My name's Isaac, and I think this is it.
It was around five-thirty in the afternoon when we saw the first blast. Hanging around outside of my apartment. It appeared first as a dull flash in the corner of my eye opposite the setting sun. All of us looked over our shoulders and could see the crest of it over the horizon.
“Holy shit!”
“What the fuck? What the hell is that?”
“Must've been a gas main or something.”
For a few moments we all stood there,  bewildered at this strange, new phenomenon. At some point somebody took out their iPhone and activated an internet news radio application, in the hope that somebody would already be talking about a sudden gas explosion that only occurred here a few minutes ago.
Nevertheless, we were all circled around the phone, listening to the radio and waiting for some information when the second explosion hit. Whereas the first one was much closer to use and had dissipated into the air after only a second or two, this one was much farther away and continued to expand long after the initial blast. Myself and those around me were all visibly disturbed by this, but we continued to watch without fear as the fireball became progressively larger and brighter. Some of us put our hands over our eyes to filter the light through our fingers. A few people who had been wearing sunglasses before the sun started to set put them back on.
I'm pretty certain most of us realized something was wrong when the first building visible to us from where we were standing, about a quarter mile down the street, was consumed by the fireball. What was once a faraway curiosity was now something very close and dangerous. A few people started to break away, then we all ran from the fireball in nearly every direction. Most of us opposite the fireball, but a few ducked into the alleyways parallel to it.
I guess the parallel-runners didn't last very long, the rest of us had only gone a few blocks when we could feel the intense heat of the fireball at our backs. Everything was so bright all around that I could only squint my eyes and obey the directions and arm-tugs of those fortunate enough to be wearing sunglasses.
I'm still running, right now. I think I'm the only one left, from my original group. Everyone else's either fallen behind or gone in another direction. I can still feel the heat at my back, it's not as intense, but I know I have to keep running. Shit, I should really-

If whoever is listening to this hasn't already noticed, I've stopped running and now I'm sitting next to some body of water that I can't, for the life of me, seem to identify. Right now I'm digging a hole in the ground here so I can bury this voice recorder that I've kept with me. I'm a journalist, actually, whoever's listening, so it's not as oddly convenient as you might think. Anyway, the reason I stopped the first recording, the one I did while I was still running, I wanted to call my parents and say my last goodbyes in case I didn't make it out. I got the machine, but I think I got my message across pretty well. It took forever, actually, I only stopped when I had to climb over a chain-link fence. By that time, the growth of the fireball had begun to slow, but if I turn around, I can still see it advancing through the city at a steady pace. I'd say I only have about fifteen or twenty minutes to finish my hole and come up with a dignified position in which to die. What really got me to stop running and everything was the sight of two more fireballs at my two and ten o'clock (the first being at my six... you know what I mean). Before that, I thought I really had a chance. Funny, right?
I figure that if whatever's happening right now doesn't destroy the world, corporations are going to want to market the hell out of it, and they're going to need some kind of dead-man's story to sell books or movies or something. I'll probably be one of hundreds, but maybe they'll like the way I tell it.
Sorry if my voice is breaking, but the fireball is starting to get close and... well I don't know if you've ever just sat and waited to die before but... it's pretty fucked up. I have to hurry and bury this thing, god I hope this hole is deep enough. I think it'd be a shame if I went through all this running and talking for nothing. I'm sure all the dirt and heat will have some kind of effect on the hard drive but... that's what data recovery is for, right? Shit, that's it, no time left, I have to-