Some of the most important fire safety features in buildings are those you cannot see. Passive fire protection (PFP) is an integral component of the comprehensive fire protection systems that keep us safe in the buildings in which we live, learn, work, and do business in.
PFP is designed and incorporated into the structure of buildings to protect occupants and minimize fire damage. PFP consists of several different structural elements that work together to help prevent the spread of fire and smoke throughout the building.
Passive fire protection has been a part of building codes for most of the 20th century and over that time has continually improved with advancements in fire science and construction techniques as well as the availability of new and better building materials.
Buildings today are required to be designed, engineered and constructed with PFP in mind. This post will introduce you to one of the most important elements of PFP – the firewall. And, when you're finished reading it, you'll not only know more about firewalls, but you might also be surprised at how much safer you are because of them.
What a Firewall is (and what it isn't)
Like other types of PFP, the primary purpose of a firewall is to slow the spread of fire and smoke from one area of a building to another, giving occupants more time to escape and confining the fire where possible.
The National Fire Protection Association (NFPA) 221 Standard for High Challenge Firewalls, Firewalls, and Fire Barrier Walls defines a firewall as a wall separating buildings or subdividing a building to prevent the spread of fire while maintaining structural stability and offering fire resistance.
Firewalls are not to be confused with fire barrier walls or fire partitions, which are used to subdivide portions of a building contained within a firewall. Like firewalls, these structures are fire resistant and help to protect against the spread of fire. But, they do not provide the structural stability like firewalls.
"High fire challenge" firewalls are a special type of firewall identified in the NFPA 221. They serve the same purpose as regular firewalls, except that they have enhanced fire resistance ratings and other protections designed for buildings that involve the production or storage of things such as explosives, highly flammable materials, and toxic materials. High fire challenge firewalls are also used for warehouses that contain large amounts of combustible materials that can result in long, sustained fires if ignited.
Buildings within Buildings
Firewalls are fire-resistant structures -- usually made of concrete, concrete blocks, or reinforced concrete -- designed to restrict the spread of fire by means of compartmentalization.
The key defining feature of firewalls are their structural independence. Firewalls, in effect, create completely separate, independent structures within a building. With firewalls in place, if one section of a building becomes structurally unstable during a fire, that section can break or fall away from the other sections protecting their occupants from the collapse.
Firewalls can also be designed with a fire resistance rating of up to four hours. The fire resistance rating is the amount of time in minutes or hours that a firewall can withstand exposure to fire. So, while you can't really see the firewalls in a building, you can be confident they are there protecting you by virtue of their structural integrity and fire resistance, which gives you more time to escape in the event of a fire.
Different Types of Firewalls
There are three main types of firewalls that can be used in different situations to achieve the necessary structural stability. These are double firewalls, cantilevered firewalls, and tied firewalls. All three types must be non-load-bearing walls, meaning they carry only their own weight. A brief description of each is provided below.
A double firewall consists of two, back-to-back walls with no connection other than flashing between them. Each wall is supported laterally by the building frame on its side and is completely structurally independent from the firewall next to it and the building frame on the other side.
Double firewalls are often used where an addition to a building requires a firewall between an existing structure and a new building. With a double firewall, the existing wall, which is already connected to the frame of the building is altered if necessary to provide the required fire resistance and protection for that section while a new firewall is constructed adjacent to it and connected to the frame of the new building. With each wall connected to separate structural frames, each is completely independent of the other.
Cantilevered firewalls are free-standing, self-supporting walls connected only at the foundation. Because this type of firewall is dependent on vertical reinforcement, its height is generally limited. In some cases, masonry pilasters may be used to enhance their lateral resistance, however, at heights greater than about 32 feet, a tied firewall is more suitable.
Tied firewalls get their lateral stability from the building frame. As the name suggests, tied firewalls are fastened to and usually encase members of the structural frame of the building, with both walls connected separately to the building frame on either side.
In the event of a fire, the pull of the collapsing structural members on the fire side of the wall is resisted by the strength of the structure on the other side. Because a fire can occur on either side of the wall, it is important that each side have the same structural strength as the other to prevent one from collapsing into the other. In order to achieve this, tied firewalls are generally located in the center of the building where the strength of its frame can be equally divided between the two walls.
Features Common to All Firewalls
There are several basic features that are common to all firewalls, regardless of their type. For example, firewalls generally extend from the foundation of the building to at least 30 inches above the surface of the roof, although NFPA 221 does include some exceptions based on the type of construction used in the building. Horizontally, firewalls must be continuous in one of the following ways:
- From one exterior wall to another exterior wall and extending at least 18 inches beyond the outside surface of the exterior wall
- From an exterior wall extending from at least 18 inches beyond the outside surface of the exterior wall to another firewall with the same fire resistance rating
- From one firewall to another firewall with the same fire resistance rating
All openings must also be protected with firestop systems or devices, and they can have up to a 4-hour fire resistance rating. Firewalls cannot be load-bearing and must be designed to:
- Remain freestanding if the structures on either side of it collapse
- Resist the fracturing, penetration and fragmentation that a fire can cause
- Include expansion or control joints to help prevent the wall from buckling under rising temperatures during a fire, which can cause thermal expansion of the wall
- Withstand other forces acting upon the wall such as the fall, collapse or expansion of the adjacent structure or stored items within the structure itself
In addition, firewalls are required to be designed and constructed with materials that have met the requirements of the American Society for Testing and Materials (ASTM) E119 Standard or the Underwriters Laboratory (UL) 263 Standard, both of which provide guidelines for fire testing building construction and materials.
Perhaps the most important feature common to all firewalls is that they help make our buildings safer. There's really no way to know how many lives have been saved since the first building with firewalls was constructed many decades ago. But, they remain an integral part of passive fire protection systems – systems that work 24/7 behind the scenes to minimize damage that fires cause, and give occupants precious extra time to get out of the building safely.
Koorsen is Here to Help
Contact Koorsen today if you have questions about firewalls or any other type of fire protection required for new building construction and renovation projects. Our experts are ready to assist.