see AFCI info Consumer Product Safety Commission
Preventing Home Fires: Arc Fault Circuit Interrupters (AFCIs) at:
http://www.cpsc.gov/cpscpub/pubs/afci.html

wrote:
I have an electrician coming tomorrow to look at my newly aquired old
house which has some knob & tube in it that I have to update for
insurance purposes. The home inspector showed me how it's only the old
lighting that now uses the knob & tube, all other electrical has been
updated.

The electrician said on the phone that it's possible that he can just
add GFCIs to each knob & tube circuit to satisfy the insurance people.
This will avoid having to rip plaster walls apart.

Is this an accepted way to resolve the knob & tube issue?