Maryland Fire&Rescue



Title: Hazards to Firefighters of Engineered Wood Products

Time: 2 – 3 hours

Teaching Materials:

• Computer

• Projector or Television

• PowerPoint® Presentation

References:

structural-composite/lumber

articles/2007/04/silent-floors-silent-killers

articles/print/volume-167/issue-1/features/modern-woodframe-construction-firefighting-problems

niosh/fire/reports/face/200707.html

articles/print/volume-4/issue-2/firefighting-operatios/the-dangers-of-lightweight-construction

news-and-research/publications/nfpa-journal/2009/July-August-2009/features/lightweight-construction



Motivation: There’s a revolution taking place in the building industry and it directly impacts safety and tactics on the fire ground. It’s officially called engineered wood products by the trade industry and they can prove to be deadly to emergency service personnel. Slide #2

Student Performance Objective: The student will be able to identify the various types of engineered wood products, where they are used, the advantages and disadvantages of each and the implications to firefighter safety.

Enabling Objectives:

• The student will be able to identify different types of engineered wood products

• The student will become more familiar with industry terminology

• The student will be able to understand different styles of building systems

• The student will be able to evaluate personnel safety

• The student will be able to determine when a defensive attack is the best option

Overview:

• Terminology

• Uses in Building Construction

• Safety Concerns

• Tactics

I. Brief History of Engineered Wood

A. Developed in the 1970’s

B. Use greatly increased during the housing boom of the 1980’s

C. Driven by dwindling supply of saw-length timber for conventional framing

D. Touted as environmentally friendly because it uses wood that

is of little value or went to waste historically

II. Types of Engineered Wood Products

A. Laminated Veneer Lumber (LVL) Slide #4

1. Produced by laminating thin layers of veneer together

2. Grain of all veneers is parallel to the long direction

3. Dimensionally stable with high strength

4. Virtually free of splitting or warping

5. Because of scarfed or lapped joints, longer spans than with conventional solid wood beams are possible

6. Dimensions can be varied to suit the end-user and

Architectural/engineering requirements

B. Parallel Strand Lumber (PSL) Slide #5

1. Produced by laminating layers of veneer that has been clipped into long strands together

2. Grain of all veneers is parallel to the long direction

3. Fused under pressure and heat with moisture-resistant adhesives

4. Dimensions can be varied to suit the end-user and

Architectural/engineering requirements

5. Dimensionally stable with high bending strength

6. Virtually free of splitting or warping

7. Longer spans possible than with conventional solid wood

beams

8. Used for beams, headers and load-bearing columns

C. Laminated Strand Lumber (LSL) Slide #6 & 7

1. Similar to PSL, but utilizes flaked strands instead of long clipped strands

2. Not as dimensionally strong as LVL or PSL

3. Pressed into a large mat or billet, then sawn into useable sizes

4. Virtually free of splitting and warping

5. Used for studs and millwork components

D. Oriented Strand Board (OSB) Slide #8

1. Flakes of wood pressed together with adhesive to form a sheet

2. Used for flooring, decking and sheathing

1. Oriented Strand Lumber (OSL) Very similar to LSL

2. Basically OSB board made into lumber

3. Used for studs and millwork components

NOTE: LSL and OSL can be produced utilizing sawmill scraps while whole logs are required for LVL and PSL to produce the veneers.

VIDEO – How it’s made LP Building Products Demo Slide #9

A. Glulam Slide #10

1. Lamination of layers of solid wood glued together to make a larger component. Hence: GLUeLAMination

2. Makes a heavy beam similar to the old heavy beam construction, but can be made from small dimensional components.

3. Does not degrade at the same speed as A – E above due to the larger size of the initial components

B. Plywood

1. Lamination of wood veneer to produce a sheet generally 4 feet by 8 feet or 4 foot by 12 feet

2. Used for flooring, decking and sheathing

III. Use of Structural-Composite Lumber in the Construction Industry

A. Floor Joists Slides #11 - 14

1. Traditionally, solid lumber ranging from 2 x 6 up to 2 x 12 inch softwoods (spruce, pine, fir or SPF designation)

2. Composite I-beams or LVL, LSL now more widespread

3. Composite I-beams now account for over 44% of flooring in new residential construction.

B. Beams and Headers

4. Traditionally, solid lumber ranging from 2 x 6 up to 2 x 12 inch softwoods (spruce, pine, fir or SPF designation)

5. Composite I-beams or LVL, LSL now more widespread

C. Roof Trusses Slide #15

1. Standard was 2 x 4 or 2 x 6 engineered utilizing metal gusset plates

2. Now beginning to see engineered wood being substituted for the solid materials

D. Wall Framing Slide #16

1. Traditionally, solid dimensional lumber of 2 x 4 or 2 x 6 inch softwoods (spruce, pine, fir or SPF designation)

2. Newer construction utilizing framing made of LSL

E. Columns

1. Usually solid lumber

2. Now seeing PSL material being substituted

F. Roof Decking, Flooring and Sheathing Slide #17

1. OSB is used today about 75% of the time, overtaking plywood as the material of choice

IV. Larger Construction Slides #18 – 22

V. Implications for the Firefighter Slide #23

A. Modern construction techniques expose more combustible material to the fire.

1. Softer woods burn faster and more intensely than hardwoods

2. Open trusses and I-beams provide many voids for the fire to spread quickly through the entire floor or ceiling space

3. More surface area is exposed to fire

4. Oxygen is readily drawn in through ample soffit vents and vented through ridge vents. This change was required by Code changes in the 1980’s

5. Exterior siding easily melts away and exposed vertical sheathing to the heat

B. Underwriters Laboratories (UL) conducted tests on engineered wood products (Structural Stability of Engineered Lumber in Fire Conditions) and issued a 100-page report Slide #24

C. Summary of findings:

1. Deflection Times:

Although a computer model predicted that the test floor assembly using engineered I-joists would retain its strength longer during a fire than the traditional wood platform, the opposite was the case. Furthermore, the engineered wood supports began to fail and deflect almost from the start of the test and proceeded to degrade in stages, leading to floor vibration, noise, collapse, and burn-through.

