A dodgy geezer I used to know, who ran heavy plant, explained it to me once, while he was telling me how you can use transformer oil as a substitute for diesel (thus evading duty) but that you have to add something to it as it doesn’t lubricate the engine sufficiently well by itself. I can’t remember the details (and I never did put transformer oil in my car, nor did I ever call it ‘tranny oil’ as he did
).
I think it has something to do with the fact that it has to sit inside a sealed system for an extremely long time without causing corrosion, and needs also to be an electrical insulator. As long as it stays where it’s supposed to be it can’t combust, but a risk of using oils in transformers is that if the transformer’s casing fails in some way and the oil leaks, then it can cause a fire.
If this wasn’t the Russians (and I don’t think it was, if they knew the could cause this much chaos with one act of vandalism they’d surely have held on to the info until they really needed it); and it wasn’t random vandalism (which would seem unlikely seeing as you would risk killing yourself before getting anywhere near the bit that caught fire) … then we’re looking at poor maintenance as a potential cause. I don’t want to prejudge the inevitable inquiry but, let’s face it, none of us would be surprised at that would we.