Basics

The formal name is "CAPR" or Controlled-Air Purifying Respirator
A Device Mainly Used as a filtered/safe air supply in enviroments where there IS oxygen, and the user can breath normally (as in lung function isn't impaired), but a chemical/biological/particulate hazard exists/is expected
Is essentially a forced air filter, with a hose leading to a mask
Typically is a belt with the power/controls/filter, then a tube to a mask/hood
A Similar "box" can feed a Positive Pressure Personnel Suit , a type of hazmat suit for bio uses (ie doesn't protect against heat (like firefighting "bunker suits" , or from certain liquids and/or radiation like other Hazmat suits

Usage

Hood and hose are discarded after each use - [1]
PAPR and general PPE protocols - [2]
Used in Biosaftey Levels 3 and 4 (Medical, Bioscience, etc)
Also useful for welding with large amounts of flux in non well ventilated spaces etc