Based on the 2021 International Building Code, a high-rise building is a building with an occupied floor located more than 75 ft above the lowest level of fire department vehicle access.

Due to their height, fires in high-rise buildings represent a unique challenge to the fire services for a number of reasons. Difficulties including evacuating the building occupants, getting fire-fighters, medical personnel if needed, and the necessary equipment to the vicinity of the fire floor, accessing the fire for firefighting purposes, ventilating the building, and communicating with the fire command center all complicate the process of fighting high-rise building fires.

As a result of the difficulties of fighting high-rise building fires, the model building code writers have long since recognized the need to rely on robust passive building construction methods and active fire protection equipment in high-rise buildings.

On the passive fire protection side, the codes require fire-resistance-rated construction to provide both structural fire resistance and building compartmentation, protected means of egress, the protection of breaches in fire-resistance-rated construction, the use of interior finish materials with low flame spread and smoke development characteristics, and more recently an additional stairwell and dedicated fire services emergency elevators.

On the active fire-protection equipment side, the code requires automatic sprinkler systems, standpipe systems, portable fire extinguishers, fire alarm and detection systems, smoke control systems, smoke and heat vents, fire department connections, fire pumps with protection from interruption of service, and standby and emergency power.

The model fire codes have also recognized the need for maintaining passive and active protection systems for the building life cycle to assure they will work properly if and when needed. For the most part, these systems are required to be inspected and/or serviced on an annual basis.

The specific protection requirements for both active and passive fire protection are based on what the building codes define as the Occupancy of the building and the Type of Construction.

Chapter 3 of the International Building Code defines the Occupancy of the building. For example, a Business Group B Occupancy covers a building or structure, or portion thereof intended for office, professional and service-type transactions.

A Residential Group R-1 Occupancy covers transient sleeping units such as hotels and motels. Each of the twenty or so occupancies essentially assign a risk associated with that occupancy.

The higher the risk, the more limitations applied to the building. As an example, a Business occupancy is inherently a lower risk than a R-1 Residential use covering transient hotels. In a business occupancy it is assumed the occupants are awake and alert and are familiar with their means of egress. That may not be the case with a hotel. As such, a building constructed for a Business Occupancy is permitted to be larger than one constructed for a R-1 Occupancy.

Chapter 6 goes on to define five basic Types of Construction. The five types of construction are as follows:

• Types I and II. Types I and II construction are those types of construction in which the building elements are of noncombustible materials, with certain exceptions.
• Type III. Type III construction is that type of construction in which the exterior walls are of noncombustible materials and the interior building elements are of any material permitted by this code. Fire-retardant-treated wood framing and sheathing complying is permitted within exterior wall assemblies of a 2-hour rating or less.
• Type IV. Type IV construction is that type of construction in which the building elements are mass timber or noncombustible materials and have a fire-resistance rating.
• Type V. Type V construction is that type of construction in which the structural elements, exterior walls and interior walls are of any materials permitted by this code.

Each type of construction also includes a letter designation defining the protection required for that designation. Other than for Type IV construction, the letter “A” refers to “protected” construction and the letter “B” to “unprotected” construction. Although those terms may not be completely accurate, an “A” designation typically requires a higher fire-resistance rating and more fire protection systems. Putting the Type of Construction together with the letter designation, a Type IA building is noncombustible, and is required to have the longest fire-resistance rating and the most robust package of fire protection features. As such, it is permitted to be larger and taller than remaining types of construction.

Table 504.3 of the IBC specifies the allowable building height above grade plane. This table would suggest high-rise buildings are required to be of a Type I, II or IV Type of Construction. Although Type IV construction appears to be out of place for this application, protected heavy timber does well under fire conditions and as such after much scrutiny was included in Table 504.3 at allowable heights which meet the definition of a high-rise building.

Table 601 of the IBC defines the required fireresistance rating of the building elements based on the type of construction.

Putting all these facts together and ignoring some additional modifying factors, as an example, a Type IA building, used as a R-1 occupancy (i.e., a hotel), protected with an NFPA 13 automatic sprinkler system is permitted to be of an unlimited height and area and is required to have the primary structural frame rated for a 3 hr fire-resistance rating. Likewise, the remaining building elements other than interior nonbearing walls and partitions are required to have a fire-resistance rating.

There are multiple other applications requiring fireresistance ratings beyond the building elements specified in Table 601. Examples include fire walls creating separate buildings, fire barriers used to separate occupancies and create shaft enclosures, fire partitions used to separate dwelling / sleeping units and protect the means of egress. –

Once the required fire-resistance rating is known, Section 703 of the 2018 IBC provides three basic methods of demonstrating fire-resistance. The three methods include:

1. Ratings determined based on the test procedures set forth in ASTM E119 or UL 263, “Fire Tests of Building Construction and Materials”.

2. Ratings established by analytical methods based on fire exposure and acceptance criteria specified in ASTM E119 or UL 263. These analytical methods include the use of designs documented from approve sources, prescriptive fire-resistance as prescribed in Section 721, calculated fire-resistance in accordance with Section 722, engineering analysis based on test procedures set forth in ASTM E119 or UL 263, and fireresistance designs certified by an approve agency.

