A father and his son were killed by noxious fumes from a hog manure pit in northwest Iowa on Saturday, the second father and son to die from manure fumes in the Midwest this month.

Gene Opheim, 58, and son Austin, 32, who were from Cylinder, Iowa, were rescued after the Palo Alto County Sheriff's Office got word of two people trapped at the bottom of the pit at 1:50 p.m. on Saturday.

Both were declared dead after they were taken to a hospital in Emmetsburg, succumbing to the poisonous gases, according to the Daily Mail.

The accident took place after father and son were doing repairs in their farm, when one of the tools they were using to fix a pump at a hog confinement fell into the manure pit.

The son tried to retrieve the tool but was overcome by the fumes. His father went it to try and rescue him, but both ended up getting trapped below, according to the New York Daily News.

A deadly combination of hydrogen sulfide along with methane, ammonia and carbon dioxide begins to form once the manure starts to decompose and it only takes a few seconds for  ormal work in a pig barn to take a turn for the worse.

"When you're working in the animal environment, you're relatively safe. But whenever you're working below the slats, or where manure is being disturbed, that can be highly dangerous," said Daniel Anderson, who is a water quality and manure management professor at Iowa State University, according to The Des Moines Register.

Anderson added: "When something breaks the surface of the manure or if the person is in the manure, moving around, that causes more hydrogen sulfide to come out of the manure."

"That can cause unconsciousness and untimely death," he concluded.