Workers at a northwest-side cement plant were exposed to cement powder Monday morning when a silo valve malfunctioned and dumped the material onto them. 

Two employees of the Staker Parson cement plant, 5400 W. Massingale Road, west of Interstate 10, were working under a silo containing cement powder when the automatic control valve malfunctioned and caused the silo to remain in the open position shortly before 6:30 a.m., said Capt. Adam Goldberg, a Northwest fire spokesman. 

When crews from the fire department arrived their first priority was to decontaminate the employees by washing the cement powder off them using hoses, Goldberg said. 

One of the ingredients in the cement powder is limestone which can cause chemical burns. 

Both men had respiratory complaints and one man had eye irritation, Goldberg said. 

They were both taken to the hospital for further treatment. 

Two other employees worked for about an hour to plug the silo to keep the cement powder from continuing to leak out. 

They wore basic protective clothing, but also had to be decontaminated, Goldberg said. 

They were also taken to the hospital for further evaluation.

All of the men were released from the hospital before noon, Goldberg said.