In order to protect your lungs and respiratory system, you must control what comes into your body through the atmosphere. A breathing mask will help you do that. You need to wear one if you work around toxic chemicals or dangerous fumes. Work environments that have inadequate ventilation and those that feature flying particles such as dust debris are also good reasons to wear a breathing mask.
Breathing masks are among a class of personal protective equipment known as Respiratory Protective Equipment (RPE). The class also includes respirators. An RPE may come with some form of face piece, such as a helmet, visor, hood or mask. Before using RPE, you should take all reasonable steps to control the exposure and improve the quality of the air, and ventilation at your place of work.
Hoods, helmets, visors and blouses are all loose fitting types of face protection. They are not suitable for people with facial hair, or those who wear glasses. These types of face pieces rely on a suitable and sustained supply of clean air being delivered to them in order to prevent contaminant leakage. These types of RPE are only used on fan powered respirators and air-fed breathing apparatus.