Another worker in India told of a time he went with three co-workers to unblock a manhole. And it was quite a deep one. So at some point he went out for a break, to have a cigarette. And when he came back he realized that his co-workers – who were still inside the sewer – had lost consciousness because of toxic gases, likely ammonia or carbon monoxide or sulfur dioxide. He immediately went in to try to save them and he fainted as well. Ultimately they were taken out of the manhole by an ambulance crew. He survived, but it took him three weeks to recover. And his three co-workers, because they had been exposed to the gases for longer than him, all died.
Another problem is that it's quite common for people to smoke or use alcohol to numb their senses for going into the pits. And that can increase the risk of accidents. And of course it can lead to addiction over the longer term. Also, sometimes the latrine pits collapse. The worker will be inside the pit emptying it, and there's a separating wall that can cave in.