Designing For Fire Resistance With Gypsum Panel Systems  

From high-rise commercial towers and institutional facilities to residences and virtually all types of occupied buildings, rapid and safe evacuation of building occupants during a fire or other emergency is of critical importance to life, safety and survival. As the events of September 11, 2001 at the World Trade Center illustrated, the location, materials and fire ratings of exit stairways, vestibule enclosures and corridors leading to them play an important role in ensuring that people can safely exit burning buildings.

Building codes address the need for fire-rated corridors, and fire resistance of materials in certain areas and public spaces within buildings, so that building occupants can reach exits and other means of egress. The codes typically dictate the level of fire resistance a building assembly, or group of components, must meet, and where each assembly shall be located to create the appropriate compartmentalization.

Most municipalities adopt a model code as the basis for their own code, making modifications that best meet their needs. Although many municipalities are switching to the newer International Building Code (IBC), which replaced the Uniform Building Code (UBC), Building Officials Code Administrators (BOCA) Building Code and Standard Building Code, some municipalities still follow one of the three older model codes.

These model codes establish the required fire resistance rating of an assembly based on the intended use of the building and its size. For example, hospitals and high-rise office buildings are considered high-risk structures.

The rapid and safe evacuation of building occupants during a fire is paramount to life, safety and survival. Model codes establish the required fire resistance rating of an assembly based on the building's intended use and size.

Buildings requiring the highest level of fire protection are classified as Type I or Class A. This means that the building must be constructed with non-combustible materials, and all finishing materials must have a limited index for the spread of fire on their surface and the amount of smoke they would emit in case of a fire. In addition, there must be a protected means of egress for building occupants. The means of egress requires that the walls surrounding the area must provide a specific level of fire resistance.

Single-family residences, where evacuation and rescue are generally considered easier to achieve, can be constructed with combustible materials. Multifamily residences typically have fire resistance requirements.

Testing for Fire Resistance

The fire resistance of assemblies is established in accordance with ASTM Standard E119, which is published by ASTM International. Formerly known as the American Society for Testing and Materials, ASTM International is a widely recognized standards development organization.

ASTM Standard E119 provides the ratings for walls and partitions, floor-ceiling and roof-ceiling assemblies, beams and columns. From this nearly century-old test standard, other test standards have been developed to evaluate the level of performance of through-penetration fire stop, joint and curtain-wall systems as they relate to the desired compartmentalization of buildings. The level of fire resistance is measured in hourly ratings: one, two, three, four and eight hours.

ASTM Standard E136 is employed to determine whether or not a given material is considered combustible. This standard measures a characteristic of the material itself, while the former standards evaluated the performance of the assemblies. The surface flammability and the amount of smoke produced by a given material are evaluated in accordance with ASTM Standard E84.

In establishing the fire resistance of an assembly, three factors are taken into consideration: the ability of the assembly to prevent the passage of flame, the capacity of the assembly to limit the heat transfer from the exposed side to the unexposed side and the assembly's ability to maintain its structural integrity for the classification period. Another consideration is the temperature of the structural steel, which may be used to establish restrained and unrestrained ratings.

Walls are required to be subjected to a hose stream test after a portion of the fire resistance test. The purpose of the hose stream test is to measure the relative integrity of the wall after it has been exposed to a fire. Water from the stream is not permitted to project through the wall assembly.

The walls that are to be tested are built within a steel and concrete yoke or frame. ASTM Standard E119 specifies that the area of the test specimen must be a minimum of 100 square feet, with no dimension measuring less than 9 feet. Typically, the test frames are 10 feet by 10 feet. Once the assembly is built within the frame, the frame is clamped in front of the furnace so that one side of the assembly is exposed to the fire.

The temperature within the furnace throughout the test is regulated in accordance with the standard time-temperature curve prescribed in the ASTM Standard.

Standard Time-Temperature Curve

The temperature on the unexposed side is monitored at a minimum of nine locations using thermocouples, which are temperature sensors that can measure a wide range of temperatures. Five of these locations are defined specifically by the standard. One of the thermocouples must be located exactly in the center of the assembly, while the other four must be positioned in the center of the wall quadrants. The location of the remaining four thermocouples is left to the discretion of the lab conducting the fire test.

The average temperature rise on the unexposed surface is not permitted to exceed 250 degrees F, while no single thermocouple is allowed to exceed a temperature rise of 325 degrees F. Load-bearing walls are tested with a superimposed axial load simulating the maximum load condition. The wall must be able to sustain the superimposed load during the fire endurance and hose stream tests. The relative integrity of the wall after a portion of the fire endurance test is determined by the hose stream test.

