FULL SCALE FIRE TESTS ON TIMBER CONSTRUCTIONS

Xiao LiArup Shanghai

Objective

To study the fire performance of combustible constructions in a natural fire,

■ fire behaviour in CLT rooms protected at different levels, i.e., Fully exposed(2 tests), fully protected(2 tests) and partially protected (3 tests)

– Room temperature and heat release rates– Contribution of timber structure to room fire size– Charring rates and depth of timbers

■ Comparison to fires in traditional light frame rooms (3 tests)

■ CLT structural capability under fire is not considered

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Design of fire tests

■ Tests conducted during 2012 to 2013 at Carleton University Fire Lab, lead by prof. George Hadjisophocleous

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GB

Test Design: room construction

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Exterior Room Size:3.5 m x 4.5 m x 2.5 mDoor (single opening) Size:2.0 m x 1.1 m

CLT Panels are used for walls and roofs3-ply CLT panel with a 105 mm thickness, adhesive is polyurethane.(by Nordic Engineered Wood)

Gypsum boards protection: 12.7 mm fire rated gypsum board(double layer protection)

Floor: 19 mm hardwood tongue and groove maple flooring

2.5m

3.5m 4.5m

2.0m

1.1m

Test Design: room configuration

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Unprotected

Walls

LSF+1GYP

LTF+1GYP

LTF+2GYP

Unprotected

Walls

Test 5

Unprotected Wall

Test 6 Test 7

Test 9

Test 8

Test 10

Test Design: fire load

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Fire loads are the same for all the tests, including: Queen size bed and bedding + 2 nightstands + Dressers and drawers +clothes + wood floor

Total fuel load ≈ 8400 MJ Fire load density: ≈ 550 MJ/m2

Test Design: data measurements

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Thermocouple trees:

Plate thermometers:

Wall thermocouple groups:measure temperature inside the walls at different depths;Embedded into the wallsUsed to detect charring depth

Test Design: HRR measurements

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▪ Fire room located inside the tunnel

▪ Oxygen Consumption Calorimetry System to measure HRR

▪ Heat release rate = HRR inside the room + HRR outside the room

Pillow is ignited with square propane burner

Temperature: fully protected vs. exposed room

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Heat release rate: fully protected vs. exposed room

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Heat release rate: fully and partially protected room

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Data lost

Room temperature: fully and partially protected room

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CLT delamination vs. 2nd flashover

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In Test 5 (two adjacently exposed CLT walls):

2nd flashoverafter delamination

Premature delamination leads to some flares

Re-ignites due to delamination of first ply

The fire regains strength

Contribution of timbers to fire

■ Total heat production comparing fully protected room with fully exposed room

– heat production from exposed timber panels increased the total energy release by over 60% of in both Test 1 (full exposure+propane) and Test 3 (full exposure+furniture)

■ Internal vs. external heat release rate (peak average)– further calculation showed that about 75% of the heat release

occurred outside the room during the fully developed period in Test 3 (full exposure+furniture)

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Test 3 (full exposure) Test 4 (full protection)Mean THRR (MW) 7.11 3.995Global combustion efficiency 58.4% 67.6%Fuel burning rate (kg/s) 0.676 0.328Doorway Air entrainment rate (kg/s) 0.856 1.076Smoke outflow rate (kg/s) 1.532 1.404Neutral plane height (m) 0.78 0.87Global equivalence ratio inside the room 3.056 1.18Maximum in-room HRR(MW) 2.58 3.24Heat release rate outside the room (MW) 4.53 0.775

Contribution of timbers to fire

■ Effects of the area of exposed CLT panels inside the room

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Test # heat production in thefirst 26 minutes (MJ)

Ratio to Test 4

Test 3 (full exposure) 9864 2.15Test 4 (full protection) BASE 4581 1Test 5 (2 adjacent wall protection)

5275 1.15

Test 6 (2 opposite wall protection)

6702 1.46

Test 7 (1 wall exposure) 4383 ≈1

total heat production in the first 26 minutes of tests

Light timber frame

25 minutes after ignition

Contribution of timber studs in LTF

Fire performance of gypsum boards

■ Two layers of 12.7mm fire-rated gypsum board delayed the onset of charring (i.e., 300 ᵒC)

– not charring occurred in fully protected room tests Test 4 and Test 8 before extinguishment (> 50 minutes) (with Furniture fire)

– Onset of charring at 43 minutes in Test 2 (with Propane fire) – By over 80 min in Test 5 and by over 50 min in Test 6 (test ends

at 56 minutes)

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Charring rates of CLT in room fires

■ Charring rates varies with fire size/room temperature

■ Increase charring rates after CLT delamination (1 mm/min)

■ Highest average charring rates were found in one measuring spot in Test 3 (fully exposed CLT room+furniture): 1 mm/min in a 60-minute period

■ Average charring rates in Test 1,2,3 over the test periods were 0.69,0.77, 0.71 mm/min, respectively.

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Summary■ Fully unprotected CLT panels in fire: >60% of total heat production compared

with full protected room.

■ In the fully exposed CLT room, almost 2/3 of the heat release occurred outside the room during the fully developed period

■ Room temperature is not affected by the area of exposed timber panels (ranging 1000 to 1200 Celsius during fully developed period)

■ Delamination of CLT panels could cause an increased charring rates and fire intensity (even a 2nd flashover), and a self-distinguish fire may not be always reached

■ Area of exposed heavy timber panels (e.g. CLT) affect the fire intensity:– The fire in the room with two facing exposed timber walls contribute more

to room fire than the room with two adjacent exposed walls– Second flashover occurs when more than two CLT walls were exposed– With only one timber wall exposed in the room, the fire intensity is similar

to the fully protected room, no 2nd flashover

■ CLT overall charring rates during the real fire could be higher than the standard charring rates 0.65 mm/min; but it is still predicable below certain limit

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THANKS

The background is what happened to exposed CLT after fire

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