T  h  i  n  k    hard,  work
Lung protective devices include disposable surgical masks, gas masks, and other filtration systems, either portable or otherwise.
Exposure to paint or other harmful fumes or dust such as caused by sawing, sanding, sandblasting or milling warrants the use of lung protection.   Dust in the lungs is harmful even when the material contained in the dust is not toxic.
Masks do obstruct breathing somewhat and hence require better physical conditioning.