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Engineering LaboratoryFire Research Division

## National Fire Research Laboratory

-  Holiday Fire Safety  Expand or Collapse    -  What Does Fire "Size" Mean? 
  -  NIST Fire Computational Tools 

# What Does Fire "Size" Mean?

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Due to their high surface area to volume ratio and relatively large mass, dry Christmas tree fires can ignite and grow quickly to release large amounts of heat. Table 1 presents representative peak heat release rates (during unconfined burning) of several items that can be found at home.

Fire ‘size’ is measured in terms of the fire’s Heat Release Rate (HRR) in kilowatts  (kW). As shown in the video below, fire development can be described by changes in HRR versus time as a fire burns. After ignition, typical fire development under well-ventilated conditions (where there is sufficient oxygen for the fuel to be completely burned) occurs in three stages:

**Growth**: When fire size (HRR) increases as more flammable material becomes involved in the fire

**Fully Developed:**When fire size (HRR) remains approximately constant (steady burning)

**Decay:**When fire size (HRR) decreases as the fuel burns out or the fire is extinguished
**Video:**
Fire development is a function of many factors including: fuel properties and quantity, room ventilation and geometry (volume and ceiling height), location of fire, and ambient conditions (e.g. temperature, availability of fresh air).

You can compare data in the video above to previous experimental measurements[5, 6] and detailed simulations(link is external)[7] of Christmas tree burning behavior. Detailed descriptions of several key terms – e.g. temperature, heat, flashover, and heat release rate – presented on this page are available at the NIST Fire Dynamics page:  https://www.nist.gov/fire-dynamics.

______________________________
http://codesonline.nfpa.org
[5]
Scotch Pine Christmas Tree Fire Tests
https://www.nist.gov/publications/scotch-pine-christmas-tree-fire-tests-report-test-fr-4010

[6]*Madrzykowski, D., “Impact of a Residential Sprinkler on the Heat Release Rate of a Christmas Tree Fire,” NISTIR 7506, National Institute of Standards and Technology. May, 2008.  https://www.nist.gov/publications/impact-residential-sprinkler-heat-release-rate-christmas-tree-fire*[7]  Mell, W., Maranghides, A., McDermott, R., Manzello, S.L., “Numerical Simulation and Experiments of Burning Douglas Fir Trees,” Combustion and Flame 156: 2023-2041. 2009. https://www.firescience.gov/projects/07-1-5-08/project/07-1-5-08_Mell_exp_sim_doug_fir_cf09.pdf  Downloaded November 1, 2017.

FireFire detectionFire fightingFire modelingFire risk reductionMaterials flammability

## Contacts

                -  Isaac Leventon  isaac.leventon@nist.gov      (301) 975-6887   

-  **‹** Holiday Fire Safety 
-  NIST Fire Computational Tools **›** 

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