> It occurred to me though — when did they start calling them "fallout" shelters rather than "bomb" shelters?
Sometime after the nuclear bomb was developed and first used to end the second world war. The "fallout" in "fallout shelter" refers to "nuclear fallout" (https://en.wikipedia.org/wiki/Nuclear_fallout) which would not have been a term that would have existed prior to the creation and first use of a nuclear bomb.
So sometime circa early 1940's to mid 1950's timeframe would be a good guess.
Sometime after the nuclear bomb was developed and first used to end the second world war. The "fallout" in "fallout shelter" refers to "nuclear fallout" (https://en.wikipedia.org/wiki/Nuclear_fallout) which would not have been a term that would have existed prior to the creation and first use of a nuclear bomb.
So sometime circa early 1940's to mid 1950's timeframe would be a good guess.