9 Noncombustible

Construction

Objectives (1 of 2)

• Understand the difference between noncombustible and fire-resistive construction

• Identify the different types of steel building components and their characteristics

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Objectives (2 of 2)

• Describe different types of steel structural systems

• Describe the hazards of a metal deck roof fire

• Understand the hazards of high fire loads in unprotected steel structures and ways to improve the situation

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Introduction• Noncombustible and fire resistive

construction

• Differ in the level of fire resistance assigned to the structural frame, walls, floors, and roof

• Noncombustible construction has little fire resistance

• Fire resistive construction has moderate to heavy fire resistance

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Noncombustible Construction

• Allowable area and height is much less than fire resistive construction

• Maximum height is 12 stories

• Fire resistive can have unlimited height

• Fire-resistive construction can use steel for its framing system

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Steel

• Modulus of elasticity about 29 million pounds per square inch (psi)

• High tensile strength and shear strength

• Strong but lightweight members have little inherent fire resistance

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Fire Characteristics of Steel

• Substantial elongation

• Above 1300°F, steel members may fail

• Cold-drawn steel will fail at about 800°F

• Steel transmits heat readily

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Unwarranted Assumptions

• False belief in steel’s “fireproofness”

• Need to set priorities

• Heat absorbed by contents or structural elements is the most important heat

• Heat being evolved from contents that are burning is of secondary importance

• Heat leaving the structure—let it go

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Water on Hot Steel

• Water is the fire department’s heat removal medium

• Myth: Water should not be thrown on heated steel

• Cooling effect of water draws steel back to its original dimensions

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Definitions: Steel Construction Members (1 of 3)

• Angles

• Bars

• Box columns

• Box girders

• Channels

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Definitions: Steel Construction Members (2 of 3)

• I-beams

• Plates

• Purlins

• Rolled or built-up members

• Spandrel girders

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Definitions: Steel Construction Members (3 of 3)

• Tees

• Tubes

• Weight

• Wide-flange shapes

• Zees

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Steel as a Construction Material (1 of 2)

• Makes it possible to erect tall buildings

• Has consistency in structural characteristics

• Can be connected to other structural elements

• Used for fire escapes

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Steel as a Construction Material (2 of 2)

• Provides the tensile strength that concrete lacks

• Used in concrete flooring systems

• Used to repair failures in concrete buildings

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Steel Buildings

• Used in peaked roofs

• Bar joists span the main trusses to support a flat roof

• Steel is almost universally unprotected.

• Buildings often can only be classified as noncombustible

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Protected Noncombustible Sprinklered Construction

• Found occasionally

• Major structural elements have fire resistance

• Building itself is not fire resistive

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Rigid Frames

• Column is narrow at the base and tapers to its widest point at the top

• Girder is also tapered

• Wide haunch resists the outward thrust of the roof

• Clear spans of about 100 feet

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Steel-Framed Buildings

• Many are prefabricated

• Butler Company is a prominent manufacturer

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Huge Spans

• Span collapses can be sudden and tragic

• Adjacent bents are tied together

• Tying the steel units together creates dependencies between torsional or eccentric loads

• The higher the resistance to wind load, the more likely a progressive collapse

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Developing Wide-Span Trusses

• Designs may push the limits of steel

• Hasty field changes or errors in construction can have catastrophic consequences

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Deep Parallel-Chord Trusses

• Floor beams in hospitals

• Interstitial space

• Such voids should not be used for storage or maintenance

• Automatic sprinklers should be required

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Heavy Parallel-Chord Trusses

• Have been used as transfer beams

• Often hidden in partition walls

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Trussed Arches

• Arch of a steel arch bridge is often a truss

• Is a compression structure

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Walls of Steel-Framed Buildings

• Wall composition varies

• Metals, cement-asbestos board, masonry, concrete, and reinforced plastics found

• Wall insulation and coatings also factors

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Cement-Asbestos Board

• Noncombustible and is often used for friable construction

• Friable construction is used where an explosion is a possibility

• Will break away readily and relieve pressure

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Glass-Fiber Reinforced Plastics

