An interesting article in a peer reviewed journal: "Photographs and analysis of an unusually large and live-lived firewhirl"
The current edition of the "E-Journal of Severe Storms Meteorology" (a peer reviewed meteorological research journal). I mention this since there is a rather interesting article:
Umscheid, M.E., J. P. Monteverdi, and J.M. Davies, 2006: Photographs and analysis of an unusually large and long-lived firewhirl. Electronic J. Severe Storms Meteor., 1, no. 2, 1-13.Here is the abstract and the path to the full article.