To investigate the effect of low air pressure on the combustion characteristics and puffing flame frequency of pool fires, ethanol and n-heptane pool fires were performed using 15 square burners of various size in both Lhasa (altitude: 3650 m; air pressure: 65 kPa) and Hefei (altitude: 24 m, air pressure: 100.8 kPa) fire laboratories. Comparison of the experimental results for pool fires of the same size in the two places shows that, firstly, the maximum rise in the centerline temperature in flames in Lhasa is generally larger than that in Hefei. Secondly, the dependence of the burning rate exponent n ((m) over dot '' proportional to p(n)) on the air pressure varies with the equivalent diameter D of the burner, with n < 0 (D < 7 cm), (0-1) (7 cm < D < 10 cm), (1-1.45) (10 cm < D < 19 cm) and 1 (D > 19 cm). Thirdly, radiation fraction of the pool fire flames is smaller at low air pressure. Finally, the puffing frequency of the pool fire flames is higher at low air pressure. Compared with Hefei, in Lhasa, for the same size burner, a higher maximum temperature together with less radiation from the flame is observed. This shows that in low air pressure, the pool fire is more buoyant, which leads to stronger periodic oscillation and a higher flame puffing frequency. (C) 2011 Elsevier Ltd. All rights reserved.