of the structure combined with the fuel loads that are present in these occupancies can create a formidable opponent under fire conditions. These fires require strategic handline placement, high rates of water application and methodical advancement into the structure.
According to the U.S. Fire Administration’s (USFA) report, “Fire in the United States 2008–2017,” nonresidential building fires constituted only 7 percent of the total fire problem in 2017, the most recent year for which data are available. (Residential structure fires outnumbered nonresidential structure fires by more than 3-to-1.) Unfortunately, these low-frequency, high-hazard fires statistically result in more line-of-duty deaths than residential fires. A 2020 NFPA report that examined firefighter deaths per 100,000 structural fires indicated, “There were 3.0 fireground deaths per 100,000 nonresidential structure fires from 2014 through 2018, compared to 2.7 deaths per 100,000 residential structure fires.”
The higher frequency of residential structural fires causes many departments to default to tactics that are utilized for dwelling fires even when combating nonresidential building fires. Recent UL Firefighter Safety Research Institute (UL FSRI) studies showed that fires in commercial buildings react differently because of fuel loads and building characteristics than fires in residential buildings. Departments must develop strategies and tactics that are specific to commercial building fires.
Occupancy, fire characteristics
Building characteristics and fuel loads directly affect fire growth and development. Engine companies often arrive to find nothing evident from the exterior in regard to heavy fire conditions. Commercial buildings frequently have large-square-footage floor plans, lack compartmentation and have high ceilings. These specific building features can mask the severity of a fire because of the larger interior volume that smoke and products of combustion must fill before they vent through natural openings.
These large-volume spaces also contribute to rapid fire growth because of the oxygen levels that are available in the space. The 2020 study by UL FSRI, “Exploratory Analysis of the Impact of Ventilation on Strip Mall Fires,” looked at the potential energy that can be released in certain size volumes prior to the oxygen dropping to 15 percent. The study found that a single-story ranch home (9,568 cubic feet) could release slightly more than 250 Megajoules (MJ) prior to the heat release rate being affected by low oxygen levels. Compare that to a large strip mall (63,000 cubic feet), which could release roughly 1,800 MJ prior to being affected by low oxygen levels.
Available oxygen coupled with high fuel loads can generate extreme fire conditions. The amounts of fuel that are available fluctuate depending on the type of occupancy. The fuels can vary from grease in fast-food kitchens, to plastic electronics in offices, to high-racked shelving in retail spaces, to flammable liquids in vehicle repair shops. Further, the fuels often are placed in close proximity to one another, which allows the fire to rapidly spread.
The 2020 UL FSRI study of ventilation at strip malls included an experiment in a 70-foot-wide by 60-foot-deep strip mall unit. The fuel package was ignited near the middle of the structure, and the front door was left in the open position. Temperatures in the fire compartment peaked at three minutes and thirty seconds after ignition. Thermocouples in the AB, AD and CD quadrants of the structure showed homogenous floor-to-ceiling temperatures in excess of 1,200 degrees F. Temperatures in the BC quadrant, which was farthest from the door and the ignition, remained stratified, with temperatures ranging from 800 degrees F at 2½ feet above the floor to 1,200 degrees F at one inch below the roof deck.
Floor-to-ceiling temperatures in excess of 1,200 degrees F throughout the 4,118-square-foot space are indicative of flashover conditions. The sheer size of this compartment coupled with the intense fire conditions throughout the space require fire streams with increased reach and gallon per minute (gpm) flow rates to effectively cool the space. Engine companies must be prepared to immediately flow their handline as soon as the door to the compartment is opened in an attempt to reduce fire growth that occurs with increased oxygen.
Handline size, flow rates
Because of the amount of water that must be flowed to combat fire conditions, a 2½-inch, or the newer 2¼-inch, hoseline should be considered the handline for commercial fires. However, engine company officers must not forget other options, such as deck guns or portable master streams, depending on the conditions that are present on arrival. If necessary, handlines should be stretched to attached exposures for protection. For the sake of this article, we will focus on the initial handline in the building of origin.
Handline flow rates for commercial buildings should be in the range of 250–300 gpm. The rationale for this is twofold: increased fuel loads present in the building and longer distances that the stream must travel in the structure. As noted above, commercial structures tend to have higher fuel loading than residential structures solely based on the square footage. These occupancies also might have fuels that typically aren’t present in residences, such as hazardous/flammable chemicals. All of these additional fuels require higher flow rates than that of the industry standard of 150 gpm for residential fires.