• Noncombustible

• Resinous binder most often used with it is flammable

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Aluminum

• Noncombustible, but has a low melting point

• Has little mass per unit of area, so it disintegrates rapidly in a fire

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Precast Prestressed Concrete Panels

• Usually erected in large sections

• Collapse is hazardous to fire fighters

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Masonry Walls

• Often used for walls for unprotected steel-framed buildings

• Made of concrete block or a composite

• Usually only curtain walls

• Important to analyze the effect of the expansion of the steel frame on the wall

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Galvanized Steel Walls

• Used when heat conservation is not important

• Asphalt asbestos protected metal (AAPM)

• Robertson Protected Metal (RPM) is one proprietary name

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Metal Panels

• Prefabricated metal panels in a sandwich construction

• Plastics are often used with metal panels

• Insulation, vapor seal, or adhesive in the panels may be combustible

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Polyurethane Insulating Panels

• Protected by gypsum board and stainless-steel sheathing

• If a cutting torch is later used, a smoky, destructive fire may result

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Aluminum Sandwich Panels

• Can be made with foamed polyurethane

• Some are listed by Underwriters Laboratories (UL) Inc. for low flame spread ratings

• Smoke-developed ratings may be quite high

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Failure of the Closure of the Wall Panel to the Floor Slab

• Design of panel walls

• Method of installation

• Degradation of insulation

• Expansion of metal under fire conditions

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High-Rise Framing

• Steel once stood unchallenged as a method for high-rise buildings

• Concrete now is finding more use

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Builders’ Hesitation

• Brick, stone, and terra cotta added to framed buildings

• Goal was to reduce the apparent or perceived height of the building

• Didn’t openly discuss use of steel-frames

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Tilt-Slab Hazards

• Walls braced with tormentors or braces until the roof secured

• If the roof is being lost in the fire, beware of wall collapse

• If heavy smoke is present, the sprinklers are not controlling the fire

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Steel-Framed Buildings Under Construction

• Wind forces must be resisted, because the building is not fully connected

• Braces may not be properly installed

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Plastic Design in Steel Construction

• Connections are built to transfer loads beyond the column

• Beams are lighter and columns are smaller than they would be otherwise

• The lighter the steel, the less fire resistance

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More on the Fire Characteristics of Steel

• Conducts heat

• Elongates as temperature increases

• Loses strength at high temperatures

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Steel Conducts Heat

• Steel transmits heat

• Tin ceilings can transmit fire

• The conductivity of steel can be a factor in spreading fires

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Ships

• Practice of using ships as buildings is growing

• Ships have steel walls known as bulkheads

• Welding operations are performed without concern for heat transmission

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Self-Storage Facilities

• Have many of the characteristics of ships

• Fire can spread from unit to unit by conduction and radiation

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Steel Elongates

• Expands from 0.06 percent to 0.07 percent for each 100°F rise

• At 1000°F, a steel member will expand 9 1/2 inches over 100 feet of length

• Above 1000°F, steel starts to soften and fail

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Elongating Steel

• Exerts a lateral force against the structure that restrains it

• Expansion of steel may cause the displacement of masonry

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Hot, Fast Fires Effect on Steel Buildings

• Failure temperatures are reached rapidly

• Lateral thrust against the wall is minimized

• Overturning can be anticipated

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Steel Fails• Steel above 1000°F starts to lose strength

rapidly

• National Fire Protection Association (NFPA) 251 (American Society of Testing and Materials (ASTM) E119) test reaches 1000°F in five minutes

• National Institute of Standards and Technology (NIST) test reaches 1500°F in five minutes

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Standard Tests of the Fireproofing of Steel Columns

• Test ends when a temperature of 1200°F is exceeded at one point or 1000°F is exceeded on the average in the column

• A principle variable is the weight or mass of the steel unit

• Ventilation is also a factor

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Overcoming the Negative Fire (1 of 2)

• Ignore the problem

• Rely on an inadequate code

• Take a calculated risk

• Fireproof (insulate) the steel

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Overcoming the Negative Fire (2 of 2)

