Fire Testing and BLEVE Research at Queen's University
Department of Mechanical Engineering
Queen's University
Kingston, Ontario CANADA
key words: boiling liquid expanding vapour explosions ( BLEVE ), thermal protection, fireball, blast, jet fire, projectiles, pressure relief valve, pool fire, torch fire
The latest test program for Dr. Birk and his team to work on was the Thermal Protection Defect Field Trials in the summer of 2004. This field trial is a follow on from the BLEVE Testing and PRV Testing programs conducted by Dr. Birk and his research team.
The Thermal Protection Defect Trials involved the use of 500 gallon ASME code propane tanks as models of 133000 gallon tank-cars. The diameter of the 500 gallon tank is about 1/3rd that of the full scale tank car. When it comes to tank fire exposure, many of the important factors scale with the diameter. For example, time to failure scales with the diameter. An unprotected tank-car in a fire would fail in around 24 minutes, while the 500 gallon tank in the same fire would fail in about 8 minutes. The 500 gallon tanks were heated by a 25 x 25 array of liquid propane fueled burners. The burners were used (rather than pool fires) to ensure test-to-test repeatability of fire conditions. The mechanical pressure releif valve (PRV) was replaced with a computer contilled high speed ball valve. It was learned in previous tests that PRVs are highly variable and this effect was eliminated from these tests. The object of the test was to show if tanks with small thermal protection defects can fail (i.e. rupture or BLEVE) when engulfed in fire.
Thermal protection is used on tank cars to slow the heating of the tank if it is exoposed to engulfing fire in an accident. Recent studies have shown that tanks may have some defects in the thermal protection systems. Dr. Birk has been modelling these defects and these tests were needed to validate the model for small defect cases.
This work was funded by the Dangerous Goods Directorate of Transport Canada through the Transportation Development Centre. The tests were carried out at the Munitions Engineering Test Centre (METC) of the Defense Research Establishment ValCartier (DREV) in Quebec Canada.
Six propane tests were conducted in the summer of 2004. This included two baseline tests (no thermal protection) and four tests with defects in the range of 8-16% of the tank surface.
The following Figure shows the tank ready for the test. You can see the burners. The defect is under the black steel jacket located directly under the burners. This burner systems provides approximately the same total fire input as a 25% fully engulfing fire with an effective fire blackbody temperature of about 850 deg C.
The next figure shows the same tank with the fire on. As can be seen the jacketed portion of the tank is engulfed in fire.
The next figure shows the tank after the test was complete and the tank had ruptured. As can be seen this tank ruptured but did not BLEVE. The failure opening is quite large and this resulted in a massive 2-phase propane jet and large transient jet fire. The force of the jet split the 3 mm thick jacket open. The tank wall thickness was 7.1 mm and the wall reached a temperature of about 700 deg C at failure
The next figure shows the result of a baseline test of an unprotected 500 gal tank. This tank failed in 8 minutes as expected. It did not BLEVE because the failure was so rapid that there was not enough time to store enough energy in the liquid to cause a BLEVE. The release was a massive 2-phase jet release and jet fire. Note that the tank still contains refrigerated propane.
The last figure shows the baseline test result again. From this view you can see the massive distortion of the tank at the rupture.
The results of this test program show that even relatively small defects in thermal protection can lead to tank rupture if the fire is severe and if it is applied directly to the defect area. This data has been used to validate Dr. Birk's tank thermal models. These models will now be used to assess various types of defects in tank thermal protection systems.
For more information the reader should contact A. M. Birk at Birk@ME.QueensU.ca