2. Charring:

The rate at which engineered wood and traditional wood chars is similar. However, because of the very thin cross section of the I-beams, the report found that this charring rate poses immediate dangers to the mechanical integrity of the structure.

3. Heat Sensitivity:

Oriented strand board beam sections exhibited initial charring at a much lower temperature than traditional wood, making it impossible to further test some properties of the material.

4. Heat Conduction:

Due to compressed plies and binding material, the engineered samples conducted heat faster than other wood samples.

5. Brittleness:

Engineered wood product samples exhibited increased brittleness and loss of mechanical strength compared with traditional wood components when heated in an oven, even without being exposed to fire. Researchers suggested this was due to separation of the constituent compressed fibers under mechanical and heat stress.

D. Early failure of structural members

1. Engineered products lack mass and have greater surface area

2. Wooden I-beams can fail in just over 6 minutes Slide #26 & 27

3. Wooden floor trusses can fail in just under 14 minutes

4. Time to failure is 35 – 60% shorter than solid wood counterpart

5. Metal gusset plates have a tooth depth of as little as 1/3 of an inch! Therefore, once they begin to deform from heat, they may pull free of the wood, causing failure of the unit.

Slide #28 & 29

6. OSB or plywood fail at about the same rate

7. Neither will support a large load once the truss or I-beam fail as sheet thickness is three-quarters of an inch or less.

E. Floor coverings such as carpet, ceramic tile and lightweight concrete may increase the danger due to added weight and they may insulate so the floor does not feel warm. Slide #32

F. All of this is compounded when these materials are used in large multi-family or commercial units.

G. According to NFPA Fire Analysis and Research Department statistics, 250 firefighters died of injuries suffered at structure fires from 1997 to 2006. Of those, 44 were killed inside buildings as a result of structural collapses, and another nine were outside and struck when walls collapsed. Of the 44 killed inside, 24 were killed in roof collapses in 14 fires, 17 in floor collapses in 13 fires, two in a wall collapse in a fire, and one in a ceiling collapse.

H. Full details on construction are not available for many of the collapse incidents, but trusses were involved in the collapse in seven incidents. These seven incidents claimed 12 lives. Five firefighters died in two roof collapses where wood trusses, described as pre-engineered wood and lightweight wood, were involved. Three firefighters were killed in two collapses involving lightweight wood floor trusses, and another was killed in a floor collapse involving open manufactured wood I-beams.

VIDEO Slide #34 Courtesy

VI. Changes in Tactics

A. The failure of a wooden I-beam to sag or give warning noises before complete failure is a concern as the firefighter cannot determine if there is structural trouble. University of Illinois test showed failure at 4 minutes and 40 seconds. Slide #35

B. Los Angeles Fire Department test showed failure of 3/8” web beam at just 1 minute and 20 seconds!

C. Firefighter should exercise extreme caution when:

1. Operating on a floor above a fire

2. Operating in a structure with unknown construction

D. Do not enter onto a roof supported by engineered wood products where there is obvious or suspected high heat or flame impingement

E. Utilize a thermal imaging camera to assess fire/heat with resultant structural integrity issues versus the traditional sounding method. CAUTION—Carpet or tile can trick the TIC Slide #36

F. Unless there is a life safety issue, consider a defensive exterior attack RISK vs BENEFIT ASSESSMENT Slide #37

G. The average response time in the U.S. is just over 10 minutes. Many structural elements may be near, or have already, failed upon the first unit’s arrival.

H. Darken down fire from windows and doors to prevent exterior spread of the fire into the attic via soffit vents and exposed sheathing.

I. Engineered lumber construction has been called “solidified gasoline” or a “lumberyard in the sky” when referring to multiple unit structures.

J. Make sure you have an ample water supply before an attack. Due to the extraordinary fuel load, hit multiple hydrants or call for tankers early. For large structures you may have to plan for 10,000 GPM! Slide #38

K. Large volumes of water that are required add drastically to the load on the building hastening its collapse.

L. The gable ends of the roof will burn away quickly exposing a large vent area. This will degrade the roof support system more rapidly as uncontrolled airflow feeds the fire.

M. Avoid adding additional loads to the structure that may already be severely compromised

VI. Review

• The student should now be able to identify different types of engineered wood products

• The student should be more familiar with industry terminology

• The student is now able to understand different styles of building systems

• The student should be more able to evaluate personnel safety

• The student will now be able to determine when a defensive attack is the best option

VII. Remotivation

Ever-changing construction techniques and building code changes, while improving energy efficiency and making structures environmentally compliant, have seriously impacted firefighter safety and command tactics.

Remember— Traditional training has not kept pace with the changes!

EVERYONE GOES HOME!

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