Three Union Pacific employees were taken to the hospital Friday evening after an ammonia leak in the Cheyenne rail yard.

UP spokeswoman Kristen South says the incident occurred around 6 p.m. when the pressure-relief valve on a tank car of anhydrous ammonia briefly released and re-closed.

"Repairs were made to the car, and Union Pacific is investigating why the valve released," she said.

South didn't know how many gallons of ammonia were released or if the workers were from Cheyenne.

She says the three were taken to Cheyenne Regional Medical Center for observation and released.

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