Flammability of Christmas Trees

Abstract

The flammability of conifers used as Christmas trees depends mainly on the foliar moisture content and also on the crown density. Trees allowed to dry can be ignited with matches when the moisture content falls to about 50 per cent, and will burn with great violence when moisture content falls below 20 per cent. Trees standing in water remain at over 100 per cent moisture content and cannot be ignited with a point source of flame; they will, however, ignite when flame is applied in a ring around the base. Butt immersion was equally effective in reducing hazard for all three species tested: Scots pine, balsam fir, and white spruce. But if the moisture content of the foliage has already dropped below 75 to 85 per cent, the tree will continue to dry even though set in water.