Abstract: In order to analyze the complexity and uncertainty of fire development and smoke spreading in highly humid confined space， a 3.6m × 1.2m × 1.4m experimental model was set up， using a 600mm diameter alcohol pool as the fire source. Experimental ambient temperature was (20±2)℃， while the relative humidity was changed from 30% to 90% with 5% error. Several parameters were measured to analyze the pool fire development under different environmental humidity conditions， including the mass loss rate of fuel， the maximum flame temperature， the average temperature of upper hot smoke layer， the radiant heat from the flame， the radiant heat received by the ground， the O₂ concentration near the flame root and the CO₂ concentration in the smoke. The results showed that when the relative humidity reached about 90%， the mass loss rate of fuel， the maximum flame temperature， the average temperature of the upper hot smoke layer， the radiant heat from the flame and the radiant heat received by the ground decrease significantly. Also， the duration of the developing stage of fire was prolonged， and the temperature dropping gradient in the extinction stage decreases. In conclusion， with a normal temperature and high relative humidity of 90%， the development and spread of pool fire is significantly inhibited.

Key words: alcohol pool fire, relative humidity, radiant heat, flame, smoke