Steel flare stack types are classified as horizontal, elevated, or slanted as well as single point or multipoint burners. The flared stream mediums and phases that exist are: vapor, liquid or liquid vapor mixtures. Before a flare type is selected, it is important to understand the environmental impacts, process requirements and economic considerations of a particular operation or project. Improper application of a steel flare stack technology can lead to not only poor performance, but also negative environmental impacts.
Horizontal – horizontal flares utilize burners which release into pits to retain liquids discharged with gases. For liquid and vapor mixtures, a horizontal flare is appropriate.
Elevated – flares fire vertically from a point higher than any other equipment and are ideal for gaseous streams.
Slanted – typically utilized to achieve low radiation, noise, and space requirements at production platforms.
Single Point – a steel flare stack that has an exposed pipe with only one exit point. Single-point flares can be smokeless or non-smokeless using air-assisted or steam-assisted designs and are suitable for low-pressure applications. 
Multipoint – recognized as being better for the environment due to staging features which boost combustion and create smokeless burning. A steel flare stack that has several exit points and is designed for higher pressure applications. These can be located on the ground level or at an altitude using boom supports. 
- “Flare Selection for the Chemical Process Industries”