"I remember the day the world changed.
I lived outside Washington, D.C. at the time. I was working outdoors - my garden always seemed to need a little tinkering, nothing really critical, but if you can't putter around in your garden, what can you do? I was working in my garden when I felt the flash. I was facing away, to the north, when I felt a pop inside my head. Not really a pop; but the light was so bright that I felt it, heard it, smelled it. I wasn't even looking at it. I ducked down behind my garden wall, but I needn't have bothered. It was only a small one, and miles away, at that. Of course, no one knew that then - you can't measure kilotonnage by eyeballing the mushroom cloud."
The mention of the garden becomes repetitive. You use the word garden over and over, three times within two sentences. I presume the point is to establish that he's at work in his garden, but the fact seems a little too well hammered. I also question the word "tinkering" in regards to a garden. Must be a man thing. I think of the word "tinkering" to be a matter of fiddling with mechanical things, like engines and such. The sound of "tink" as metal hits metal.
You say he felt a pop inside his head, then say it wasn't a pop. Then you describe it as a light, and light makes no sound. I'd like the author to make up his mind. WAS there a pop? Yes or no?
Lastly:
"It was only a small one, and miles away, at that."
The use of the word "it" bears elaboration. What is the "it" that is only a small one? I presume, given the following statment, you meant a nuclear detonation. But, if in fact that IS what you meant, then why would the POV character say "it was only a small one? It seems to me that there would be more consternation than that.
Nits:
* Tell us quickly if it's a man or woman, and maybe vague role in life (retiree?).
* a pop inside my head. Not really a pop; ... this bothered me too
* Maybe not a nit: If he/she eyeballed the explosion, will he/she be blind now?
I have a general question, though. Why revise a published work? Are you going to submit it again? Are you going to expand it? Can you submit something saying "...a version of this work was published in..."?
Please don't think I'm being snippy. I'm curious, is all. I haven't published much, and what I have published was poetry, and everyone is clear that they don't really want to see previously published poems. I don't know about genre stories.