i have used them inside the open cabin of a boat. worked well with no side effects, with no side effects, with no .....
. ive used them in many different scenarios and they are very effective
its such a pity that they only last 4 hrs. depending on the amount of alcohol consumed, it coincides with the need to pee so just reload and go again
you always know when the thing needs changing by the number of mossie/midge bites you end up with
ive seen people (not me of course) modify the bottle so refilling was possible and use other brands of pads. reduces the cost of the original refills
SMC, I used only 2 cards and one 100ml bottle of gas, over 4 nights, for 3 hours each nite, just this last week, with the last hour of the night being inside in the camper. They are the best bug driverawayer, I have ever used, I still have at least one more night of gas and one card to go with the thermacell. Makes sure you buy extra's of cards and an extra 100ml bottle of gas, for the handheld unit, or alternatively, get the one that screws in on the 110gm, 260gm or 460 gm gas bottles they last weeks.
The only time I get them out is while fishing on rivers/waterways where mangroves are present.
These areas are notorious for mossies and midges ALL DAY AND NIGHT.
That's why you need to use them constantly
I occasionally use one of the paddle shaped units inside and place it on an overhead shelf. Thermocell insecticide tablet/pads are no different to ones you plug into an AC powered GPO unit and these are meant for indoor use. The tiny heated filament is well inside the body. It would take quite an effort to smash exposing the filament without the gas cartridge disconnecting at the same time. A fridge or HWS pilot light has a greater risk of spreading fire.
Burning butane creates carbon monoxide which is the likely reason for the not to be used indoors. If all windows and doors were open it should be fine. But in our van there is no need, with midgeproof screens and keeping the screens shut you really shouldn't get enough mozzies/midges in the van to ever need it.
Active ingredient is allethrin. Non-toxic to humans, not so friendly to mozzies, bees, fish and cats. Same stuff is used in most plug-in zapper pads. There are far worse things in most aerosol insecticides.
It isn't the repellant, it is the butane. Burning butane creates carbon monoxide which kills. If you used it in an enclosed area without all the windows open it would have exactly the same consequences as using a butane heater or other butane appliance that produce carbon monoxide, first you get sleepy, then you go to sleep and very possibly never wake up.