Structural Fire Resistance: Standing Up to Fire

CNY Engineering Expo

November 7, 2016Michael J. Klemenz, PE, PMSFPE

Upstate Fire Protection Engineering, PLLC

Agenda

• Background & History of Fire Resistance

• Fire Loads in Buildings

• Building Construction Types

• Code Overview of Structural FRR

• ASTM E-119

• Methods of Fire Resistance

• Fire Resistance of the Future

BACKGROUND & HISTORY OF FIRE RESISTANCE

Fire Resistance Definitions

• Fire Resistance: The measure of the ability of a material, product, or assembly to withstand fire or give protection from it.

• Fire Resistance Rating: The time, in minutes or hours, that materials or assemblies have withstood a standard fire exposure.

• FRR are determined by conducting standardized fire tests or calculations.

Fire Resistance

• Fires can and do occur in buildings• Buildings contain combustible fuels with ΔHc

• Ignition sources present• Fire exposure can be severe & cause failure of

structural assemblies (not a desirable building feature).

Q: Is there such a thing as a “fireproof” building?

Chicago 1967: “Fireproof” Convention Hall

>600 Fatalities

…absolutely fireproof...

Dec. 31, 2015: The Address Downtown Dubai hotel caught fire hours before the New Year's Eve fireworks in Dubai. (Ahmed Jadallah / Reuters)

Fire Resistance Ratings

A: Probably not. Destructive fires are quite possible.Codes may prescribe that the building structure must:• Resist the effects of a fire for a certain

duration• Structure must not contribute to the fuel load• Compartmentation/passive fire protection

systems

Code of Hammurabi (16th Century)

• If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death.

[The first performance-based construction code]

18th & 19th Century

• Fire codes try to prevent conflagrations• Famous conflagrations:

YEAR CITY BUILDINGS LOST

1740/1838 CHARLESTON, SC 300/1158

1835 NEW YORK CITY 674

1845 QUEBEC 1500/1300

1862 TROY, NY 507

1871* CHICAGO, IL 15,000

1973 CHELSEA, MA 1400

2013 WEST, TX 100’s

2013 Lac-Megantic, QC >30

Excerpt from FPH TABLE 1.3.2 Various Notable Citywide Non-warfare Conflagrations in North America

20th Century

• 1918: Standard time temperature curve (“STTC”) fire exposure was adopted by ASTM and others.

20th Century

• 1920’s: NBS (now NIST) performed fire tests in mockups of office & paper records storage to correlate fire load/fire duration.

• Correlated fire endurance to the presumed burnout time of a compartment.

20th Century

• Late 1920’s: NBS conducted full scale tests in vacant buildings in downtown Washington, DC

• Tests of the Severity of Building Fires was written by Simon H. Ingberg, Chief of Fire Resistance Division

• Scientific data regarding fire severity, duration & FR were incorporated into national standards and model building codes

20th Century

• Scientific test methods were developed to provide consistent, objective measurements of fire resistance.

• Eliminated ‘subjective marketing’ of fire resistance performance.

• Like assemblies could be compared.

20th Century

• Ingberg to the Rohm and Haas Company, which was promoting the use of plastics in buildings:

“You should so conduct yourselves that when your products are involved in a disastrous fire, and they certainly will be, that there is nothing in the occurrence for which you must apologize.”

21st Century

• We know today that the STTC is technically obsolete.

• Yet, it still provides good results for most building applications.

• Does not account for todays lightweight structural assemblies or polymer fuels with high HRR.

FIRE LOADS IN BUILDINGS

Fire Load

• Buildings are constructed for a purpose; they are rarely empty.

• Expected fire severity and duration are related to quantity and ΔHc (heat energy/unit mass) of contents.

• Fuel Load- mass of combustibles/unit area• Fire Load- heat energy/unit area of

combustibles

Fire Load

• Ordinary (non-polymer) combustibles have ΔHc ≈ 16.3 MJ/kg (or 8,000 BTU/lb)

• “Fire Load” of various occupancies was estimated by NBS in the 1920’s.

Use Combustible Content (lb/sf)

Clerical 5.8

Lobby 2.6

Conference 4.2

Library 30.2

Storage 11.7

FPH TABLE 18.1.2 Characteristic Fire Loads in Office Buildings

Fire Load

• ΔHc x fuel load ≈ Total theoretical energy released during combustion/unit area.

• Example:

14 ft. x 14 ft. office space; fuel load is 1,098 lb; assume ΔHc = 8,000 BTU/lb. Calculate the Fire Load.