A second wall is tested to half, but not more than one hour, of the intended fire resistance rating. The fire is shut off, and the partition removed and immediately hit with a specified pressurized stream of water from a distance of 20 feet for a specified period of time that depends on the fire resistance rating. The test requires that this hose stream must be emitted from a 2-1/2-inch hose with a National Standard playpipe nozzle with a 1-1/8-inch tip. If the water does not project beyond the plane of the wall, then the wall passes the hose stream test.

Hose Stream Test

The standards also permit the hose stream test to be conducted at the end of the fire endurance test. It is important to understand that the hose stream test is not intended to simulate what happens when the wall is actually hit with a stream of water from the firefighter hose. Instead, it is only intended to develop data about the relative integrity of the wall after a portion of, or during the entire fire endurance test, so that the design professional can make an accurate assessment of the building's safety.

Fire-Resistive Assemblies

A fire-resistant wall is composed of specially formulated fire-resistant gypsum panels, some type of framing (wood or metal studs), fasteners and a joint finishing system (if it is needed). Fire-resistant gypsum panels are classified as "Type X" in accordance with ASTM Standard C1396.

A 5/8-inch gypsum panel is classified as Type X in accordance with ASTM Standard C1396 when it achieves a one-hour rating in accordance with ASTM Standard E119 as applied to both sides of 2-inch by 4-inch wood studs spaced 16 inches o.c. (on center), with the long dimension oriented parallel to the studs and attached to the studs with 1-7/8-inch-long, cement-coated nails spaced 7 inches o.c., with the joints treated with paper tape and joint compound.

Non-combustible walls have achieved one-, two-, three- and four-hour ratings employing steel studs and single or multiple layers of gypsum panels. The most basic one-hour wall is listed in Underwriters Laboratories' (UL) Fire Resistance Directory as Design No. U465. It is composed of a single layer of 5/8-inch Type X gypsum panels on both sides of 25 gauge (18 mil) metal studs spaced a maximum of 24 inches o.c.

Most of the gypsum panels covered in this design must be applied vertically and be attached to the studs with 1-inch-long Type S screws spaced 8 inches apart in the perimeter and 12 inches apart in the field of the panels. The use of thermal insulation for sound purposes is optional in this design.

A standard two-hour system is listed in the directory as Design No. U411. This design specifies a double layer of 5/8-inch Type X gypsum panels on both sides of 25 gauge (18 mil) metal studs spaced a maximum of 24 inches o.c. It is interesting to note that finishing of the joints is not required in this specific assembly. Once again, insulation is optional. An alternative to this is UL Design U412, in which the same two-hour rating can be achieved with two layers of 1/2-inch Type C gypsum panels on both sides of the studs in place of the 5/8-inch Type X gypsum panels.

By adding layers of gypsum panels to each side of the studs, the fire resistance of virtually any wall can be increased by one hour. Design No. U435 covers three- and four-hour ratings with three and four layers, respectively, of 1/2-inch Type C or 5/8-inch Type X gypsum panels.

Fire Resistance of Gypsum Panels

When it comes to fire-resistive ratings, the construction industry offers three different types of gypsum panels. Although all gypsum panel manufacturers make different types of panels for a multitude of applications, they all fall into three basic categories: Regular Core, Type X and Type C gypsum panels. The primary difference is in each panel's core composition. Regular core, as the name implies, is a standard or basic core that is non-fire-rated and generally used in a wide range of residential construction applications.

Reviewing the basic chemistry of the product provides a better understanding of the fire resistance of gypsum panels. Gypsum is a naturally occurring mineral and can be found in great abundance around the world. In fact, White Sands, New Mexico, gets its name from the huge gypsum deposit that is located there. Gypsum is a very soft mineral composed of calcium sulfate dehydrate with the chemical composition reflected as CaSO4-2H2O. When gypsum is subjected to heat, 1-1/2 molecules of water are emitted as steam, giving gypsum outstanding fire-resistant properties.

In the early 1950s, comprehensive testing was conducted on gypsum board to confirm that it would achieve the required fire ratings. The testing found that glass fiber strands, when introduced to the core, act as reinforcing bars and increase the product's structural capacity so that the panel can be used in fire-rated construction. Generally, these are known as Type X gypsum panels.

