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What goes into a decontamination unit?

A decontamination unit has a significant number of component parts, divided up into the three key compartments plus functional services.

decontamination unit layout

Clean Compartment

  1. Entry / Exit door to outside – clearly marked “CLEAN” on the outside.
  2. 1 x locker per person
  3. Seating
  4. RPE battery charging point
  5. Clothes hanging hooks
  6. Mirror
  7. High level ventilation from outside with closable louvre
  8. Low level vent to shower compartment
  9. Self-closing door to shower compartment
  10. Space heating
  11. Electric Lighting
  12. Readily cleanable impervious surfaces for walls, ceiling, floor.


Shower Compartment

  1. Thermostatically regulated shower (permitted ratio: 4 users per shower point – not all at once!)
  2. Hanging hooks or rails for RPE and towels
  3. Body wash/shampoo  – note: bar soap is not recommended as it will prematurely block waste-water filtration systems, especially in hard-water areas.
  4. Low-level vents / louvers from clean compartment.
  5. High level vents exiting to dirty compartment.
  6. Two self-closing doors, one to clean compartment and one to dirty compartment.
  7. Sink for handwash.
  8. Electric lighting.
  9. Readily cleanable impervious surfaces for walls, ceiling, floor


Dirty Compartment

  1. Low level HEPA grade air filtration/extract unit, marked as compliant to either PAS60 or BS8520, and supplied with filtration test certificate
  2. High level ventilation from the shower compartment, equipped with non-return flaps
  3. Seating
  4. Clothes hanging hooks
  5. Self-closing door to shower compartment
  6. Self-closing Entry / Exit door to work area clearly marked “DIRTY” on the outside.
  7. Electric lighting
  8. Readily cleanable impervious surfaces for walls, ceiling, floor

nternal view of decontamination shower unit

Functional services for decontamination units

  1. Water heater delivering hot water to the shower (if LPG then room-sealed balanced-flue water heater complete with GasSafe certificate)
  2. Electrical circuits protected by 30mA RCCD
  3. Waste water filtration (dependant on application)


Decontamination Unit waste water filtration

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.

Decontamination unit waste water filtration

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!

How does decontamination unit air filtration work?

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.

Dust filtration unit inside 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).


How to use a decontamination unit

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.

Compartments wtihin a decontamination unit

Upon return, the procedure is as follows (modified according to specific hazards being addressed):

  1. Proceed to the door that accesses the “Dirty Compartment”.  Where appropriate, clean footwear at the bootwash station before entering the “Dirty Compartment”.
  2. After entering the “Dirty Compartment”, ensure that the HEPA filtration unit is operating (to clean the air) and then remove disposable outerwear PPE (if worn, RPE usually remains on and in use at this stage).   Place PPE and footwear in plastic bags and seal for re-use/cleaning/or disposal, as appropriate to your work protocols.
  3. Proceed to the shower compartment, wearing disposable underwear and RPE (if using).   If using RPE then the shower needs to be done before removing RPE. If using powered RPE, hang the battery pack from the wall hooks/rails provided.  Shower thoroughly, ensuring hair and the whole body is thoroughly soaked, washed and rinsed.
  4. Re-usable RPE should be thoroughly cleaned in the shower, or placed in plastic bags and sealed when leaving the shower.  Single-use RPE should be sealed in bags for disposal when leaving the shower.  Any towels used in the shower compartment should be sealed in bags for disposal when leaving the shower.
  5. On completion of showering proceed to the “Clean Compartment”.  Where required, clean towels should be used for drying off in the clean compartment (do not carry forward towels already used in the shower for further use in the clean compartment).  Personnel should dress in clean uncontaminated clothing and footwear.
  6. Finally, exit the DCU through the external “Clean End” door.


How do I set up a trailer Decontamination Unit?

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.

Power buttons for decontamination unit

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:

  • “Standard” decontamination units: don’t carry water or on-board generators – they require continuous connection to on-site services of electricity and water.  When using trailers with an integral LPG water heater, a 13Amp 240v electricity supply is usually sufficient, together with a mains pressure water supply.
  • “Electric” decontamination units: some industrial sites don’t allow LPG or naked flames; in these instances electric water heating is usually selected, which requires a lot of electrical power – typically 63A at 240v for a unit with two showers!


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