From NFPA.com

This NFPA / UL video demonstrates the flammability of a dry Christmas tree vs. a tree that has been watered regularly.

Facts & figures

• Between 2005-2009, U.S. fire departments responded to an average of 240 home fires that started with Christmas trees per year. These fires caused an average of 13 deaths, 27 injuries, and $16.7 million in direct property damage annually.
• Christmas tree fires are not common, but when they occur, they are likely to be serious. On average, one of every 18 reported fires that began with a Christmas tree resulted in death.
• A heat source too close to the Christmas tree started one of every five (20%) of these fires.
• Eighteen percent of home Christmas tree structure fires were intentionally set. Half of the intentional Christmas tree fires occurred in January and may have been related to disposal.

Source: NFPA’s “Home Christmas Tree and Holiday Light Fires” by Marty Aherns, November 2011.

Also see: Fact sheet on Christmas trees and holiday lights (PDF, 51 KB)