These strands can be exposed by abrading the gypsum core, and they will appear as hairs within the gypsum core. To further enhance the fire performance of the panel, unexpanded vermiculite is added to the core. When it is exposed to fire, the vermiculite will expand and fill the voids created by the departing water. Vermiculite is a natural, non-toxic material that expands with the application of heat, and is frequently used for fireproofing, especially for structural steel and pipes.

To prove the point, some simple comparative tests were conducted. This included taking 13-inch by 12-inch by 5/8-inch-thick samples of Regular, Type X and Type C gypsum panels and installing them in angled horizontal position. A superimposed load of 12 pounds, 9 ounces was applied over each panel. A temperature of 1,800 degrees F was maintained under each one of the samples for the duration of the test. The Regular panel failed only 12 minutes into the test. The Type X gypsum panel failed at 58 minutes, while the Type C panel did not fail during the test (which lasted two hours and two minutes). Upon close examination of the Type C panels, the paper on both the exposed and unexposed sides had disappeared.

UL Design No. U465 5/8" Sheetrock® Brand Firecode® Core Gypsum Panels or Imperial® Brand Firecode Core Abuse-Resistant Gypsum Base, or Fiberock® Brand Panels

UL Design No. U411 5/8" Sheetrock Brand Firecode Core Gypsum Panels, or Fiberock Brand Panels

UL Design No. U435 3/4" Sheetrock Brand Ultracode Core Gypsum Panels

Details Are Important

Details are extremely critical in maintaining the integrity of the system. As noted in the previously cited comparison of gypsum panel types, it is imperative to use the right core formulation for a given application. Type C gypsum panels generally can be used in place of Type X panels, but the opposite is not always true.

If the system calls for a single layer of gypsum panels and the assembly is a floor-ceiling (or roof-ceiling) assembly, it must be a Type C gypsum panel. A Type X gypsum panel likely will not provide the same level of protection. Consequently, it is imperative to specify and install the panel that was used in the test and specified in the individual UL design. UL is an industry-recognized testing laboratory that develops standards and test procedures for materials, components, assemblies and procedures.

Other important criteria include the panel placement and orientation. While it is generally good design practice to stagger the panel joints, it is absolutely imperative to do so in some cases. The intent is not to have a panel joint occur on both sides of the same stud. In addition, if the wall is multilayered, each layer of gypsum should be offset from the layer underneath.

Orientation is the direction in which the gypsum panel is installed relative to the framing. Historically, the panels had to be installed with the long dimension running parallel to the framing (sometimes called installed vertically), as the only data that existed had been developed with this specific panel orientation.

It was not until 1996 that the first successful fire and hose stream tests were conducted on steel stud walls, with the gypsum panels applied perpendicular to the studs (sometimes called installed horizontally), without any backing behind the resulting horizontal joints and without staggering the horizontal joints on opposite sides of the studs.

The primary reason for testing the horizontal application of the gypsum panels was to validate the option of installing the panels horizontally at the top of walls commonly found on commercial construction. Installing them in this manner permits earlier installation of the electrical, plumbing and air conditioning lines, as it is extremely difficult to build fire-rated walls around pre-existing mechanical lines.

The remaining section of the wall is typically finished with the gypsum panels applied parallel to the studs for easier finishing of the joints. The resulting horizontal joint toward the top of the wall (between the horizontally and vertically applied gypsum panels) is typically hidden behind an acoustical ceiling. The pre-installation of horizontally applied panels at the top of the wall is typically referred to as "top down" construction.

The successful test results with the unsupported horizontal joints also eliminated the need to back with framing any horizontal butt joints of vertically applied panels when the specific gypsum panels are used. Furthermore, since the horizontal joints on opposite sides of the studs were not staggered in the fire and hose stream tests, it could be implied that this procedure can be used to build fire-rated walls around previously installed penetrations by splicing the gypsum panels at the height of the penetrants. The resulting horizontal joints on the panels would not need to be staggered. This has been deemed an enormous benefit in retrofit and applications. Again, the specific tested panels must be used in the construction of the walls. The specific orientation of the gypsum panels is noted in the individual UL designs, with the name of the manufacturers and type designation of the panels, as in Design Nos. U419, U420, U423 and U465.

In the Fire Resistance Directory, published by Underwriters Laboratory, (www.ul.com) the Introduction Section, VI. Wall and Partition Assemblies, states the following: "Orientation, vertical or horizontal, of the application of gypsum board in walls and partitions is specified in the individual designs.

