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February 1, 2024
A high-rise building is a complex structure requiring special fire protection and life safety considerations. This blog explores three fire safety challenges in high-rise buildings and offers solutions for protecting your property and occupants.
Before we dive into the fire safety obstacles, let’s define a high-rise building.
According to the National Fire Protection Association (NFPA) 101 Life Safety Code and the International Building Code (IBC), a high-rise is “a building where the floor of an occupiable story is greater than 75 feet (23 m) above the lowest level of fire department vehicle access.” This is the generally accepted definition of a high-rise building; however, it does vary by location based on local amendments. For example, in Clark County, Nevada, the threshold is only 55 feet before high-rise code requirements apply. This deviation is usually due to the firefighting capabilities of the local jurisdiction.
High-rise buildings are architecturally and structurally complex. To ensure fire safety, you must understand the unique obstacles posed by high-rises and how to resolve them.
In high-rise buildings, the risk of rapid fire and smoke spread is notably heightened due to the vertical nature of their architecture. Stairwells, designed for vertical pedestrian movement between floors, can inadvertently facilitate the upward movement of smoke. Additionally, elevator shafts can contribute to the rapid spread of fire throughout the building due to their vertical alignment and the potential for the shaft to act as a chimney-like conduit for smoke.
One of the most infamous examples of fast fire and smoke spread is the MGM Grand fire, which occurred on November 21, 1980. Although the fire was limited to the first floor of the hotel, toxic fumes and smoke spread throughout the building via elevators and stairwells. The fire resulted in 87 deaths, mostly due to smoke inhalation, specifically on the upper levels.
Combustible cladding, which is a building material used in the exterior of structures, is another major problem that leads to fast fire spread. Cladding is often chosen for its aesthetic qualities, insulation properties or cost-effectiveness, but its combustible nature poses significant fire safety risks.
For example, the Grenfell Tower fire of 2017 proved the danger of using combustible cladding. The fire started due to an electrical fault in a refrigerator on the fourth floor of the building, and it quickly spread due to the presence of combustible cladding on the exterior. As a result, 72 people lost their lives.
Several key measures must be implemented to prevent the spread of fire and smoke in high-rise buildings:
Working with a fire protection engineer from the beginning stages of design can help to ensure a coordinated plan for life safety systems and identify any potential oversights that may cause permitting delays. You can trust a fire protection engineer to provide guidance during construction to ensure an expedient certificate of occupancy (CO) for your high-rise. Fire protection engineers also provide ongoing testing/inspections of smoke control systems to maintain life safety post-occupancy. From feasibility through occupancy and throughout the lifespan of a high-rise building, a fire protection engineer is a critical member of the team.
Evacuating a high-rise building presents several hurdles, and human behavior plays a large part. Occupants typically require at least two cues to initiate an evacuation, such as smelling smoke and hearing a fire alarm. If only one cue is present, occupants might disregard it. People are also desensitized to fire alarms, making them more likely to believe the alarm is merely a test instead of a threat.
In addition, people tend to act altruistically during emergencies, risking their safety to assist others in danger. While this altruistic instinct shows community spirit, it can complicate evacuations by slowing down evacuation procedures, posing risks to both occupants and first responders.
Phased evacuation strategies emphasize the importance of proper design and reliability of fire protection and life safety systems in high-rise buildings. Phased evacuation often involves evacuating the fire floor, the floor above and the floor below, although this approach can vary by jurisdiction. In theory, this mitigates the congestion of stairwells compared to if everyone attempts to evacuate simultaneously, allowing for quicker evacuation and better firefighter access.
When fire protection and life safety systems fail due to improper design, construction or maintenance, the ability to evacuate safely is compromised. The Grenfell Tower incident is a tragic reminder of what can occur when fire safety systems and strategies fail. In this situation, an attempted phased evacuation urging occupants to shelter in place went terribly wrong.
There are several ways to streamline evacuations in high-rise buildings. Exit stairs are the most important element of egress for highrise buildings. There are 4 main considerations to optimize their effectiveness – location, capacity, protection, and identification.
By strategically locating and properly sizing the stairwells, the risk of congestion during evacuation is reduced, thereby facilitating a smoother and more organized exit process. These dedicated exit stairways are also protected by pressurization systems and fire-rated barriers, which maintain a controlled environment within the stairwells, preventing the infiltration of smoke and ensuring a clear and safe pathway for occupants seeking to exit the building swiftly. And finally, by installing fire safety signage, including prominent exit signs and comprehensive egress plans in all units, occupants are guided to exit stairs to evacuate the building.
