Yes, I am using incompressible-ideal-gas, and I put the initial density on the specified operating density.
I've looked up some materials and they say if I use the incompressible ideal gas option, I should put 0 in the specified operating density. Wondering if that is correct and if it makes sense?
Lastly- Could you tell me what I will have if I adopt incompressible-ideal-gas and not specify the operating density? Would the bouyancy caused by the fire be generated? I am still very confused about this operating density option.. and about what it does. 
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