Asbestos is a naturally ocurring mineral, in some parts of the country it is always in the air in trace amounts, wind blowing across factory rooftops that have asbestos "big six" panelling carries small amounts of asbestos - it was also commercially used in, to name but a few things
Paint
Artex
Plastics
Roofing Sheets
Guttering
Pipe insulation
Gasket Paper
Filters
etc etc...
Its everywhere, visit a building with it in, particularly in an open roof (ie inside a barn) you will certainly inhale a fibre.
Now the good news, only Crocidolite & Amosite (Blue & Brown) are so dangerous that a fibre can kill. More commonly Chrysotile (White) was used - it important to note that whilst Chrysotile is in the same broad family of serpentine silicate minerals, it is quite different from the former two.
Chrysotile is nowhere near as deadly as the others, the fibre and chemical structures are different, it is unknown for certain if it can cause Mesothelioma (the cancer related to asbestos) it might in some rare cases, what it does cause is Asbestosis, which is a type of silicosis which diminishes lung capacity over time, and is caused by inhaling fairly significant quantities (ie: occupational)
Just knowing you have asbestos is like just knowing you have a tree, it tells you little, a proper asbestos survey will tell you the type, risks and required remediation.
In most cases, if left un-distrubed, asbestos is safe.