Before we had this regulation, tragedies like this were not uncommon:
Toxic gas kills six workers
Shanghai Daily News
SIX employees of a drainage company were killed by toxic gas in China's northwest when one fell into a well and five coworkers tried to rescue him, the government said Monday.
The disaster occurred Sunday in Qiemo County in the Xinjiang region of China's northwest, the official Xinhua news agency reported, citing local authorities. It identified the gas involved only as "marsh gas."
One worker fell into the well and was overcome by toxic gas, and six coworkers succumbed to the gas when they tried to rescue him, the report said. It said five of the coworkers died and one was hospitalized in serious condition.