SCBA (Self Contained Breathing Apparatus) and Escape Self Rescuers. 
Suitable for confined spaces or emergencies, provides breathable air in an immediately dangerous to life or health atmosphere (IDLH).

SCBA could be open-circuit (vents the used air outwards) or closed-circuit (recycles/filters/reuses air, while supplementing with additional air). They allow access, entry, and work in difficult areas (IDLH contaminated or confined space) without long air hoses to the outside (airline). 

Escape self-rescuers are smaller and lighter, designed only for emergency exit from an area when the atmosphere becomes contaminated.