After watching the video, it seems the cylinder rod that slides into the door to secure it (like a safe in the movies) was pried out of the door relatively easy once the weight was taken off it using the excavator bucket. I say relatively easy because I would have assumed it to be well rusted and seized in place. Now with a picture, its easier to think of many ways to open it now. I think the easiest would be to just weld some heavy metal to the end of that rod, sticking out in a direction close to where the bucket pushed against the door so that they could push on the door then bump the bucket into the Rod extension to push it out. That way nobody would have to go in there.

That being said, if this were a workplace OSHA supervised job, they probably would of had to drill into that bunker and pump out the water before even digging that hole to the door. Then Id imagine some structural inspection/testing would be done to make sure it could be worked on without collapse. The door or wall would be drilled to verify the water is out. Then after inspecting and fidgeting with the hinges and locking mechanism, send a welder in to torch off the rod and any other areas needed.

I would think that the door and hinges would be seized or stiff enough that moving that heavy door would need some rigging to pull it open or maybe weld a heavy plate with a spacer off the door so they could use a ram to push off the wall/frame. That way they wouldn't resort to cowboy mechanics like hooking up to mobile equipment and pulling the door open to skip the hassle of anchor points for the pull rigging. Though the door may open as nice as the locking rod did using some prying.

Im not OSHA or even think my way even covers close to all the safety stuff. I just work in an industrial setting doing a lot of these things, so it is easy for me to visualize and ramble (sorry) a picture for someone in case it helps or is at least entertaining. Anyway, with this scenario, the workers would just need a harness going up and down the ladder to work in the confined space. Confined spaces also need gas testing as you dont want to be in a hole where a lot of bad gases are heavy and will stay down there even with forced circulation if there is a plentiful source. That one is more for industry that has gas as a byproduct that they deal with regularly and is not as much an issue. You would want some forced ventilation for the welding and such though, as it not really arguably safe to "just go down there and torch for a little bit" then go out for fresh air. Other than that, just thinking paperwork and liability that i've bumped into, I would see environmental getting their two cents in and wanting the water pumped out and removed and might even stick their noses in for samples depending on the history of silo or land and water above.

That is my non safety/OSHA qualified business/corporate nitpicky safety overlook, which might still be too lax for some standards. If this bunker is private land or the only nosey neighbor has gone for the weekend so they can do whatever, what they did wasn't actually that dangerous. For the get er done cowboy version, they were just missing some rope tie offs to the bucket and boom to use for stabilizing while standing or kneeling in the bucket. I mention the rope here for good reason as if it was a known safety hold for them, buddy with the hat would have reached for that instead of sticking his arm around the boom and in close to the hydraulic powered pivot area that tilts the bucket. If the operator panicked or made a mistake and moved that instead of the boom, could lose limb or digit pretty quick. But im not criticizing, just trying to see the safety. I watched a couple of their videos, im sure they know all this and a lot more than i do. I just want to point out how something as trivial as a big strong pivoting crush hazard gets forgotten once the adrenalin and excitement of all that water pushing on us makes us focus that stabilizing again is priority. As it should be, I just analyzed the hazards and figured that would be a bumpy ride even without the water, and help with that. If it was seen as a safety device, it may have been instinctively used when the water hit too.

If youre still reading my ramble on safety, might as well point out the perspective baggage here is from being an industrial mechanic and my habit of reverse engineering things from their normal location. Things can be big and heavy, or awkward, or in the heat or all the above. But I don't see them as hazards, just normal. I look at the area around (usually machine or parts for one) what im working on and what it works with or connected to as an inefficiency instead. That way I seem to find easier ways to do a job or at least feel its going to go well with some foresight put into it. MAybe that ideal is flawed but at least for me, its adds to the skill and confidence going while thinking about hazards just makes the job area not fun. Thats gonna not make much sense if your main job hazard is whoever passive aggressive Cubicle Charlie will explode on when it finally happens. Its not a wall of text like this post, I just found a way to entertain myself and learn and make things a little better and easier at work.