[Arran]

 There is a great deal of hysteria about asbestos, a lot of which has been spread by civil trial lawyers and "Remediation" companies hoping to "Clean Out" someone's bank account. There are three different types of asbestos that have been put to commercial use, Blue asbestos (Crocidolite) Brown asbestos (Amosite), and White asbestos (Chrysotile). White asbestos is what you will find in radios, it was what was mined in North America and accounted for 95% of the asbestos used here, and it's the least hazardous of the three, it takes a lot of long term exposure, in large quantities, to cause health issues. As I said on the alternative forum, unless you are grinding it up and snorting it you really don't have anything to worry about, if it's falling apart, pick it up and toss it in the garbage. think of it like solder, it has lead in it, if you don't stick it in your mouth or eat it you won't get lead poisoning. Heck those 46-1201s have a mercury switch in the mechanism, heat up that mercury, and inhale the fumes, and you can die in one sitting. The thing to keep in mind is that it is a naturally occurring material, so there is always a certain amount of it in the air due to erosion, not to mention it was used in brake linings for decades. If the sheet is in good condition, and it really worries you, you can paint it with something like furnace cement or latex paint to seal it up.
Regards
Arran