Ok [@Grombus]. I'll give you a few options. 
You can pass through the fire, but you will take serious damage (see my fire video link previously). 
You can try to circle around and take out the flamethrower crusaders from a different angle. You will likely be faster than them and should be able to pull this off. 
You can write that one of the flamethrowers miraculously glitches out and Void is lucky and fast enough to take advantage of the opening.
You can write that Void needs help, and I am certain Rhyss, Magnus, Hale, or maybe even Martin will help you, which might make for some fun rp. 
You can make the flamethrower crusaders sick. 
You can come up with your own option.

As for the Holy water vapor, as a vampire, you have to be affected by it to some annoying, inhibiting degree. As an oldblood, it's not going to incinerate you, but it might cloud your vision, or burn your skin, or sap/nullify your disease power, or weaken you, or slow you down, or make you cough, and generally be repelled to some degree. 

A couple questions, I kinda know how old Void is, since you pm'd me, but how strong would you say his healing is, and how fast would you say his speed is, compared to say... Magnus or any of our other characters?