Commonly referred to as “extract units” or “dust filtration units” (DFU), the air filtration system is fitted in the “Dirty” compartment of a decontamination unit. When the decontamination unit is in use the DFU creates a negative pressure and unidirectional air-flow within the three compartments by extracting air from the dirty compartment, drawing it through a very fine filter (HEPA filter), and discharging the “cleaned” air outside the decontamination unit.
The negative pressure achieved, and the arrangement of self-closing doors, ventilation louvers, and non-return vents, ensures that the three chambers of the decontamination unit are continuously purged with outside make-up air moving uni-directionally from the clean compartment, through the shower, to the dirty compartment. Airborne particulate matter shed from the operatives Personal Protective Equipment (PPE) is carried on the airstream to the DFU.
The standard of filtration is extremely high – the DFU extract system is required to be regularly tested and certified to validate that it is removing at least 99.995% of the particulate matter down to 0.3 micron in size (to put that in perspective, 1000 microns = 1 mm, so we are talking about removing 99.995% of particles that are 1/3000th of a millimetre in size!). Always ask for a copy of the test certificate.
The DFU must be equipped with a monitoring device to indicate filter condition (usually a manometer), and must be fitted with non-return flaps on the discharge side of the DFU (usually gravity operated or spring assisted).