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38
FIGURE 12 Schematic diagram of the laboratory tunnel facility of Carleton
University (31).
This facility was recently used to study the impact of tunnel There is a need for full-scale fire tests using real vehicles to
suppression on tunnel ventilation systems. The absolute cool- verify FHRRs with fewer corrections to local conditions.
ing effect and radiation attenuation were examined by activat-
ing the sprinkler system over a propane fire, which generated a A set of full-scale tests in Europe provided valid information
constant HRR. The test examined the effectiveness of the lon- on HRRs from cars and HGVs. Limited information was pro-
gitudinal ventilation system with the sprinkler system active. vided on bus fires and no information on gasoline tanker fires.
When the sprinkler system was turned on, some smoke escaped
from the tunnel openings; however, overall, the ventilation sys- The UPTUN fire tests did not provide much information on
tem was able to control the smoke. The sprinkler system cooled smoke and other gases dissipating from the fire during the tests.
smoke, caused steam formation, and lowered visibility. With Smoke dissipation data were obtained during tests in Japan
the sprinkler system active, ceiling temperatures upstream of and information appeared in the PIARC and NFPA 502 docu-
the fire and in the spray section dropped dramatically. It was ments; however, those tests were outdated and the smoke
found that the sprinkler system and ventilation system effec- production rate was removed from the documents. Design
tively cooled down smoke and reduced the heat flux. The mea- engineers are advised to select a material, such as polystyrene,
sured heat fluxes showed that the absorption of thermal mineral oil, polyurethane foam, or wood cribs to calculate
radiation and transmission of the radiation can be affected by smoke production rate. It was noted that smoke was the leading
the sprinkler system and air flow in the tunnel. The longitudi- cause of death. A lack of such information could be considered
nal air flow in the tunnel was affected by the discharge of water as a significant gap in fire testing. Some observations made
sprays because the air flow velocity was as low as 1 to 2 m/s during recent fire events noted that smoke is produced faster
(197 to 394 fpm). However, the ventilation system was able to than the fire grows. This may be associated with the materials
control smoke in the tunnel. As the sprinkler system reduced burning first. Modelers typically use a linear relation between
the smoke temperature, it could be expected that the driving the HRR and smoke production rate, which may lead to under-
force to propagate the smoke decreased, thus enabling the lon- estimates of smoke development during the evacuation phase.
gitudinal ventilation system to prevent backlayering of smoke.
Numerical modeling has become a tool of choice for design
engineers modeling tunnel fires. Designers need to select
GAPS IN FIRE TESTING, MODELING
LIMITATIONS, AND COMPUTATIONAL FLUID
appropriate physical models and boundary conditions to
DYNAMICS VERIFICATIONS model fire events. One of the unknowns is the turbulent model.
It has been demonstrated in the past that different turbulence
The Memorial Tunnel Fire Test program produced a substan- models and different coefficients in those models can lead to
tial amount of valid information and test results for further different (sometimes opposite) results. Design engineers often
studies. However, the program used fuel pans to simulate fire. uncritically use turbulence models proposed by the CFD pack-
There have been no full-scale fire test programs with real cars, ages and some default coefficients with little if any under-
buses, and trucks in the United States. The National Fire Pro- standing of the accuracy of their selection. However, there
tection Association (NFPA) uses information on HRR from the were no road tunnel fire tests that required instrumentation that
tests performed in Europe and Japan, but recognizes that the would allow for the measure of turbulence scale. Therefore, the
open trucks tested in those countries are not used in the United user inputs the recommended turbulence models and model
States. It also recognizes that test conditions did not represent coefficients, which can lead to incorrect design or speculation
typical road tunnel geometry, but used smaller tunnel sections. on the modeling results.
