Ch 07 Heavy Timber and Mill Construction

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