Fipronil, to my knowledge is only labeled for outdoor perimeter use. Maybe the recent “knock-offs”, now that it is off patent, will allow indoor treatment. It is safe enough indoors; its just that the original manufacturer never asked the epa to approve an indoor label. Sometimes a perimeter spray, meaning base of house and a foot or two of soil will solve a carpenter ant problem. Also spray the base/trunk of nearby trees. Fipronil is non-repellent. do not mix it with anything else or use anything else. It could take several weeks to work as it works slowly, which is what we want.
Indoors we use Phantom, outdoors fipronil. Both are safe enough to use indoors. If you want to use fipronil indoors and are still nervouse about it then just use it in the unfinished/utility/garage/attic areas of your house. Give it time and be patient.