There's another explosion sprite that I've noticed in three games so far and I'm not sure where it came from. The earliest appearance is MegaRace (DOS), and I was able to properly rip it for the first time recently:

I found out yesterday that Rise of the Triad uses the same explosion sprite.

And lastly, the same sprite can be seen yet again in the 3DO port of Microcosm. All three examples are in the image attached to this post.
The MegaRace explosion file used RLE to compress the pixel data and then it was further reduced in size with Cryo Interactive's custom HSQ compression. I highly doubt any dev at the time would've have done all this work to get access to this asset, so it has to be from some image or video clip library.
The Rise of the Triad explosion appears to be slightly different as well, there's extra detail on the edges of the explosion that don't show up in MegaRace; ROTT and Microcosm's sprites are also missing the little bits of debris at the end of the animation.
I hope whatever library this explosion is on has been preserved. Unless I missed something, I don't see anything similar in Pyromania, Pond5 or even GettyImages.
EDIT: Someone did a sprite rip of Rise of the Triad and there's several other flame and explosion animations in here that are most likely from the same library, so that could be useful.