As a Toa, Vakama was able, with tremendous concentration and willpower, to absorb the fires of a furnace. Right afterward, he needed to unleash the energy in intense blasts of flame from his hands, which left him exhausted.
"Fire" described flames produced by combustion. "Plasma" described hot, shining gas. Toa of Plasma could not produce flame or directly burn objects, but they could create fires by shooting plasma at materials to ignite them. Toa of Fire could not shoot beams of superhot, shining air because their power required combustion. Toa of Plasma could possibly heat solids into plasma. A common plasma attack would create a brightly glowing, cloud-shaped beam with no discernable flames.
Tahu could create fire bursts as well as manipulating existing fire.