As to the question of rules regarding when and where peaceful protests may be held, that's highly dependent on the specific location of the protest.
The venturi mask, also known as an air-entrainment mask (and sometimes by the brand name VentimaskÂ®), is a medical device to deliver a known oxygen concentration to patients on controlled oxygen therapy.
Some gas masks are also respirators, though the word gas mask is often used to refer to military equipment (e.g. field protective mask). The user of the gas mask is not protected from gas that the skin can absorb. Most gas mask filters will last around 24 hours in a nuclear biological chemical (NBC) situation.