• Protect the steel with sprinklers

• Fireproof the steel with a water cooling system

• Locate the steel out of range of the fire

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Ignoring the Problem

• Potential for fire damage to steel buildings is not clearly understood

• Unwarranted confidence on the fact that the steel is noncombustible

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Steel Highway Structures and Bridges

• Unprotected steel that is vulnerable to an occasional gasoline truck fire

• New York City Fire Department has had preplans in place for the East River bridges for over 70 years

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Hazards of Concentrated Fire Loads (1 of 2)

• Unprotected steel buildings may have highly concentrated fire loads

• “One-high story” buildings with internal structures

• Mezzanines, sometimes built of wood

• Other combustible spaces

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Hazards of Concentrated Fire Loads (2 of 2)

• Metal trailers are hazardous, especially when grouped

• Prefabricated buildings, especially with certain types of insulation in walls

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Excavation Bracing

• Building excavations are being made much deeper

• Walers and rakers

• An excavation is loaded with combustibles

• Tiebacks 

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Buildings Under Construction

• Steel may be unprotected for extended periods

• World Trade Center used ordinary plywood to save $1 million

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Relying on Inadequate Codes

• Building Codes

• Unprotected noncombustible or protected noncombustible

• “Protection” refers to physical protection of the steel with gypsum board, spray-on fireproofing, or the like

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Study the Type of Construction

• Column, girder, and beam construction is common

• If a masonry bearing wall is substituted for some of the exterior columns, the building is wall-bearing

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Assumption About Fires

• They burn only upwards

• Example: A fire involving a wooden balcony or a metal deck roof could well cause steel framing to move and thus cause brick-veneered walls to fall

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Steel High Above the Floor

• Codes vary in terms of protection of steel buildings

• Heights 20-30 feet above the floor are often left unprotected as risks are thought to be low

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The McCormick Place Fire

• The main exhibit area provided a clear area of 320,000 square feet

• The columns were trusses themselves.

• The columns were fire protected up to a height of 20 feet

• The roof trusses were unprotected

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What Could Have Been Done Better

• Modern building codes would have required automatic sprinkler system

• Sprinklers could have limited the spread of this fire

• Codes were inadequate

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The New McCormick Place

• Structural steel is protected with directly applied fireproofing delivering one-hour fire resistance

• The entire building is sprinklered

• Provisions have been made for smoke venting

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Important Test Experiences

• Underwriters Laboratories tested in the aftermath of the fire

• Tests done in building 30 feet high with typical fuels

• The first test fires had 1500°F after 5 minutes and 45 seconds

• A bar joist reached 1540°F and an I-beam 1355°F in just over 5 minutes

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Taking Calculated Risks

• Financial Calculation

• Engineering Calculation

• “Forgetting It” Calculation

• Steel Industry

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Insulated Metal Deck Roof Fire Problems

• Fire in the General Motors transmission plant at Livonia, Michigan

• The metal deck roof was the principal contributing factor to the destruction of the plant.

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Insulation

• Is useless when it absorbs moisture

• Must be protected from capillary attraction

• A bituminous coating serves as the adhesive and sometimes as a moisture-stopping vapor barrier

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An Approved Roof

• Is one that meets UL standards

• Can be UL listed but still be a combustible metal deck roof

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When a Fire Occurs

• The metal deck heats up

• Heat is conducted through the deck to the bituminous adhesive

• Adhesive liquefies and then vaporizes.

• When the gas mixes with the air below, it ignites from the fire below

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Prevention of Metal Deck Roof Fires

• Use Factory Mutual Class I roofing or a UL Classified Roof

• Provide adequate automatic sprinkler protection for the roof, even though the contents may be noncombustible

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Fires of Interest (1 of 2)

• Tinker Air Force Base

• A fire was started by roofers

• The sprinklers were below a wire lath and plaster ceiling

• The water did not hit the underside of the roof deck, and the fire burned unimpeded

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Fires of Interest (2 of 2)

• Wabush Mines

• A fire in a large building damaged a metal deck roof 90 feet above the floor

• Even if the roof had been Class I, damage would have been severe

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Class I

• Some think it means “completely satisfactory under all circumstances”

• A Class I roof with any combustibles should not be used over a high-value installation

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Atomic Energy Commission (AEC)

