Atmospheric density jacket

An atmospheric density jacket, or ADJ, was a garment worn to protect the wearer against thin atmospheres. It had been invented by the First Doctor in case an accident on board the TARDIS accidentally deprived him of sufficient air. He wore an ADJ on his first two visits to Vortis. (DWAN: The Lost Ones, DWAN: The Lair of Zarbi Supremo)

The Doctor required Ian to don an ADJ when they first began exploring Vortis.

A key feature of an ADJ was the resipiratory compensator affixed to its breast. Ian likened the compensator to an "advanced oxygen mask". (DW: "The Web Planet") The effective life of an ADJ was only about an hour, after which it had to be recharged. (DW: "The Zarbi")