Fire extinguishers were devices used to put out fires. In some situations they could also be used as makeshift weapons.
Early evidence of fire extinguishers on board the TARDIS was seen when Nyssa had to contain the fire caused by her sonic destruction of the Terileptil android. A small model usable by a single hand was kept in a wicker basket just outside her bedroom. (TV: The Visitation)
The Eighth Doctor later used a fire extinguisher in the TARDIS library when a page from his copy of The Strand caught on fire, (PROSE: The Bodysnatchers) and the Tenth and Eleventh Doctors sprayed an extinguisher into the console room after particularly rough landings. (TV: The Runaway Bride, The Angels Take Manhattan)
The Doctor's UNIT laboratory was also equipped with fire extinguishers. Upon her first meeting with the Doctor, Jo Grant used one when she saw smoke emanating from one of the Doctor's experiments. The Doctor berated her for this as she had ruined his work. (TV: Terror of the Autons)
Fire extinguishers could be used more offensively, however. The First Doctor, for instance, used a fire extinguisher against a dragon which lived in the forest outside the Pied Piper's castle. (COMIC: Challenge of the Piper) Ben and Polly used adapted fire extinguishers to spray Cybermen with a chemical cocktail designed to kill them. (TV: The Moonbase) On a parallel Earth, the Third Doctor, Greg Sutton and the Brigade Leader used fire extinguishers against the Primords. (TV: Inferno) Back the prime Earth, the Eighth Doctor sprayed the Master with a fire extinguisher, blinding him long enough for him and Grace Holloway to escape. (TV: Doctor Who), while the Ninth Doctor once found that members of the Slitheen family were briefly stunned by the chemicals in an ordinary British fire extinguisher. (TV: World War Three) Likewise, Clyde Langer and Rani Chandra used fire extinguishers to temporarily disable nanoforms. (TV: Prisoner of the Judoon)
Other species were perhaps more susceptible to the effects of fire extinguishers. Clockwork Droids, Silurians, and people like Harvey who had been converted by the Daleks, could all be rendered inactive for several hours by the use of an ordinary fire extinguisher. (TV: The Girl in the Fireplace, The Hungry Earth, Asylum of the Daleks)
Sometimes, however, fire extinguishers proved ineffective weapons. Sarah Jane Smith first sprayed Odd Bob the Clown with a fire extinguisher, then hit him with it, but neither action had any effect. (TV: The Day of the Clown)
In some situations, extinguishers were used more as projectiles – objects to be simply lobbed at a problem. When Brian Hughes locked the doors of the Pinehill Crest Hotel, for instance, Ace tried throwing a fire extinguisher to break them, only to find that they were made of safety glass. (AUDIO: The Shadow of the Scourge)