• Studied fire protection for thousands of acres of metal deck roofs

• Decided to add sprinklers to government plants

• Over $20 million was spent on sprinklers and water supplies

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An Unrecognized Problem (1 of 2)

• Metal deck roof a factor in many losses

• Common characteristics of metal-deck roof fires

• Small openings allow rapid fire spread

• Thick, black, choking smoke, sometimes with dripping tar

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An Unrecognized Problem (2 of 2)

• Fire suppression group may not understand the significance of these fires; building codes often are inadequate

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Fighting the Metal Deck Roof Fire

• Marine Corps Supply Depot in Norfolk, Virginia

• Marine plywood office

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Metal Decks on Nonmetal Buildings

• Metal decks found on steel-framed buildings as well as masonry buildings

• Kensington, MD Fire

• In December 1970, a fire broke out in a janitor supply business

• Chief identified as probable metal-deck roof fire

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Types of Protection of Steel Structures

• Unprotected

• Dynamic protection

• Passive protection

• Passive/dynamic combination

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Unprotected Steel

• Has potential for early collapse

• Wichita, Kansas automobile showroom fire

• Repair bays built of lightweight steel truss construction

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Need to Cool All Heated Steel

• The quantity of water is not excessive

• Cool all the steel that is within reach of hose streams and give special attention to columns

• Solid stream tip might be better than a fog tip

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Water Damage

• Some argue against the use of water because of the damage it can cause

• If owners had sprinklered the building, water would be discharged anyway

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Dynamic Fire Protection

• Accomplished with various types of automatic sprinkler systems

• Hydraulically calculated sprinkler design is no guarantee of success

• Heavy structural steel sometimes is protected by special lines of sprinklers.

• Deluge and fog/foam systems used for flammable liquids

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Passive Fire Protection (1 of 2)

• Is the legally required level of fire resistance adequate for the fire load as it exists in the building?

• Has the protection of steel been provided, and is it maintained?

• Is there any legal relief?

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Passive Fire Protection (2 of 2)

• Is it up to the fire department simply to do the best it can in the event of a fire?

• If the fire department estimate of the situation indicates potential or inevitable disaster, who, if anyone, is notified?

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What All Personnel Should Know

• The requirements for fire resistance as applied to specific buildings

• The manner in which fire protection can be degraded is also crucial

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Degradable Methods

• Sprayed-on protection

• Membrane fireproofing

• Fire-rated tile

• Considerations

• Permitted under local code?

• Could tampering have occurred which might make less effective?

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Passive/Dynamic Protection

• Partial static protection (such as a spray-on coating) used along with automatic sprinklers

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Code Problems• Develop competence

• One person or group should become familiar with current and past local building codes

• Building officials may be less than enthusiastic about fire fighter involvement.

• Some fire prevention managers are equally unenthusiastic about fire fighter involvement

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Code Variances

• Code exceptions might be made by building and fire prevention officials

• Codes do not permit waivers to specific requirements

• All modifications to requirements of the code should be fully documented

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Preplanning Your “McCormick Place”

• Make your own case study

• Consider a possible preplan of a fire in an unprotected steel building being used as an exhibit hall

• Assume there is a balcony running down both sides that is used for sports events but not for exhibits

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First Moves in a Case Study

• Battle for sprinkler protection or denial of the facility to high fire-load exhibits

• After you lose, get in writing an agreement that the fire department can take whatever steps necessary to protect life and property during exhibits

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Consider a Worst Case Scenario (1 of 2)

• An exhibition with a potential for a high rate of heat release in a fire

• A hot, fast fire is anticipated indicates a more severe test of the structure than a slower fire

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Consider a Worst Case Scenario (2 of 2)

• Do you need an alternative automatic system?

• Study the potential water supply and needs

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Be Proactive

• Watch for new ideas

• Step-by-step logic leads to the practical solution

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Summary (1 of 2)

• Steel is the most important metal used in building construction

• Steel has several important characteristics to consider regarding its behavior in fire.

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Summary (2 of 2)

• Steel structures can be divided into the following types:

• Unprotected

• Dynamically protected

• Passively protected

• Passive/dynamic combination protection

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