The 2½-inch handline stream, specifically from a smooth bore nozzle, provides a greater mass of water than that of a stream that’s generated from a 1¾-inch handline. This increased mass allows the stream to be carried greater distances into the building. As the stream passes through the superheated environment, it’s converted to steam. This conversion to steam causes some gas cooling, but the goal is to extinguish the base of the fire. If the stream only cools the gases, it simply treats a symptom of the fire and not the root cause. A larger mass stream can deliver more water deeper into the structure prior to being converted to steam. Stream mass is the reason that two 1¾-inch hoselines flowing 150 gpm each don’t equal the 300 gpm that’s delivered by a single 2½-inch handline.
Hose placement, entry
The point of entry for the initial handline must be selected after a thorough size up. The size of the structure coupled with mazelike conditions easily can disorient an engine company that operates inside of the structure. The engine company officer must select an entrance that achieves the tactical priority based on the life hazard: handline placed between the fire and evacuating occupants and/or handline advanced through the closest door to the area of origin.
To determine the best entry point, strong consideration must be given to the common causes of fires in commercial buildings. The USFA’s 2020 report looked at the causes of fires in nonresidential buildings. “For nonresidential building fires, three causes accounted for at least half of the fires: Cooking was the leading cause of fires (30 percent), followed by other unintentional or careless actions (11 percent) and intentional actions (10 percent).” Often, kitchens, electrical panels, HVAC systems and other mechanical equipment are housed near the rear of the building.
This makes entry on the C side of the building, or the area that’s closest to these common areas of origin, desirable. The C side of commercial buildings often poses forcible-entry challenges, as these entry points are less visible to passing motorists, thus more attractive to burglars who attempt entry. Rear doors often are fortified heavily after hours to deter potential thieves. Engine companies should bring forcible-entry tools or partner with other companies that are on scene to gain access to the structure. Although it might take some time to force entry, the hoseline still will reach the area of fire origin faster because of the time that it takes to advance a large handline through these structures.
Engine companies should minimize long hoseline advancements through shelving/cubicles that can tip over easily simply from the hoseline catching a corner, which potentially could trap members. The advancement of a large handline in heavy smoke and/or fire conditions must be slow and methodical. The engine company officer constantly must be aware of the distance that the company has advanced into the structure, the time that it will take to exit the structure and the company’s air supply.
Effectively cooling a large-volume building takes time and might come with some unintended consequences. In the UL FSRI study, researchers found that extinguishing the flames at the front of the unit allowed the oxygen entering the front to travel farther into the compartment before being consumed. This resulted in an increase in the rate of combustion deeper in the structure.
Therefore, it’s critical that the engine company officer select the closest entry point to the fire, advance slowly while flowing to cool the environment and constantly be aware of changing conditions throughout the space.
Recognize differing tactics
Commercial fires pose challenges to engine companies that require different tactics than residential fires. Engine company officers must thoroughly size up the building and conditions to determine the best course of action to safely and effectively extinguish the fire. Based on the smoke and/or fire conditions that are present, a minimum of a 2½-inch handline should be stretched. If there are concerns that a 2½-inch handline might not be sufficient, a deck gun or portable master stream device should be employed.
The decision on where to place the first handline must be evaluated carefully based on life safety hazards. The initial handline should be placed either to protect evacuating occupants or at the entrance that’s closest to the area of origin.
Handline advancement into the structure must be slow and methodical to ensure that the large-volume space is cooled effectively. The engine company officer must constantly be aware of conditions on all six sides that surround the company members’ advance.
Although fires in commercial structures aren’t as common as residential buildings, engine companies must develop strategies and tactics that work for their buildings and staffing levels. As always, engine companies should get out into their district, become familiar with their buildings and train on the use of large handlines.
Jonathan Hall
Jonathan Hall, who is a Firehouse contributing editor, has more than 23 years of fire service experience. He currently is a captain with the St. Paul, MN, Fire Department assigned to Engine Company 14. Hall also serves as a lead instructor in the department's Training Division; he teaches hands-on skills to members of all ranks. Hall is the co-owner of Make The Move Training LLC and teaches engine company operations throughout the country.