1,098 lb/196 sf = 5.6 lb/sf

8,000 BTU/lb x 5.6 lb/sf = 44,800 BTU/sf

44,800 BTU/sf x 196 sf = 8.78M BTU Total Energy

Fire Load

• NFPA 13 describes hazard classification as “light”, “ordinary” or “high” depending on expected fire severity.

Fire LoadCombustible Content Fire Load (BTU/sf) Fire Duration (Hours)

5 lb/sf 40,000 0.5

10 lb/sf 80,000 1.0

20 lb/sf 160,000 2.0

30 lb/sf 240,000 3.0

40 lb/sf 320,000 4.5

FPH TABLE 18.1.1 Estimated Fire Severity for Offices and Light Commercial Occupancies

Fire Load

• Aforementioned results are very broad & general

• Actual compartment HRR is affected by fire dynamics (combustion air, fuel geometry, burning rates, combustion efficiency, compartment geometry, etc.)

BUILDING CONSTRUCTION TYPES

Common Building Materials

• Steel reinforced concrete, steel, gypsum & wood.

• Each has unique fire resistance characteristics• Each also has cost and constructability

implications.

Common Building Materials

• Steel Reinforced Concrete- Noncombustible; low thermal conductivity; FRR ratings ≥ 4 hours if lightweight and specific aggregates are used.

• Steel- Noncombustible; high thermal conductivity; thermal expansion; yield strength as temperature ; almost always requires protective coating or membrane to delay heat penetration.

Common Building Materials

• Gypsum Board- 21% chemically-bonded water which can vaporize under fire conditions; low thermal conductivity; FRR 20 min. to ≥ 1 hour single layer; low mechanical strength.

• Wood- Combustible; performance varies with dimensions; normally requires protective coatings or membranes to improve FRR; note heavy timber.

Composite Assemblies

Construction Types

• Types I and II- Structural elements are noncombustible; specific FRR for Type I.

• Type III- Noncombustible exterior walls; interior structural elements are any materials permitted by the code.

• Type IV (Heavy Timber)- Noncombustible exterior walls; interior building elements are solid or laminated wood; 6x6, 6x8, 6x10

Construction Types

Construction Types:

• Type V- structural elements, exterior walls and interior walls are of any materials permitted by the code.

Type I Construction

Type I Construction

Type II Construction

Type II Construction

Type III Construction

Type IV HT Construction

Type V Construction

Type V Construction

CODE OVERVIEW OF STRUCTURAL FRR

Building Code

• Required FRR are tied to building use, floor area and building height

• FRR are be determined by ASTM E119 or in accordance with Section 703.3.

• Penetration of FRR assemblies require special attention.

Building Code

• Chapter 5: Height & fire area constraints based on construction type & use group.

– Note that Height/fire area may be increased for fire sprinklers

• Chapter 6: Defines FRR of structural elements for the various construction types

Building Code

Building Code

Building Code

HT = 8x8 for columns supporting floors, 6x8 supporting roof or ceiling; 6x10 for beams supporting floors

Building Code

Chapter 7

• 703: Fire-resistance Ratings And Fire Tests

• 704: Fire-resistance Rating Of Structural Members

• 705: Exterior Walls

• 706: Fire Walls

• 707: Fire Barriers

• 708: Fire Partitions

• 711: Floor And Roof Assemblies

Building Code

703.3 Methods for determining FR:• Fire-resistance designs documented in approved sources.• Prescriptive designs of fire-resistance-rated building

elements, components or assemblies as prescribed in Section 721.

• Calculations in accordance with Section 722.• Engineering analysis based on a comparison of building

element, component or assemblies designs having fire-resistance ratings as determined by the test procedures set forth in ASTM E119 or UL 263.

• Alternative protection methods as allowed by Section 104.11.

• Fire-resistance designs certified by an approved agency.

TEST METHODS

UL 253/ASTM E-119

• Standard Test Methods for Fire Tests of Building Construction and Materials

• Tests walls & partitions, floor & roof assemblies, columns, beams, etc.

• Full scale (partial) assembly is constructed in test furnace; fire exposure from one side; restrained or unrestrained.

• Fire exposure follows the STTC

UL 253/ASTM E-119

UL 253/ASTM E-119

• Furnace temperature and pressure are precisely controlled.

• Specimen must meet certain parameters to receive a FRR:– Must sustain load– Must not allow flame passage– Unexposed side < 250°F (140°C) above the

assembly’s initial temperature.– No passage of water during hose stream test

METHODS OF FIRE RESISTANCE

Methods of Fire Resistance

• Sufficiently massive structural members• Encasement (concrete, water)• Protective coatings (concrete/gypsum-based)• Membrane/board protection (GWB)• Intumescent coatings• Composite assemblies (floor/ceiling, etc.)

