The challenge here is enjoy human control over fire in a manner that is safe, legal and unobtrusive. The obvious and first intended way to do this is to smoke a cigarette. Do so without anyone complaining, glaring, sniffing ostentatiously, or otherwise expressing disapproval and you have earned the achievement.
That means of gaining the achievement is unavailable to anyone who has not attained the legal age to smoke in the geohash jurisdiction, because obviously you can't have a legal cigarette if you're not of legal age to do so, but smoke emanates from fires of all sorts and you can gain this award from a campfire or even a smoky candle. Setting your shirt on fire would not qualify, as it violates the principle of safety.