I need a Chemical Engineer with thermodynamic experience

We are the largest provider of Substation Services in the US. We are developing new temperature indicators for use in large power transformers within the electric utilitiy industry. The device is simple to describe. It's like a CO2 cartridge except that in place of the end plug we use a rupture disc. These are to be attached to specific components inside the main tank with the rupture disc "Bursting" when the temperature reaches 250C. The cartridge is filled with Hexafluorobenzene as a trace material that disperses when the disc burst. We need to know: What is the calculated pressure within the device at 250C? What quantity would we need to have within the device to ensure the rupture disc burst reliably? What is the adverse effect if a small amount of air is entrapped during filling.