I'm going to declare a new law, a la Bettredge's Law: "When a small probability is claimed, without evidence, to be less than that of death by lightening strikes, it is safe to assume the small probability is in fact higher than the risk of death by lightening strikes".

Find me the evidence and I'll admit that my new law is invalid. :)

I don't need evidence to know that the odds of casualties falling into a modern well (that is a few inches in diameter) such as the one being drilled here are less than being hit by lightning (assuming lightning is possible).

I won't rule out the possibility of an ankle sprain.

The biggest risk of construction comes from handling the concrete rings. I haven't heard of a suffocation accident. These are much more common when people maintain their sanitation tanks.