I'm concerned that the insulation/ cardboard foil that's behind my recessed radiator is asbestos. My house was built in 1960. Does anyone know if they made that stuff with asbestos? Before purchasing my home I had the insulation checked in the attic and also in the old boiler. I was glad to find out that there was no asbestos.
If it was my house I would not worry about it if it was intact (but I would not disturb it either), significant friable spread by convection alone seems unlikely. If I had kids... better safe than sorry, hire an asbestos abatement firm to test and remove/replace if necessary.
OSHA PEL (Personal Exposure Limit, max exposure over 8 hours on a time weighted average) is 0.1 fiber per cubic centimeter, max exposure over any 30 min. period is 1 fiber/cm³.
There's no particular reason that it would be asbestos. Cardboard would work just as well as an insulator behind the foil reflector, and wouldn't be any more of a fire hazard than any other boxes you have in your house.
I'm not making any promises -- asbestos was a Miracle Material when it was new, and was used for all sorts of things that didn't absolutely need it -- but I'd be surprised.
If you're worried, you can have a test done, but that has the downside that (a) once you know asbestos is present, you are obligated to tell any future buyer unless you have properly remediated the problem, and (b) the advice short of that may indeed be "since it's undamaged, just leave it alone and it will leave you alone."
But it may be worth the cost to know for certain, especially if you have young kids in the house who might tamper with it. There are undoubtedly contractors in your area who are certified to deal with this. There are also semi-do-it-yourself test kits similar to the mold tests (use a fan to pump air through a filter, send the filter to the lab and they examine it for any evidence of asbestos), but those can only tell you whether there's a problem now, not whether it's a potential problem for the future.