Humidity plays a huge role in ignition as well. Roughly 8% Humidity for a cigarette cherry to ignite in dry grass or leaves as I remember. They're already arresting arsonists on the pacific west coast. They tend to toss lit bbq briquettes out a car window, or toss a road flare while driving by according to arrest reports. You are correct that unless it is a pile of green straw, grass, or manure, or improperly stored chemicals, spontaneous combustion is often not likely.
Humidity plays a huge role in ignition as well. Roughly 8% Humidity for a cigarette cherry to ignite in dry grass or leaves as I remember. They're already arresting arsonists on the pacific west coast. They tend to toss lit bbq briquettes out a car window, or toss a road flare while driving by according to arrest reports. You are correct that unless it is a pile of green straw, grass, or manure, or improperly stored chemicals, spontaneous combustion is often not likely.