They make a test machine that alerts to the presence of poison gas as well as other potentially dangerous environments, no canary needed. The idea is to stay out of the manhole and put the device down there to test the atmosphere.
They also make portable blowers that will purge the air down there in case any gas has built up.
Very tragic but likely very preventable.
These accidents are very avoidable. I worked at a large winery. Fermenting grapes, up to 50,000 gallons, release a significant amount of CO2. Safety belts, sniffers, and air quality testing were mandatory.
We used sulfuric acid to reactivate some of the reagent towers. I was the designated safety man if we had to enter the acid tank. The primary weighed 100 lbs, I am much larger and could one hand him out if necessary.
Full suites, belts, ropes, sniffers, and ventilators were employed.
Don
H2S is scary stuff. I've not heard of levels that high with that fast an effect in a while.
I was told a story of two brothers (here in Indiana)doing some sort of work for a smaller town on one of the towns lift stations. They worked all morning on the bottom floor, I was not told what type of work though my guess is on a pump. After lunch break was over the first brother climbed the ladder down to the bottom floor, making it some way down and fell the rest. The other brother seeing it took chase after him. They were both found dead at the bottom after not reporting in at the end of the day. My guess again, is that they took a pump off line and went to lunch without bolting a blank and the H2S in the line starting filling the bottom floors while they enjoyed their lunches. Feeling safe, as they were down there all morning, they didn't realize the danger.
I've climbed down into plenty a wet well and lift stations, much less man holes and trenches. I've had training, and I guarantee you it'd be a cold day in hell when I wouldn't instinctually go in after a buddy in harms way. I can't imagine the hell it'd be to watch your friends and co workers die in a damned hole.