FORT TOTTEN (AP) - Tribal firefighters on the Spirit Lake Nation Reservation are once again being run ragged by grass fires, and Chief Daniel Herman says the rash of fires is bound to end in tragedy if it continues.

The Spirit Lake Wild Lands Fire Department has battled more than 100 fires in a 1½-month period.

"We've gotten a lot of help from the community and from other firefighters, too, like the Devils Lake Rural Fire Department," Herman said. "But it just can't go on."

Fires have long been a problem on the 300-square-mile Sioux reservation near Devils Lake. Authorities say most of them are intentionally set, most often by children using matches or lighters.

This year's fires mostly have been small, though one large blaze damaged some structures in Tokio and threatened people's homes there.

Other reservations share the problem, according to the Bureau of Indian Affairs, which has established special Wildfire Prevention and Investigation teams to send to reservations with problems caused by purposely set fires. A team was sent to the Spirit Lake reservation last March.

Another education and prevention team has come to the reservation this spring, and is working to set up a tip line people can call to help law enforcement crack down on illegal fire activity.

Two experts also have been brought in to help local law enforcement investigate arson incidents.

"Using scientific methodology we can determine the fire's origin and obtain evidence for the local authorities," said Theron Oats, who works mainly on fires in Indian country.

Herman also is asking people to be more diligent about getting burn permits, which he said are free and help authorities know where and when burning is taking place. "Especially since it's been so dry and winds have been so strong this spring," he said.