Coston Flares are consumable items used to reveal a seven-square area. Coston Flares can only be fired six-squares away from your explorer.
The effect of a Coston Flare can be improved by having a Sailor in the expedition.
The flares are stackable to max 20 and a flare is consumed on use. The flares can be used as many times each turn, but there is a small chance for the flare to ignite and cause fires. However, this will only happen if the target field of the flare usage is burnable (and not e.g. mountains, water, desert etc.)