Authorities in the Williston area said this week they'd let the fire burn itself out at an industrial warehouse used to store some of the chemicals used in hydraulic fracturing. The decision was made because pouring water on the blaze would create a secondary problem for nearby waterways.
Health officials said earlier this week they were monitoring air quality in and around the site. Dave Glatt, the environmental health chief for the department, said samples were on their way to a lab in the state capital for testing.
"We understand people are concerned about possible harm," he said in a statement Wednesday. "So far we have not found anything that causes us great concern, but we will follow through with testing to make certain public health is protected."
The Williston area is near the center of the Bakken and Three Forks reserve areas in the state. The rise in oil production there has created increased stimulus for the state's economy, but has corresponded with an increase in oil-related disasters and high crime rates.
Authorities said this week their primary health concern from the fire was from respiratory irritation.