This brought back memories of my greatest exploring week ever, 7 years ago now. I did this as part of an adventure that included Ironbridge Power Station and several other sites, and not a single fail was counted that week, except for missing vital parts of this and several other sites due to lack of planning and locked doors (in the case of Ironbridge's control room).
I remember getting in to the site was relatively easy, just going through a subtle gap in the fence by the sea then running to the blast furnace, long before the PIRs appeared everywhere. One brief but close encounter of an on-foot guard (or maybe a hallucination on my part, it was only a glimpse), who was quickly avoided, then for 10 minutes we had to run around like headless chickens looking for a way up (not in, up). Getting up was climbing a staircase with no stairs because the metal steps had been removed everywhere, but luckily me and my partner were very tall, and could grapple our way up. Nevertheless it was enough to strike terror into both of us, holding onto a metal bar above our heads and shuffling our feet up one by one. Absolutely terrifying, fearing I was going to fall. We'd have to do the same thing getting out, so no comfort there.
Once we were in the blast furnace we had no idea where to go or what to see, so just walked round wherever, then crossed the conveyer belt to a building that I don't actually know was for. This was all done in the evening, so all the lights were on but there was actually very little security overall. I did see workers in one building, and I think I saw a security 4X4 driving under the conveyer, but I assumed it was a worker who was leaving, coming from the said building.
Security had actually put a crowd-control barrier up against the hole we used since we were inside, so we used this to climb back out. Ha! I saw very little of this place, but I regret nothing. It was a milestone in my exploring tenure.