What fuel group has the highest surface area to volume ratio?

The fuel group with the highest surface area to volume ratio is grass. Grass fuels consist of fine, light materials with a high proportion of their mass in relation to their surface area. This characteristic allows them to ignite quickly and burn rapidly because more surface area is available for combustion relative to the amount of fuel.

In contrast, shrubs, timber, and logging slash have lower surface area to volume ratios. Shrubs tend to have thicker stems and denser foliage, which reduces the surface area available for ignition compared to grasses. Timber and logging slash, being larger in size with more bulk, similarly result in a lower ratio, making them less conducive to rapid ignition and combustion in comparison to grass. Thus, grass is the most effective in terms of quick ignition and fire spread due to its available surface area for burning.