What Is the Limit for Alcohol Explosion Concentration

The lower explosive limit (LEL) of alcohol is 3.5%, and the upper explosive limit (UEL) is 18.0%.

Explosions only occur between these two limits. Above the UEL, the air is insufficient; flames may burn but cannot spread or cause an explosion. Below the LEL, the concentration of combustibles is too low. Excessive air cools down the environment, preventing flame propagation and thereby averting explosions or ignitions.