You hear of workers dying in sewer manholes ever so often. They should use ventalation but sometimes they think, "I'm only going to be down their a minute." They pass out, another one goes in after him and it just gets worse.
Farm silos, especially after harvest, are very dangerous places to be around. I've seen dead rats, mice, cats, birds, etc. near the foundation of them right after they have been filled.
I used to sell and service silo unloading and feeding equipment. I had one farmer cuss me for 15 solid minutes because I wouldn't go into one and set up his unloader right after harvest. I told him to call me in 2 weeks and left.
I heard he buried one of his farm workers later that week.