Except when gypsum board is allowed to be applied horizontally in the individual wall designs, horizontal butt joints of vertically applied gypsum board should be backed by the same type studs as specified in the design. Alternatively, minimum 25 gauge steel framing with a minimum attachment face of 1-1/4" may be used for the backing. Both edges of the gypsum board forming the horizontal joint shall be attached to the backing with the same screws and spacing as specified in the design for the attachment of the gypsum board edges, then finished as specified for the vertical joints.

Horizontal butt joints on opposite sides of the studs in single-layer applications should be staggered a minimum of 12 inches unless otherwise stated in the individual designs. Horizontal butt joints in adjacent layers on the same face of the assembly in multiple-layer applications should be staggered a minimum of 12 inches unless otherwise stated in the individual designs."

Earlier, several different UL designs were cited as references for the one- through four-hour partitions. Testing has greatly simplified the design and specification of fire-rated walls. As of fall 2006, several designs cover walls with ratings of one to four hours, such as Design Nos. U419 (conventional walls) and U415 (shaft walls).

Another important consideration for designing and maintaining the intended fire rating is to make sure the right fastener and fastener spacing are used.

Steel Stud Drywall Partition Screw Spacing and Location

It should be noted that Underwriters Laboratories provides technical assistance in the interpretation of conditions that are not specifically tested. This assistance is based on the enormous amount of data available to UL on a variety of materials and systems. Many of these situations may have already been reviewed by UL or may have been tested by UL under the so-called "Special Services Investigations."

Examples of these would be the evaluation of corner details that do not specifically fall under the scope of ASTM Standard E119 or the installation of recessed electrical panels in fire-rated walls. Architects and contractors should consult with the manufacturer of the gypsum panels being used in the specific project for assistance regarding special situations.

USG Corporation is a Fortune 500 company with subsidiaries that are market leaders in their key product groups: gypsum wallboard, joint compound and related gypsum products; cement board; gypsum fiber panels; ceiling panels and grid; and building products distribution. www.usg.com

Designing For Fire Resistance with Gypsum Panel Systems
Improving building safety through the use of fire-rated assemblies

The following glossary provides commonly used terms and acronyms pertaining to gypsum panel systems, and the construction and building materials industries.

Alligator Cracks
Fine, random fissures or cracks of the finish plaster surface caused by shrinkage.

Anhydrous Calcium Sulfide
A naturally occurring mineral (CaSO4) usually found in gypsum (CaSO4 2H2O) deposits. Dead-burned hydrite (CaSO4) is generally formed by heating gypsum (to remove all water).

ANSI
A nonprofit, national technical association that publishes standards covering definitions, test methods, recommended practices and specifications of materials.

ASTM
Formerly American Society for Testing and Materials, now ASTM, a nonprofit, national technical society that publishes definitions, standards, test methods, recommended installation practices and specifications for materials.

BCMC
Board for the Coordination of Model Codes; part of the Council of American Building Officials Association (CABO).

BOCA
A nonprofit organization that publishes the National Building Code.

CABO
Council made up of representatives from three model codes. Issues National Research Board (NRB) research reports.

Class A
A fire classification for a product with a flame spread rating of no more than 25 and a smoke developed rating not exceeding 50, when tested in accordance with ASTM E84.

Craze Cracks
Fine, random fissures or cracks of the finish plaster surface caused by plaster shrinkage. These are generally associated with lime finish coat improperly gauged or troweled, or with veneer plasters subjected to rapid-drying job conditions.

Double-Up
Successive plaster coat application with no setting or drying time allowed between coats, usually associated with veneer plastering. The double-up coat is applied (from the same mix) to a scratch coat over gypsum base.

Drywall
Generic term for gypsum panels.

Egg Shelling
Fine cracks in a finish coat similar to craze cracks except that bond is partially destroyed, producing concave fragments of the finish.

Fibered Plaster
Usually a basecoat plaster containing organic or inorganic fibers, which promote cohesiveness in the mix.

Finishing Compound
A compound specifically formulated and manufactured for use over taping or all-purpose compounds to provide a smooth and level surface for the application of decoration.

Fire Endurance
Measure of elapsed time during which an assembly continues to exhibit fire resistance under specified conditions of test and performance. As applied to elements of buildings, it shall be measured by the methods and to the criteria defined in ASTM Methods E119, Fire Tests of Building Construction and Materials; ASTM Methods E152, Fire Tests of Door Assemblies; ASTM Methods E814, Fire Test of Through-Penetration Fire Stops; or ASTM Methods E163, Fire Tests of Window Assemblies.

