The contractor, 35, entered the railcar to conduct an air quality test while two other men waited outside. The two men noticed he was unresponsive and began to assist him.
Firefighters determined the person in question was lying unresponsive inside the railroad tanker car, according to the department.
Authorities said the man was a contractor for a national HAZ Waste company hired to clean and test rail tanker cars.
After the fire department spoke with company representatives and monitored the surrounding areas, the department said it was determined that the employee entered the railcar with an oxygen-deficient atmosphere and succumbed to the environment as a result.
