Basics

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
CAPR is a powered Controlled-Air Purifying Respirator, without hoses.

Usage

Hood and hose are discarded after each use - [1]
PAPR and general PPE protocols - [2]
Used often in low Biosaftey Levels
Also useful for welding with large amounts of flux in non well ventilated spaces etc