Fire Resistance
Relative term, used with a numerical rating or modifying adjective to indicate the extent to which a material or structure resists the effect of fire.

Fire-Resistive
Refers to properties or designs to resist effects of any fire to which a material or structure may be expected to be subjected.

Firestop System
A system for protecting against the spread of fire through a penetration in a wall or floor where a pipe or other penetrant passes through a fire-rated system.

Firewall
Fire-resistant partition extending to or through the roof of a building to retard spread of fire.

Flame Spread
Index of the capacity of a material to spread fire under test conditions, as defined by ASTM Standard E84. Materials are rated by comparison with the flame-spread index of red oak flooring assigned a value of 100 and inorganic reinforced cement board assigned a value of 0.

Flammable
Capability of a combustible material to ignite easily, burn intensely or have rapid rate of flame spread.

Flash Set
Premature hardening (setting) of a setting material.

Float
A tool or procedure used to straighten and level the finish coat, to correct surface irregularities produced by other tools, and to impart a distinctive surface texture.

Float Finish
Finish-coat texture that is rougher than a smooth trowel finish, and which is derived from aggregate in the mortar.

Floating Floors
Floors in which a base layer and a top layer are acoustically isolated, either by the use of resilient channels, a resilient membrane, or special isolating spring assemblies.

Gauging
A cementitious material, such as gypsum plaster, Keene's cement or portland cement, added to lime putty to provide and control set; also the act of adding gauging material.

Gypsum
The crystal consisting primarily of Hydrated Calcium Sulfate (CaSO4 2H2O) also known as calcium sulfate dihydrate. Also, a naturally occurring mineral that, when calcined, serves as the base to formulate plastering materials and other building products.

Gypsum Lath
A gypsum board used as the base for application of gypsum plaster.
Gypsum Molding Plaster
A calcined gypsum plaster used primarily for plaster casts or molds, sometimes used as a gauging plaster.

Gypsum Neat Plaster
A calcined gypsum plaster without aggregate; common usage is for gypsum plaster used for basecoats.

Gypsum Partition Tile (Block)
A cast gypsum-building unit of various dimensions for use in non-load bearing interior construction for protection of columns, elevator shafts, etc., against fire.

Gypsum Plaster
Ground calcined gypsum (calcium sulfate hemi-hydrate) combined with various additives to achieve specific application, working and set characteristics. Also the generic name for a family of powdered cementitious products consisting primarily of calcined gypsum with additives to modify physical characteristics, and having the ability, when mixed with water, to produce a plastic mortar or slurry which can be formed to the desired shape by various methods and will subsequently set to a hard, rigid mass.

Gypsum Sheathing
A gypsum board used as a backing for exterior surface materials, manufactured with water-repellent paper and may be manufactured with a water-resistant core.

Head of Wall
A type of construction joint where two fire-rated assemblies intersect. Head-of-wall assemblies occur where a wall intersects a floor/ceiling or roof/ceiling. In these construction details, a fire-protective assembly is needed to protect against the spread of fire. An example is where a partition intersects a fluted steel deck. Head-of-wall and other construction joints are evaluated under UL Standard 2079 for their ability to resist flame and temperature transmission as well as hose stream.

High Calcium Lime
A type of lime containing mainly calcium oxide or hydroxide and not more than 5 percent magnesium oxide or hydroxide.

Honeycomb
A material having cells with a hexagonal, thin-walled cell structure similar to that constructed from beeswax by honeybees to hold honey and larvae.

Hydrate
To chemically combine with water as in the hydration of calcined gypsum or slaking of quicklime. Also the product resulting from this combination.

ICBO
International Conference of Building Officials. A nonprofit organization that publishes the Uniform Building Code.

ICC International Code Committee
A nonprofit organization dedicated to developing a single set of comprehensive and coordinated national model construction codes including the International Building Code (IBC).

Inflammable
Capability of a combustible material to ignite easily, burn intensely or have rapid rate of flame spread.

ISO (International Standards Organization)
A non-governmental network of the national standards institutes of 148 countries, on the basis of one member per country, with a Central Secretariat in Geneva, Switzerland, that coordinates the system.

Key
The grip or mechanical bond of one coat of plaster to another coat, or to a plaster base. It may be accomplished physically by the penetration of wet mortar or crystals into paper fibers, perforations, scoring irregularities, or by the embedment of the lath.

