In the steam-assisted flares steam is injected into the combustion zone to promote turbulence and entrain air into the flame. In the air-assisted flares forced air is used to provide the combustion air and mixing; these flares can be used when steam is not available. The non-assisted flares do not have any mechanism for enhancing the air-flame mixing; they are used for gases with a low heat content and a low carbon/hydrogen ratio (such ratio is related to the smoke production). Finally, the pressure-assisted flares use the vent stream pressure to promote mixing between air and flame.