Concrete Encasement

Spray-applied coating

Membrane/Board

US Steel Tower, Pittsburgh, PA

Intumescent Coating

Harmathy’s “Ten Rules of Fire Endurance Ratings” [May 1965 Edition of Fire Technology]

• Rule 1: The "thermal” fire endurance of a construction consisting of a number of parallel layers is greater than the sum of the "thermal" fire endurance’s characteristic of the individual layers when exposed separately to fire.

• Rule 2: The fire endurance of a construction does not decrease with the addition of further layers.

• Rule 3: The fire endurance of constructions containing continuous air gaps or cavities is greater than the fire endurance of similar constructions of the same weight, but containing no air gaps or cavities

Harmathy Cont’d

• Rule 4: The farther an air gap or cavity is located from the exposed surface, the more beneficial is its effect on the fire endurance.

• Rule 5: Increasing the thickness of a completely enclosed air layer cannot increase the fire endurance of a construction.

• Rule 6: Layers of materials of low thermal conductivity are better utilized on that side of the construction on which fire is more likely to happen.

Harmathy Cont’d

• Rule 7: The fire endurance of asymmetrical constructions depends on the direction of heat flow.

• Rule 8: The presence of moisture, if it does not result in explosive spalling, increases the fire endurance.

• Rule 9: Load-supporting elements, such as beams, girders and joists, yield higher fire endurance’s when subjected to fire endurance tests as parts of floor , roof, or ceiling assemblies than they would when tested separately.

• Rule 10: The load-supporting elements (beams, girders, joists, etc.) of a floor, roof, or ceiling assembly can be replaced by such other load-supporting elements which, when tested separately, yielded fire endurance’s not less than that of the assembly.

FIRE RESISTANCE OF THE FUTURE

Tall Timber Buildings

• AKA Mass Timber Buildings

• More sustainable building materials

• Accounts for charring characteristics of large wood members

• Limited research and testing in US

• CFD methods and calculations have concluded acceptable performance of wood structure; comparable to steel/concrete

Other Fire Curves

Updates to UL 263 & 1709

1. Load restriction factors for steel beams need not be applied to any UL Design that is based upon strength calculated using the 2005 or 2010 AISC Specification.

2. Load restriction factors for steel beams need not be applied to any other UL Design if an unrestrained beam rating is used.

3. Load restriction factors for steel beams need not be applied to any other UL Design if a 1-hour restrained beam rating is used.

4. When using a UL Design for which none of the foregoing conditions applies, a load restriction factor of 0.9 is applicable for both composite design and non-composite design in U.S. practice.

Other Methods

• Performance-based design• Fire resistant steel alloys• Sprinkler and Water Mist Systems• Aerogels- silica materials with nano-meter

scale pores “puffed up” to 99% open porosity. When exposed to heat it does not thermally degrade

• Ablative Coatings• Subliming Compounds

Q&A

Q&A

Q1: Is there such a thing as a fireproof building?

A1: Depends on what you mean by “fireproof”. But most likely, “NO”.

Q&A

Q2: Is steel a more fire-resistant building material than wood?

A2: Depends. Steel loses 50% of its yield strength at 1100O F (590O C). Large wood members tend to char and insulate remaining wood from further pyrolysis.

Q&A

Q3: Is fuel load (fire load) the sole indicator of fire severity?

A3: No. Other factors include air available for combustion, fuel geometry, combustion efficiency, compartment geometry, etc.

Q&A

Q4: True or False: Fire resistance is simply a measure of whether an assembly will resist extreme temperatures?

A4: False. Assembly must also maintain its integrity and continue to support design load.

YOUR QUESTIONS?

References

1. NFPA 251, Standard Methods of Tests of Fire Resistance of Building Construction and Materials

2. 2016 Building Code of New York State (2015 IBC), including the 2016 Uniform Code Supplement

3. NFPA Fire Protection Handbook, 20th Edition

4. Test of the Severity of Building Fires, David Evans, Daniel Gross, and Richard Wright

5. Fire Protection of Structural Steel in High-Rise Buildings

6. Ten Rules of Fire Endurance Ratings by T.Z. Harmathy in the May 1965 Edition of Fire Technology (35)

7. 120 Years Of Structural Fire Testing: Moving Away From The Status Quo, Cristián Maluk and Luke Bisby, The BRE Centre for Fire Safety Engineering, The University of Edinburgh

Structural Fire Resistance: Standing Up to Fire

CNY Engineering Expo

November 7, 2016Michael J. Klemenz, PE, PMSFPE

Upstate Fire Protection Engineering, PLLC