Labeling Service
Program allowing a manufacturer to place Underwriters Laboratories Inc. labels on its products that have met UL requirements. A UL representative visits the manufacturing site to obtain samples of the products for testing by UL. In some cases, samples are also purchased on the open market for testing.

Lamination
Placing a layer of gypsum board over another gypsum board or over another substrate using an adhesive product for attachment. Also, the process of manufacturing products with a thin covering adhered using an adhesive.

Land Plaster
Coarse-ground natural gypsum.

Lath
A metal, wood or gypsum material applied separately to a structure that serves as a base for plaster.

Lay-In Panel
Any panel designed to be supported by an accessible suspension system.

Limiting Height
Maximum height for design and construction of a partition or wall without exceeding the structural capacity or allowable deflection under given design loads.

Model Code
Building code, written and published by a building-official association, available to states, counties, and municipalities for adoption (for a fee) in lieu of their own, e.g., Uniform Building Code, Standard Building Code, National Building Code and International Building Code.

Mortar
A mixture of gypsum plaster or portland cement with fine aggregate or hydrate lime, or both, and water to produce a material with trowelable fluidity.

NBS - National Bureau of Standards
National Bureau of Standards, a federal agency. (Now NIST, National Institute of Technology and Standards).

NCSBCS (National Conference of States on Building Codes and Standards)
National Conference of States on Building Codes and Standards, a nonprofit organization formed to increase interstate cooperation and coordinate intergovernmental reforms of building codes.

NFPA (National Fire Protection Association)
National Fire Protection Association. An international technical society that disseminates fire prevention, fire fighting and fire protection information. NFPA technical standards include the National Electrical Code, and the National Building Code.

Noncombustible
Definition excerpted from the International Code Council (ICC): Material of which no part will ignite and burn when subjected to fire. Also defined as a material with a structural base of noncombustible materials as defined, with a surface not over 1/8" thick that has a flame spread rating of 50 or less. The term does not apply to surface finish materials.

Partition
An interior wall that divides one room from another and is not over one story in height. Partitions may be permanent.

Party Wall
A wall or partition separating two occupancies in a building.

Performance Specification
States how a building element must perform as opposed to describing equipment, products or systems by name.

Perlite
A siliceous volcanic glass that, when expanded by heat, is used as a lightweight aggregate.

Plaster
A cementitious material or combination of cementitious materials and aggregate that, when mixed with water, forms a workable mass. When applied to a surface, plaster adheres to it and subsequently sets or hardens, preserving in a rigid state the form or texture imposed during the period of plasticity.

Plaster Base
Gypsum panel with specially treated face paper to serve as a stable backing for plaster applications.

Plaster Bonder
A material applied to a surface to improve the quality of the bond between it and the succeeding application.

Plaster of Paris
Hemihydrate gypsum or calcium sulfate (CaSO4 " 1¼2 H20) without set control additives, used in casting and industrial applications.

Portland Cement
A hydraulic cement produced by pulverizing portland-cement clinker, consisting primarily of fused hydraulic calcium silicates and usually containing calcium sulfate

Potassium Aluminum Sulfate
Alum; a generally recognized accelerator of gypsum.

Prescription Specification
Traditional procedure used on building projects to describe by name products, equipment or systems to be used.

Retempering
A procedure whereby plaster (usually Keene's cement or portland cement) is remixed to a workable consistency using water and/or mechanical action.

Safing
Firestop material in the space between floor slab and curtain wall in multi-story construction.

Safing Off
Installation of fire safety insulation around floor perimeters, between floor slab and spandrel panels.

Through Penetration Firestop
A system for sealing penetrations in fire-resistant floors, walls and ceilings.

Through Penetrations
An opening through a fire-resistive partition or floor/ceiling assembly caused by the need to have a penetrating item pass through it. Through penetrations usually require the use of a firestop system to protect against the spread of fire through the opening.

Type X
A gypsum board with specially formulated core to increase fire retardant properties and improve system fire-resistance rating.

UBC (Uniform Building Code)
Uniform Building Code. Document promulgated by the International conference of Building Officials.

UL
Program allowing a manufacturer to place Underwriters Laboratories Inc. labels on its products that have met UL requirements. A UL representative visits the manufacturing site to obtain samples of the products for testing by UL. In some cases, samples are also purchased on the open market for testing. The public is thereby assured that products bearing the UL label continually meet UL specifications.

Vermiculite
A micaceous mineral expanded by heat and used as an aggregate.

Warnock Hershey International
WHI. An independent fire-testing laboratory.