The Colt Police Positive and Police Positive Special Revolvers had an internal Hammer Block, which would help prevent an inadvertent discharge if dropped.
Just how positive and absolute the Hammer Block might be, if the Revolver is dropped a long way on to Concrete or something, I do not know.
Personally I am satisfied with the design, and, I myself would never worry about carrying 'Six'.
When at rest, the Hammer's Firing Pin is never is resting on a Primer anyway, but, is back a little, and, within the small space of it being back a little, the Hammer 'Block' is positioned inside and down a little ways to prevent it being able to move forward if struck.
As one cocks or cycles, the Hammer Block is retracted.