Yeah, I remember this swill also ...
Well, I guess if you can see and THEN react to the flash by "ducking and covering", then perhaps you are far enough away from the blast to survive it, but how covering yourself with a thin cloth or newspaper would help you survive it better is beyond me. When I was in primary school (in the mid 60's), our school Principal periodically would suddenly announce over the PA "Duck & Cover!! Duck & Cover!!" and we would all be required to plunge ourselves under our school desks and clasp our hands over the back of our necks. Now that we, as school children were required to not only have the flash seen by an adult (aka - the Principal) but then have him react by announcing to "Duck & Cover" over the PA system, THEN we hapless kids would be able to avoid cats-asstrophe simply by kneeling under our desks and protecting our necks with our hands.