The influence of high altitude on fire detector test fires

We have measured the pressure dependence of fires similar to those of the European standard fires at altitudes above sea level from 400 m (970 mbar) to 3000 m (710 mbar) in a mobile test room of reduced size (6 × 2.8 × 2.1 m). At all altitudes combustible parameters were kept constant. We recorded standard parameters, in particular optical extinction m, the y-value of the standard ionization chamber and increase in temperature ΔT, as well as CO, CO 2 and O 2 concentrations. With decreasing outside pressure fires develop more slowly. Our data show a dependence of burning rates on pressure as ∝p ∝ where a ≈ 1.3. Whereas maxima of ΔT and change of CO 2 concentration show no significant dependence on pressure, maxima of extinction m decrease by α factor of 2.7 ± 0.2 (polyurethane foam fire) or 2.2 ± 0.2 (n-heptane fire) with pressure decreasing from 970 to 710 mbar. At this maximum pressure change, decrease of ‘smoke density’ y is smaller. However, m y ratios remain constant up to an altitude of 1800 m.