VIENNA, Mo. — Investigators determined a house fire and explosion that injured six firefighters in rural Missouri was intentionally set.

The Maries County Sheriff Chris Heitman said the explosion occurred Friday morning while firefighters were extinguishing a blaze at a house in the 13000 block of Highway 28 West.

It happened outside Vienna, Missouri, which is about 120 miles southwest of St. Louis.

Firefighter Mason Smith said they were just beginning to attack the blaze when the house exploded.

The injured firefighters were rushed to hospitals in three communities. Five of them were treated and released; the sixth had to stay overnight. Smith suffered second-degree burns to his fingers.

“It doesn’t look pretty and it hurts,” he said. “They gave me pain enough medication.”

The injuries ranged from moderate to severe burns and cuts from flying debris.

The Missouri State Fire Marshal and Maries County Fire Department have been handling the investigation together.

Maries County Sheriff Chris Heitman said the fire department is made up of volunteer firefighters and the injured first responders will likely miss several days of work.

The Vienna Fireman Relief Fund has been established at the Maries County Bank. Sheriff Heitman will turn those funds over to these six firefighters on Wednesday.

No arrests have been made as of yet. The sheriff has pledged to bring the person or persons responsible to justice.