Here are some detailed studies that look at different hand drying methods and how they relate to hygiene.
Comparison of electric hand dryers and paper towels for hand hygiene: a critical review of the literature, The University of Arizona
A comparison of effect of three hand drying methods on washed hands: P. J. Pardeshi (Global Journal For Research Analysis (GJRA)
Simplified Environmental Assessment of the Federal environment Agency (VERUM): Bundesumweltamt (from PDF p. 118)
Life Cycle Assessment of Paper Towel and Electric Dryer as Hand Drying Method in The University Of Melbourne
A microbiological evaluation of warm air hand dryers with respect to hand hygiene and the washroom environment: Journal of Applied Microbiology