FPEeXTRA Issue 71

The UMD Christmas Tree Fire Size Prediction Competition: An annual event to promote awareness, education, and collaboration in the fire safety science community

By: Isaac T. Leventon, PhD

According to National Fire Protection Association (NFPA) statistics, between 2014 and 2018, fire departments in the United States responded to an average of 160 home structure fires each year that began with Christmas trees {Ahrens, 2020}. These fires caused an annual average of two civilian deaths, 14 civilian injuries, and $10.3 million in direct property damage. Although these events represent a small fraction of fires reported each year {Ahrens, 2020} these fires are particularly challenging to life safety. Based on data collected between 2011 and 2015 {Ahrens, 2017}, when Christmas trees were the first item ignited in home structure fires, one out of every 32 reported fire events resulted in a death, compared to an average of one death per 143 total reported home fires (a factor of 4.4x increase in mortality).

The American Christmas Tree Association reports that nearly 94 million households had at least one Christmas tree in 2020, of which 15 percent were natural (vs. artificial trees) {ACTA, 2020}; however, a recent NFPA report {Ahrens, 2020} suggests that fires involving natural trees are nonetheless approximately twice as common as those involving artificial trees. Many of these fire events occur later in the season {Ahrens, 2020; Ahrens, 2017; NFPA, 2013}, potentially because the longer a natural tree is kept, the more likely it is to dry out, which can increase the potential for ignition, faster fire growth, and larger peak fire size {Ahrens, 2017; Ahrens, 2017, ATF, 2015; Stroup et al., 1999; Hoehler et al., 2020} (see Video 1).



Each year since 2014, the Department of Fire Protection Engineering at the University of Maryland (UMD) has conducted a series of full-scale experiments to demonstrate the potential fire risk of dry Christmas Trees. The event is regularly covered by local and national media (Fig. 1) and the experiments also provide a valuable learning experience for students of the Department. In its early years, the event served as the finale for an introductory fire science program taught at UMD (this program was supported in 2014 and 2017 by grants from the SFPE Scientific and Educational Foundation). More recently, senior- and graduate-level students of the Department have been invited to experience (from a safe distance) these large fire experiments to contextualize the fire behaviors that they learn to calculate in courses such as Fire Dynamics (ENFP 415) or Enclosure Fire Modeling (ENFP 425).


Figure 1. Media coverage of Christmas tree fire safety demos in 2014.

Yearly experiments always include the full-scale burning of well-watered trees and those that have been allowed to dry for approximately two weeks. In different years, additional tests have also explored the impact of residential sprinklers on tree burning behavior, bench-scale burning of artificial tree branches, and, in 2019, as part of a collaborative effort between researchers at the National Institute of Standards of Technology (NIST), a series of 14 experiments was conducted at UMD to characterize firebrand generation during the burning of full-scale vegetation in the absence of ambient wind (it has been shown that firebrands can have a significant impact on the spread of wildfires{Manzello et al., 2020}). Measurement data from the 2019 experiments include: time-resolved mass loss rate during burning, heat flux at a distance, and total mass of firebrands generated during burning. Further analysis of more than 10,000 firebrand collected during these experiments provided insight regarding the size, mass, and shape distributions of these firebrands, measured firebrand yields (i.e., mass of firebrands generated per mass of tree burned) and the dependence of each of these quantities on tree moisture content and species.

The Competition

Figure2.jpgThe measurement data collected each year during these experiments has also been used to enable a friendly competition that encourages communication and collaboration between members of the fire safety science community. Beginning in 2014 as a small event drawing just a dozen participants exclusively from UMD, more than 100 individual predictions have been submitted to recent competitions, with the 2020 event drawing submissions from 34 unique institutions across 16 countries (including 10 different states in the US). For this competition, students, faculty, researchers, and engineers from fire safety programs around the world are invited to predict the burning behavior – i.e., time-resolved fire size (heat release rate, HRR) – of a dry Christmas Tree and the highest individual and highest group scores are announced, with the research team that has the highest average group score earning the coveted Golden Pinecone (Fig. 2).

Although this competition is meant to be a fun event for the community (and to share an important holiday fire safety message), it also offers a teachable moment: experimental measurements have an inherent uncertainty and our ability to accurately predict fire behavior should always be assessed with explicit considerations for this uncertainty. In short, this means that predictions are scored with respect to the average and standard deviations (with explicit considerations for measurement uncertainty) of the burning behavior (i.e., peak HRR, time to peak HRR, fire growth time and duration, and total energy release) measured in repeated experiments.

This year’s competition will take place on Thursday, December 16, 2021; the submission (and generation of) predicted HRR curves is made possible by visiting: https://pages.nist.gov/christmas_tree_fire_safety/. Further details about this competition can be found at: https://fpe.umd.edu/events/christmas-fire-safety-demo.

Christmas Tree Fire Safety Tips

If you plan on keeping a natural Christmas Tree this season, please keep it healthy, well-watered, and away from potential ignition sources. The National Fire Protection Association (NFPA) suggests several additional steps that you can take to reduce the risk of a Christmas Tree fire in your home {NFPA, 2020}:

  • Choose a tree with fresh, green needles that do not fall off when touched.
  • Before placing a tree in its stand, cut 5 cm (2 in.) from the base of the trunk.
  • Add water to the tree stand. Be sure to add water daily.
  • Make sure that the tree is at least three feet away from any heat source (e.g., space heaters, candles, fireplaces, heat vents, or lights).
  • Make sure that the tree does not block an exit.
  • Use lights that are listed by a qualified testing laboratory. Replace any string of lights with worn or broken cords or loose bulb connections.
  • Always turn off tree lights before leaving home or going to bed.
  • Never use lit candles to decorate the tree.
  • Get rid of the tree after Christmas or when it is dry and keep it away from your home/garage.
  • Check with your local community to find a recycling program.

Isaac T. Leventon, PhD is with NIST


Ahrens, M., “Home Structure Fires Involving Christmas Trees,” NFPA Research. (2017)

Ahrens, M., Maheshwari, R., “Christmas Tree Fires,” NFPA Research. (2020)

American Christmas Tree Association (ACTA), “Ninety-four Million U.S. Households Will Celebrate The Holidays With At Least One Christmas Tree,” from November 2020 Nielsen English Language PanelViews Survey. Accessed September 27, 2021.

Bureau of Alcohol, Tobacco, Firearms and Explosives, “Executive Summary: Fire at 936 Childs Point Road”, ATF Investigation #761010-15-0026. (2015)

Hoehler, M. S., Bundy, M. F., DeLauter, L. A., Gerskovic, L., Garcia, J. R., “Fire Hazards of Dry Versus Watered Christmas Trees,” NIST Technical Note 2131. (2020)

Manzello, S. L., Suzuki, S., Gollner, M. J., & Fernandez-Pello, A. C. (2020). Role of firebrand combustion in large outdoor fire spread. Progress in energy and combustion science, 76. (2020)

NFPA, “Christmas Tree Safety” Available: https://www.nfpa.org/-/media/Files/Public-Education/Resources/Safety-tip-sheets/ChristmasTreeSafetyTips.ashx (2020). Accessed September 27, 2021.

NFPA Fire Analysis & Research Division, “NFPA Christmas Tree Fact sheet,”. http://www.nfpa.org/news-and-research/fire-statistics-and-reports/fire-statistics/fire-causes/holiday/christmas-tree-and-holiday-lights. (2013). Downloaded December 7, 2014.

Stroup, D. W., Delauter, L., Lee, J., Roadarmel, G., “Scotch Pine Christmas Tree  Fire Tests - Report of Test 4010,” Available: https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=907753  (1999)