Fire safety access elevators are mandated by IBC 403.6.1 for buildings with occupied levels above 120 feet. These dedicated elevators allow first responders to access floors faster and evacuate occupants in the event of a fire. They also offer direct access to stairs that have hose valves. First responders can use the stairs as a call stage to set up their hoses and strategize how they want to combat the fire. When it’s time to egress, first responders and occupants can reliably exit through the fire service access elevator lobby, which has direct access to an enclosed interior exit stairway or ramp.
Another critical element of evacuation is prompt and clear communication – both for first responders and to provide instruction for the occupants of a high rise. By implementing an emergency voice alarm communication (EVAC) system, clear voice instructions can be provided to targeted zones of a high-rise building, thus facilitating a phased evacuation strategy. Studies have also found that occupants respond more reliably to a voice command compared to the chirping of a traditional fire alarm system.
For first responders, bidirectional amplifiers (BDA systems) are designed to enhance and ensure the effectiveness of radio signals by amplifying and boosting signals in both directions, enabling reliable communication during emergency situations in highrise buildings. The design of a BDA system involves testing the signal strength before and after building construction; if the signal strength is significantly diminished, then large antennas are provided on the roof, with smaller antennas distributed throughout each floor designed to optimize communication for firefighter response.
Water pressure poses a significant challenge for high-rise buildings due to the unique demands imposed by their vertical structure. In tall buildings, water must be supplied to upper floors for various purposes, including manual firefighting and automatic sprinkler systems. However, as the height of the building increases, the pressure required to pump water vertically also escalates.
It takes 0.433 psi to overcome one foot of vertical elevation. So, for water to be pumped to the top of a 400-foot tall building, you would need more than 173 psi of water pressure to overcome elevation alone, not to mention the pressure loss due to internal friction of the pipe or the minimum required pressure for the sprinkler or hose connection.
Class I standpipes require a minimum pressure of 100 psi, as mandated by the code, to ensure that firefighters have enough water pressure to fight fires adequately. For that same 400 ft tall highrise building, you now require over 273 psi at the base of the building to adequately supply the top hose connection. Inadequate water pressure can compromise the effectiveness of firefighting efforts, rendering sprinkler systems and standpipe systems less efficient and potentially impeding the ability to control or suppress a fire.
However, it’s not just low pressures that are a problem; you need to be mindful of the maximum rated pressure of fire protection equipment. Most components of a sprinkler system, like sprinkler heads and valves, are rated to a maximum of 175 psi.
To fight a high-rise fire, firefighters can’t utilize attack lines, which are normally connected to the pumping engine for low-rise buildings. Instead, they carry hose bundles to attach to a permanently fixed standpipe hose valve, typically a floor or two below the fire floor. These hose valve connections are too dangerous to operate at high pressures. Maintaining consistent and sufficient water pressure throughout a high-rise building is crucial for ensuring effective fire protection measures.
To maintain water pressures within a useful range, a fire pump is provided with sufficient capacity to satisfy the greatest demand. Then, a strategy to reduce pressures so as not to exceed equipment ratings must be implemented. This is typically accomplished through a zoned or point-of-service approach with pressure-reducing valves to regulate water distribution effectively throughout the high-rise building.
Pressure reduction by zone is desirable for highrise buildings on the taller side – 400 feet plus. This approach reduces the total number of pressure-reducing valves (PRVs), thus significantly reducing the ongoing effort required for regular testing.
Point-of-service pressure reduction is accomplished by providing PRVs at each sprinkler riser and hose valve connection. This method maintains the most consistent water pressure by adjusting and controlling each floor's pressures.
Safeguarding high-rise buildings from fire risks requires a comprehensive and integrated approach. By understanding and addressing the unique challenges associated with these structures, stakeholders can create safer environments, emphasizing the importance of collaboration, proactive planning and adherence to fire safety standards.
Protect your high-rise building with smoke control services and fire and life safety system design from Performance Based Fire Protection Engineering. Our experts have the knowledge and skills necessary to keep your property and occupants safe in the event of a fire. Contact us to start the conversation.
