Smoke

Smoke was commonly a product of fires. When combined with fog, it created smog. (PROSE: Amorality Tale)

According to the Third Doctor, steady state micro-welding, pioneered by the Lamadines, created more smoke than it did fire. On first meeting the Doctor, Jo Grant feared that the smoke emanating from his repair work — using steady state micro-welding — meant his "bench was on fire". She tried to put out these imagined flames with a fire extinguisher, much to the Doctor's immediate fury. (TV: Terror of the Autons)

The smell of smoke could be both sweet and pungent. (PROSE: That Which Went Away)

In some cases, smoke filling the lungs could lead to death before the fire itself could deliver any damage. As Freda described it, this was akin to "drowning in smoke". (AUDIO: Asylum)

Smoke could also be beneficial to certain forms of life. As the Ninth Doctor explained, Earth's abundance of smoke and oil (combined with toxins and dioxins in the atmosphere) made for a perfect food source for the Nestene Consciousness. (TV: Rose)

Smoke followed the Ninth Doctor while he exited the boiler room door in C. S.'s school. (PROSE: Have You Seen This Man?)