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.
Types of Gas Masks - Gas mask types include half-mask air-purifying respirators and full-face respirators. Find out how each of the different types of gas masks work.