The green mist in the story reminded me of green fogs I've heard about from other stories. Green fogs have allegedly appeared in the Bermuda Triangle before. The green fogs may have something to do with some of the mysterious disappearances reported in the Bermuda Triangle.
The story of the Philadelphia Experiment also describes a green fog. The Philadelphia Experiment was an alleged military experiment that supposedly attempted to make a warship invisible. Here is a description from Wikipedia:
In most accounts of the experiment, the destroyer escort USS Eldridge, was fitted with the required equipment at the Philadelphia Naval Yard. Testing began in the summer of 1943, and it was supposedly successful to a limited degree. One test, on July 22, 1943, resulted in the Eldridge being rendered almost completely invisible, with some witnesses reporting a "greenish fog" appearing in its place.Some versions of the story also claim that the USS Eldridge teleported to Norfolk, Virginia or traveled back in time for about 10 seconds.
Wikipedia also points out in its article on the subject that the Philadephia Experiment is widely regarded as a hoax. Some parts of the story do sound a bit-far fetched, but it's possible that the story may at least be partially true. The military probably did want to make an invisibility cloak of some sort and may have attempted to do so, but whether or not they were successful, I don't know. Attempting to make an invisibility cloak would not be the strangest experiment carried out by a government around that period of time (the Nazis and Soviets were known for strange experiments too). The more far-fetched parts of the story may have been exaggerations or disinformation.
But what of the green fog mentioned in the story? Oddly enough, the green fog may be what lends some degree of credibility to the story. Bruce Gernon described seeing an "electronic fog" during an experience he had in the Bermuda Triangle. He did not report the fog he saw as being green, but he has reported seeing "green flashes" around the Florida Keys (the fog and flashes may not be directly related though).
In an interview with Bruce Gernon and Rob MacGregor that I found here, MacGregor mentions a researcher named John Hutchinson who created the Hutchinson Effect, in which objects of various materials levitate under the influence of intense electromagnetic activity. While Hutchinson was conducting experiments, a green fog appeared. So electronic fog and green fog may be similar types of phenomena. If so, could there be some kind of connection between the electronic fog Gernon described and the green fog that appeared during the Philadelphia Experiment?
So what are these green fogs? In the Hutchinson Effect and the Philadelphia Experiment, the fog seems to have been the result of electromagnetic activity induced by man-made technologies. But what about the reports of green fogs in the Bermuda Triangle or the green mist mentioned in Pastor Swope's article? Green mists/fogs aren't really all that common in ghost stories, but Pastor Swope's story is certainly not the only one to mention a green mist/fog (see a couple more here and here). So is green fog also a naturally (or supernaturally) occurring phenomena?
I'm not sure what these green fogs are. I'm not sure what causes them to be green (or appear to be green) either. Taking the man-made examples into consideration, the green fog seems to be more of an effect than a cause. My guess is the phenomena can occur naturally (or supernaturally), but the phenomena can also be duplicated by man with the right electronic technologies.
But regardless of what causes it, if you ever see a green fog, don't be surprised if something weird happens.
P.S. I left a comment on a blog posting written by Rob MacGregor mentioning that I had cited something he said in this post. In his response to my comment, he mentioned another story about green fog that he included in the book he wrote with Bruce Gernon named The Fog. According to that story, a fisherman and his partner were pursued by a bank of green fog while fishing off the coast of Florida at 2 AM. As the green fog neared them, they ran for it and called it a night.
So there is another example of green fog around the Bermuda Triangle.
P.S.S. I also want to clarify that the reason I think the green fog may lend some credibility to the story about the Philadelphia Experiment is because it happened before these other stories were written. So these other examples of green fog/mist and the Hutchinson Effect that Rob mentioned may lend some credibility to the story about the Philadelphia Experiment because green fog was also said to have been witnessed during the experiment. If the Philadelphia Experiment was completely fictional, what are the odds that the story tellers of the time would have mentioned green fog? I can't dismiss the possibility that the Philadelphia Experiment is a hoax, but it seems unlikely (though not impossible) that the story tellers of the time would have been familiar with green fog in this context.