Which of the following is NOT an organic fuel?

The correct answer highlights that coal is not classified as an organic fuel. Organic fuels are generally derived from living organisms or the biological processes that once occurred in them, primarily consisting of carbon, hydrogen, and possibly nitrogen or sulfur as the main components.

While wood is derived from trees, a living organism, and natural gas is composed of hydrocarbons derived from ancient organic materials, coal's formation process is different. Coal is a fossil fuel that has been formed through the geological transformation of ancient plant materials over millions of years under heat and pressure, which effectively changes its chemical structure. Hence, although it originates from organic matter, the transformation into coal classifies it as a fossil fuel rather than an organic fuel in the common sense used in fire investigation.

Plastics, while synthetic and often derived from petrochemicals, do not qualify as organic fuels either, but in the context of this question, coal is the primary focus since it represents fossilized energy rather than a direct biological source. Understanding the distinctions between these fuels is essential for fire investigators to assess fire behavior, potential fuel sources, and their respective combustion properties.