A spokesman for Northern Constabulary said: "Two male estate workers and two female ambulance personnel were taken to the Western Isles Hospital following precautionary decontamination as a result of an incident.
"Both ambulance personnel and one of the estate workers were discharged following assessment. One man is due to be discharged following further assessment."
Police said the fire and rescue service is assessing the property to make sure it is completely safe.
"There is not believed to be any further risk to the public," the spokesman said.