A comparison of the gas-phase fire retardant action of DMMP and Br2 in co-flow diffusion flame extinguishment,‡

Phosphorus-containing compounds are added to polymers as fire retardants and they are believed to act in both the gas and solid phases. In gaseous flame studies, they have been shown to be very effective gas-phase flame inhibitors; however, their performance varies with flame type. In particular, their effectiveness in co-flow diffusion flames is much lower than in other flames. To understand this behavior, co-flow diffusion flame experiments have been performed using dimethyl methylphosphonate (DMMP) added to the fuel stream. CO2 flame extinguishing tests show that phosphorus (via DMMP addition) is much more effective (∼4 times) than bromine (Br2) at low concentrations. At higher concentrations (above ∼5000 µL/L), the efficiency ranking is reversed due to saturation of the DMMP inhibition effect, which is not observed in the case of Br2 addition. The role of particle formation (via condensation of active phosphorus-containing species) in the loss of effectiveness of DMMP is investigated using Rayleigh scattering measurements. In order to understand the behavior of the flame stabilization region that is disrupted during flame extinguishment, premixed burning velocity simulations with detailed kinetics are performed for DMMP or Br2 addition to the flames.