| Résumé | A series of 2-m pool fire experiments were performed to better evaluate the comparative thermal hazard between different crude oils as a result of pool fires, which could occur as a consequence of an accident in the land transport of crude oils. In order to assess the thermal conditions to which a rail tank car could be exposed, a calorimeter designed to simulate a 1/10th scale tank car was placed above a 2-m diameter pool fire fueled by heptane in Series 1 tests, Bakken crude oil from North Dakota in Series 2 tests and diluted bitumen (dilbit) crude oil from Alberta in Series 3 tests. The calorimeter was instrumented to measure the total heat flux at various locations along its surface.
The crude oils used in the testing program were specially handled to ensure no change in its composition over the course of the testing program, from the time of fuel acquisition to the time of fire testing. In conjunction with the fire testing, a fuel characterization study was conducted to enable the study of fire effects in relation to fuel properties.
The burning behaviours of the fuels were observed by measuring the burning rate, flame height and heat release rate (HRR), the flame surface emissive powers (SEP) and the incident heat fluxes away from the fire. Overall, the Bakken crude oil and heptane fires displayed continuous steady burning throughout the test while the dilbit crude oil fires displayed unsteady burning behaviour, which was mainly caused by the fuel composition containing a larger fraction of heavy end hydrocarbons than the Bakken crude oil and heptane.
The total heat flux measured by the calorimeter indicated that the measurements were uneven around the circumference of the calorimeter. The average heat flux to the calorimeter from the Bakken and dilbit crude oil fires was higher than that from the heptane fires although the measured HRRs of the Bakken and dilbit crude oil pool fires were less than those of the heptane pool fires. The main reason for the increased heating of the object in particular by the Bakken and dilbit crude oil fires is that the total heat flux to the object is mostly affected by radiative heat exposure from the flame, and the Bakken and dilbit crude oil fires have higher radiative heat fraction.
The study also investigated the effects of test parameters on fire characteristics. These parameters include the effect of fuel types, the presence and placement of a calorimeter engulfed in the fire, fuel feed temperature, and allowing the fuel to burn down. The results indicate that there was no significant effect of “fuel supply temperature” and “fuel to burn down (i.e., non-continuous fuel feed)”. The higher fuel supply temperature increased the burn rate by about 10% for the heptane and Bakken crude oil tests. For the dilbit crude oil fires, due to the non-steady burning behaviour, the impact of the calorimeter was difficult to capture. Allowing the fuel to burn down, rather than maintaining a constant fuel level in the pool pan, resulted in minimal effect on average values of the mass burning rate and general fire characteristics of the Bakken crude oil pool fires. For the dilbit crude oil, the fuel compositional effect on the burning behaviour was observed in both continuous and non-continuous fuel feeding. The non-uniform burning behaviour became easier to discern when there was no continuous fuel feed into the fuel pan. |
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