The effect of accidental fires are simulated to understand the response of items such as vehicles, fuel tanks, and military ordnance and to remediate the effects through re-design of the items or changes in operational procedures. The comparative combustion emissions of using jet propellant (JP-5) liquid fuel pools or a propane manifold grid to simulate the effects of accidental fires was investigated. A helium-filled tethered aerostat was used to maneuver an instrument package into the open fire plumes to measure CO, CO2, fine particulate matter (PM2.5), polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), and elemental/organic/total carbon (EC/OC/TC). The results showed that all emissions except CO2 were significantly higher from JP-5 burns than from propane. The major portion of the PM mass from fires of both fuels was less than 1 μm in diameter and differed in carbon content. The PM2.5 emission factor from JP-5 burns (129 ± 23 g/kg Fuelc) was approximately 150 times higher than the PM2.5 emission factor from propane burns (0.89 ± 0.21 g/kg Fuelc). The PAH emissions as well as some VOCs were more than one hundred times higher for the JP-5 burns than the propane burns. Using the propane test method to study flammability responses, the environmental impact of PM2.5, PAHs, and VOCs would be reduced by 2300, 700, and 100 times per test, respectively.