From the same paper:
"Pool fires concern flames developed over horizontal fuel surfaces (as opposed to
wall fires which involve vertical fuel surfaces). Generally, these surfaces have defined boundaries and if a liquid fuel is involved its depth is established through the accumulation of fuel in the prescribed area. If there is no fuel confinement then a spill fire may result, with the fuel layer thickness being determined by the equilibrium of forces affecting the motion of the fluid flow. These fires are often large and shallow, requiring specific considerations. Intensive research has been carried over decades on these subjects, though only a small proportion of the work has looked specifically at
large-scale pool fires."