Effects of ammonium sulfate and ammonium phosphate on flammability
Document Type: Report
Author(s): Charles W. George; Aylmer David Blakely
Publication Year: 1972

Cataloging Information

  • ammonium phosphate
  • ammonium sulfate
  • aspen
  • chemical compounds
  • chemistry
  • combustion
  • energy
  • experimental fire
  • fire management planning
  • fire retardants
  • fire suppression
  • flammability
  • fuel management
  • fuel types
  • laboratory experiments
  • needles
  • phosphate
  • Pinus ponderosa
  • ponderosa pine
  • Populus tremuloides
  • rate of spread
  • retardants
  • statistical analysis
  • temperature
  • wind
Record Maintained By:
Record Last Modified: June 1, 2018
FRAMES Record Number: 14088
Tall Timbers Record Number: 7857
TTRS Location Status: In-file
TTRS Abstract Status: Okay, Fair use, Reproduced by permission

This bibliographic record was either created or modified by the Tall Timbers Research Station and Land Conservancy and is provided without charge to promote research and education in Fire Ecology. The E.V. Komarek Fire Ecology Database is the intellectual property of the Tall Timbers Research Station and Land Conservancy.


Ponderosa pine needle and aspen excelsior fuel beds, chosen because they exhibit different chemical fuel characteristics, were treated with various amounts of ammonium sulfate and ammonium phosphate and burned in a wind tunnel under controlled environmental conditions. The rate of fire spread, rate of weight loss (equivalent energy release rate), and the residue were measured to quantify the retardants' effects on flammability. An increase in the amount of either fire retardant chemical caused a reduction in rate of fire spread and rate of weight loss while increasing the amount of residue. However, at all treatment levels, ammonium phosphate was more effective than ammonium sulfate. These two chemicals exhibit their primary difference in their effect on glowing combustion. The rate of weight loss and especially the residue are parameters that quantify glowing combustion. Ammonium phosphate is much more effective in decreasing the rate of weight loss and increasing the residue than is ammonium sulfate, which has little effect on the residue. The superior effectiveness of ammonium phosphate is probably due to the difference in thermal behavior of the two fire retardants; total decomposition of ammonium sulfate occurs prior to 450 C., about 250 C. sooner than ammonium phosphate. Temperatures at the surface of the fuel bed probably are within the range of these total decomposition temperatures. Although ammonium sulfate is effective in retarding flaming combustion, the majority of the chemical may decompose prior to the glowing phase and thus not be available to alter reactions taking place during glowing combustion. The study provides general relationships which can serve as standards for comparing the effects of other basic chemicals or forest fire retardant additives.

Online Link(s):
George, Charles W.; Blakely, Aylmer D. 1972. Effects of ammonium sulfate and ammonium phosphate on flammability. Research Paper INT-RP-121. Ogden, UT: USDA Forest Service, Intermountain Forest and Range Experiment Station. 26 p.