The room has fire suppression technology (TNG Up the long ladder) or in this case, selective fire suppression. He must have gotten permission for the candle but the AI in charge of monitoring the room would have been on top of any non permitted fire.
(Force fields appear surrounding open flame, and the fire runs out of air.)
Of course it's also possible that Tuvok kept his shit together for 5 minutes and turned off the fire suppression technology?
All the tactical officer needed to be cured was to get a healing meld from a compatible Vulcan, before the damage became irreversible.
So... Um?
Why didn't she bring a gorgeous Vulcan Doctor with her?
"I knew it was a one way mission"
Bullshit.
OMG.
If Janeway could have brought Selar with her to cure Tuvok. That professional would have turned the EMH unceremoniously off because he is training wheels that she does not need.
That would have been a fantastic end to his story.
"You are not real, and very annoying. Computer, uninstall program."