A decontamination unit has a significant number of component parts, divided up into the three key compartments plus functional services.
Once the decontamination unit has cleaned the operatives, there remains the issue of what happens with the dirty water and how “grey water” (shower wash water) is disposed of depends on what your operatives may have been exposed to and on the regulations appropriate to your work activity, on local byelaws, and what the water authority is willing to accept!
The most common filtration systems remove particulate matter from waste water utilising a single-pass cartridge filter, which is disposed of after use; this is normally in operation in conjunction with a pump to ensure adequate flow rates. Single cartridges are sufficient for most applications, but multiple cartridge systems are available for heavy loadings.
Filtering particulate matter down to 5 micron is common. However, filters are available down to 1 micron and below if required, although the penalty here is that higher pump pressures are required to maintain flow, or larger banks of filters must be used.
It’s important to recognise that soluble (dissolved) matter won’t be removed by physical filtration. If you need to remove dissolved matter then you may need to consider specialist chemical filtration methods / use of activated carbon filters – which is a design world in its own right!
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).
A typical decontamination unit (DCU) has separate access doors clearly marked “Clean” and “Dirty” which allow access to the three internal compartments. At the start of the work period the operative should enter through the “Clean” door and change into coveralls, footwear and Personal Protective Equipment (PPE) appropriate to the hazard they may encounter, including (if necessary) Respiratory Protective Equipment (RPE).
Once dressed they should proceed through the “Shower compartment”, into the “Dirty compartment”, and then exit the trailer through the external door along the route to the work area.
Upon return, the procedure is as follows (modified according to specific hazards being addressed):
Single-axle trailer versions are the easiest to manoeuvre and they are usually quite lightweight – most twin shower units weigh between 900kg and 1500kg. Once sited, apply the handbrake, wind down the stabilising legs, and level the unit.
“Self-Contained” decontamination units carry their own water supply and on-board generator. Turn on the LPG water-heater, switch on the generator, and connect the waste-water filtration system between the trailer and the waste disposal point.
Then turn on the internal lighting, space heating, negative pressure air filtration system (NPU), and shower & waste pumps. You’re now ready to use the decontamination unit.
It’s worth knowing about two variations of the above: