Three persons were sickened Tuesday afternoon when they were apparently overcome by carbon monoxide poisoning at their place of employment, Technical Process and Engineering along SR443 in Mahoning Township. The incident began when the three were transported to the Lehighton hospital and treated for their symptoms. When it was learned they had high amounts of carbon monoxide in their blood, hospital officials notified the Carbon County Communications Center. The Mahoning Valley and Lehighton fire companies were dispatched to the site as well as the Mahoning Valley ambulance. The plant was evacuated as fire officials checked the air quality and looked for the source of the carbon monoxide.