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Ch 07 Heavy Timber and Mill Construction
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Ch 07 Heavy Timber and Mill Construction

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  • 1. 7 Heavy Timber and Mill Construction
  • 2. Objectives (1 of 2)
    • Identify and describe the similarities and differences between mill and heavy timber (Type IV construction)
    • Identify the dimensions of heavy timber members
    • Describe why the misnomer “slow burning” is inappropriate for heavy timber buildings
    7
  • 3. Objectives (2 of 2)
    • Identify the hazards of conflagration breeders
    • Describe the hazards of vacant heavy timber buildings and structures under demolition
    • Identify new structures that incorporate heavy timber construction
    7
  • 4. A History of Mill and Heavy Timber Construction
    • Heavy timber construction descendent of true mill construction
    • Developed in New England
    • Building design that eliminated serious faults of mill construction
    7
  • 5. Mill Features (1 of 3)
    • Exterior bearing and nonbearing walls are masonry
    • Columns and beams are of heavy timber with cast iron connectors
    • Floors are of thick grooved, splined, or laminated planks
    7
  • 6. Mill Features (2 of 3)
    • Roofs supported by beams or timber arches and trusses
    • Adequate fire barriers
    • Ends of girders are fire cut
    • Cast iron box
    • Corbelled beams
    • Scuppers
    7
  • 7. Mill Features (3 of 3)
    • Concealed spaces are eliminated
    • Vertical openings are protected
    • Automatic sprinkler system
    • Special hazards put in detached buildings
    7
  • 8. Conversion, Modification, and Preservation (1 of 2)
    • Remodeling
      • Often detracts from the original fire characteristics
      • Columns may have been removed
      • New trusses do not have the inherent resistance of the old columns and beams
    7
  • 9. Conversion, Modification, and Preservation (2 of 2)
    • Changes in Use
      • Conversions to tenant factories, storage, discount stores, and apartments
      • Fire loads are often beyond capacity of the installed sprinklers
      • Unsprinklered areas are created
    7
  • 10. Heavy Timber Building
    • Requires careful maintenance
    • Deficiencies should be clearly noted
    • Realistic prefire scenarios are required
    7
  • 11. Code-Classified Heavy Timber Construction
    • Type IV construction
    • Often lacks at least one feature vital for fire safety
      • Unprotected steel columns, part-steel trusses, unsprinklered void spaces, or no sprinkler protection
    7
  • 12. Heavy Timber Construction Contractors
    • Be wary of those who claim to be erecting a heavy timber structure
    • Many do not know the actual dimensions required
    7
  • 13. Heavy Timber Theory
    • Heavy timbers are difficult to ignite
    • Will char on the surface only
    • Over the years the floors may have been soaked with flammable and combustible fluids
    7
  • 14. Slow Burning?
    • Proponents of heavy timber construction
      • Believe “slow burning” means “collapse resistance”
      • Statement true only if fire department can maintain interior offensive operations
    7
  • 15. Definition of Conflagration Breeder
    • A structure that presents severe exposure problems that are capable of initiating a large, multiple building fire which is not easily contained
    7
  • 16. Characteristics of a Conflagration Breeder 
    • Radiant heat and fire brands
    • Large collapse zones
    • Fire spread
    • Shut-off sprinkler systems, open equipment shafts, and uncompartmented areas
    7
  • 17. Fighting a Conflagration Breeder
    • Expect the fight of your life
    • You need:
      • Large water supply
      • Numerous heavy caliber streams
      • Large collapse zone
      • Extensive brand patrol downwind
        • Luck
    7
  • 18. Use of Unprotected Steel
    • Unprotected steel can fail early and trap fire fighters
    • Alteration permits give clues to real composition
    7
  • 19. Beams
    • Penetrated for conduits or pipes
    • Long bolts and nuts are used
    • Metal can provide a path for heat to reach the interior
    • Watch for spliced timbers with overlapping joints and metal connectors
    7
  • 20. Full Sprinkler Protection
    • Needs to be adequately maintained
    • Only fire protection measure to prevent a disaster in a heavy timber building
    7
  • 21. Rehabilitation and Demolition Hazard
    • Fire sprinkler systems
      • Must be adequately maintained
      • Expense may be seen as road block to construction project
    7
  • 22. Problems with Rehabilitation
    • Abandoned buildings
    • Conversions to multiple occupancy
    • Rehabilitations into apartment or office occupancies
    7
  • 23. Vacant Buildings
    • Cities with recent massive downtown fires
      • Baltimore
      • Philadelphia
      • Lynn (Massachusetts)
      • Minneapolis
      • Indianapolis
      • Montreal
    7
  • 24. Characteristics of Massive Downtown Fires
    • Old combustible interior masonry buildings
    • Fire barriers removed or inoperable
    • Sprinkler systems removed or disabled
    • Only fuel was the interior structure of the building
    7
  • 25. Vacant Structures
    • Sprinklers are often turned off
    • Open invitation to arson
    7
  • 26. Modern Heavy Timber Buildings
    • Not being built in record numbers
    • A niche for certain types of occupancies
    • Most common use is the modern heavy timber church
    7
  • 27. Summary
    • Heavy timber construction is a descendent of true mill construction
    • Remodeling has detracted from original fire characteristics
    • Proponents often advance the term slow burning
    • Full sprinkler protection is the only adequate fire protection measure
    7