3. Alternate methods based on Section 104.11, “Alternate materials, design and method of construction and equipment”.

The two basic methods of providing fire-resistance to the various building elements are through the use of direct applied or membrane fireproofing.

Direct applied fireproofing can take the form of sprayed fire-resistive materials (SFRM) or intumescent fire-resistive materials (IFRM). As the name would imply, direct applied fireproofing is typically applied directly to the building element such as a column, a beam, a floor or roof deck, or sometimes a wall assembly.

These products – SFRM & IFRM - serve to insulate the building element from the heat of the fire, thereby keeping the temperature of the element in a range where it will maintain its structural integrity and/or will limit the transfer of heat through the element.

Membrane fireproofing consists of proprietary board products, flexible wrap products, gypsum board and acoustical ceilings. While the intent of those products is also to insulate the building element from the heat of the fire, their application is somewhat different. Instead of being directly applied to the substrate, they are installed as a membrane and are typically spaced away for the building element some distance. For example, an acoustical ceiling is suspended beneath the structural elements and steel deck of the floor or roof above creating a concealed space.

The specific requirements for a passive protection of high-rise buildings evolved after the tragic events of 9/11. Shortly after this event, the International Code Council’s Board of Directors established an adhoc committee on Terrorism Resistant Building (TRB) which was charged with reviewing and making code change proposals that beef up building construction so as to better resist terrorist attacks. In retrospect, one could argue whether the building code should be addressing such incidents. Never the less, the task group did develop and propose more robust requirements for high-rise buildings.

Some of the provisions submitted by the TRB that were approved for inclusion in Section 403 of the 2009 International Building Code, covering High-Rise Buildings include:

• A higher bond strength requirement for SFRM protection for buildings greater than 420 ft above fire department vehicle access and an increased focus on inspection.
• The separation of adjacent exit stairways.
• Impact resistance of critical exit shafts for safety.
• An additional exit stairway for evacuation of building occupants.
• An additional five service elevator for use by the fire services during fire events.

In addition to the requirements contained in Section 403 of the International Building Code, there are other provisions in the code for materials used to provide fire-resistance ratings regardless of building heights.

Section 704, covering Fire-Resistance Ratings of Structural Members contains requirements for the installation of SFRM. Requirements include the following considerations:

1. The application of the SFRM shall be consistent with the listing, including, but not limited to the minimum thickness and dry density of the material. The method of application, the substrate surface condition and the use of bonding adhesives, sealants, reinforcing or other materials.

2. The application of the SFRM shall be in accordance with the manufacturer’s installation instructions.

3. The substrate to receive the SFRM shall be free of dirt, oil, grease, release agents, loose scale and any other condition that prevents adhesion.

4. Where the material is applied over primers, paint or encapsulants other than those specified in the listing, the steel substrate shall meet certain dimensional requirements and minimum bond strength requirements,

5. The minimum ambient and substrate temperature during and after the application of the SFRM.

6. The finished dried SFRM shall not exhibit cracks, voids, spalls delamination or any exposure of the substrate.

Although not specifically related to fire-resistance ratings, Chapter 25 of the IBC contains requirements for the use of gypsum board. The standard ASTM C1396, “Standard Specification of Gypsum Board”, referenced in Table 2506.2, does provide a definition of Type X gypsum board frequently used in fireresistance-rated construction.

The definition of a Type X gypsum board is a product that provides not less than 1 h fire-resistance rating for boards 5⁄8 in. [15.9 mm] thick or 3⁄4 h fire-resistance rating for boards 1⁄2 in. [12.7 mm] thick, when applied parallel with and on each side of load bearing 2 by 4 wood studs spaced 16 in. [406 mm] on centers with 6d coated nails, 1-7⁄8 in. [48 mm] long, 0.092 in. [2.3- mm] diameter shank, 1⁄4 in. [6.4-mm] diameter heads, spaced 7 in. [178 mm] on centers with gypsum board joints staggered 16 in. [406 mm] on each side of the partition when tested in accordance with ASTM E119.

Sections 1705.15 and 1705.16 of the IBC require special inspections of SFRM and IFRM during and after installation. Special inspections of SFRM are conducted in accordance with the detailed requirements contained within the Section 1705.15. This section covers items such as the surface preparation, temperature requirements before and after application, and thickness, density and bond strength measurements.

Section 1705.16 requires special inspections of IFRM are required to be conducted in accordance with AWCI 12-B “Standard Practice for the Testing and Inspection of Field Applied Thin-Film Intumescent Fire-Resistive Materials; an Annotated Guide”. This document covers items such as site conditions, inspection procedures, methods of tests, visual inspections of the finished applications and patching. Although these items are do not relate to the methods of application, they are significant in assuring the products are installed properly.

As discussed in this article, the primary differences in protecting high-rise buildings relate to the additional passive and active protection required. The actual fireproofing is not significantly different than fireproofing other buildings, although the required rating periods are longer due to the inherent difficulties of evacuating and fighting high-rise building fires.

Written by: Rich Walke
Source: Life Safety Digest
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