The spring open burning season will run from March 1 to April 30. Burners must call the Ventilation Hotline daily at 751-8144 or check online at www.flatheadhealth.org before burning. The hotline and the Web site are updated daily before 8:30 a.m. Weekend information will be available on the hotline by 5 p.m. on Fridays. Prohibited materials include all man-made materials, treated materials, wood and wood by-product trade wastes. Construction debris is considered a trade waste. Campfires and warming fires are restricted to less than three feet in diameter and consist of materials less than three inches in diameter.