A range of different types exist, dust masks, half mask respirators, full face mask respirators and powered (fan assisted) respirators. These use filters to remove the contaminants in the workplace air. In a negative pressure device one or more air purifying filters are attached via an inhalation valve to a tight fitting face piece. The negative pressure relative to the ambient air outside the respirator is created by inhalation of air drawing the contaminated air through the purifying filter