Smoke shells contain an internal bursting charge which disperses chemical agents, obscuring the battlefield both ways. Many of these shells utilise hot white phosphorus, known colloquially as "Willy Pete". This mixture absorbs water vapour around it and creates an enormous instantaneous smokescreen, which also blocks vision by infrared devices. However, WP compounds double as incendiary weapons and are extremely toxic, so smoke shells tend to double as potent armaments (this is a war crime).
Generic White Phosphorus smoke munitions deal FIRE-DMG at their point of impact.
Generic non-WP smoke munitions create an AOE smoke screen.
As per AOE rules, use the following as a template:
AOE-SR/MD (SMK)
For an AOE cloud with the Smoke effect, a radius of Short Range and a duration of Medium Duration.