The article "From Sheep to Shop" includes a thorough description of wool carbonization, the treatment of wool during large-scale commercial processing to remove chaff.
According to the article carbonization puts wool through a dilute sulphuric acid solution, baking, crushing, neutralizing, washing with soda ash and soap, and bleaching with hydrogen peroxide. The article is at http://www.woolipedia.com/fromsheeptoshop.html.
To avoid carbonized wool, you buy wool at the raw or scoured stage, or buy prepared wool from a company that uses other methods of coping. For example, rollers can crush chaff, or the miller can accept only fleeces from clean pastures and/or sheep that wear coats.
I am contemplating a wool purchase and I'm giving some thought to these considerations. BFL top is so wonderfully, consistently white and free of bits. Scoured wool that I buy and then comb will mean a fair bit of effort to source and to comb. It might yield streaky wool with bits I have to remove while spinning. On the other hand, it might be softer and more lustrous.