Hutchinson ? An ammonia leak at a Tyson Foods plant sent nine workers to the hospital Saturday night.

It was the second ammonia leak at a Hutchinson-area Tyson plant in less than two months.

Plant officials said they discovered Saturday’s leak in an engine room around 8:15 p.m. and thought it was caused by a malfunction in an oil filter. They said the leak released more than 100 pounds of ammonia.

About 35 employees working at the plant were evacuated. Two women complained of chest pains and seven other workers were coughing and taken to a hospital, said Hutchinson Fire Chief Kim Forbes.

Forbes said the plant’s valves were closed immediately and the leak was isolated just after 9 p.m.

This was the plant’s third leak in 13 years, said Jim Roberts, complex safety and environmental manager for Tyson. The plant makes bacon and tacos.

Roberts said the plant, which employs 120 people, would be open at its normal time Monday.

An ammonia leak from a broken refrigeration line killed an employee Oct. 31 at a Tyson plant in South Hutchinson.