Pig farmer Leon Sheets knows that pit foaming is a dangerous phenomenon. He’s got the scars to prove it.

Sheets, a Chickasaw County Farm Bureau member in Ionia, starting disinfecting an 8-foot-by-40-foot area of a finishing barn on Sept. 14, 2014.

The work area had slatted floors and was situated between four rooms in the building. The ventilation was on low. The room...