According to “youmustvotenato”, the user who posted it to Reddit, the following picture was taken after the fire suppression system base went off because of a spark from a welder set.
Clearly visible in the image an F-15 belonging to the 85th TES (Test and Evaluation Squadron), an F-16 of the 40 FLTS (Flight Test Squadron), and an A-10 (most probably belonging too to the 46th Test Wing): based on the the tail codes, the hangar must have been one used by the 46th TW at Eglin Air Force Base, Florida.
Image credit: via youmustvotenato / Reddit
The foam generators suspended from the ceiling released suppressant similar to soap that submerged the planes in the hangar. It takes two minutes to fill a 90,000 square-foot hangar with more than three feet of two percent high-expansion biodegradable foam.
Here’s a video showing how fire suppression systems work.
Thanks to @Menzo2003 for the heads-up