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Defra does not operate a Class 1-4 system for quarantine stations/confinement facilities, instead requirements are tailored to specific projects and efforts are made to develop, where possible, containment measures utilising authorisation holders existing facilities.

General design & location

Quarantine stations and confinement facilities must be of suitable design and construction and be appropriately maintained to withstand the normal climatic conditions of the area without compromising containment. The location should also be carefully selected to prevent containment from being compromised, such as by damage from branches from overhanging trees, by flooding or proximity to publicly accessed areas where vandalism could occur. The immediate area around the facility should be maintained to good levels of hygiene by the clearing of wild or cultivated plants, and areas further away from the facility should be surveyed for plants which could act as potential hosts for the specified material or pest(s). Such plants should be removed where possible, when not possible regular monitoring of these plants is required. There should be appropriate security measures to prevent unauthorised entry.


For all quarantine stations/confinement facilities physical isolation of specified material or pest(s) from other plants and organisms is required. This could be achieved using secondary containment within cages or dedicated, distinct compartments within the facility. If the facilities are being shared, all plants, plant pests, or other organisms present within the facility must be treated as specified material or pest(s) and must be handled and disposed of accordingly.  The growing of ornamental plants for decorative purposes is not permitted within confinement facilities.

Wherever possible, the facilities in which the material is to be handled (including waste disposal) should be in relatively close proximity to each other in order to reduce the likelihood of escape during transfer. Facilities used for high-risk work should, wherever possible, be interconnected with no requirements to take specified material out of the confinement facilities.


Where possible entry to a quarantine station/confinement facility should be via an entrance lobby with a vestibule or interlocking door system. This can be effectively achieved by not allowing the two lobby doors to be open at the same time and this is best achieved by the use of an audible/visible alarm system or electronic locking mechanism. All doors should be sealed with appropriate rubber or brush seals and should be self-closing. In some circumstances maintaining the facility at negative pressure can be an effective method of sealing entrance doors without the need for a vestibule. Access should be restricted to authorised personnel by maintaining locked outer doors, but mortice type locks should not be used for this purpose. 


Most quarantine stations/confinement facilities will be required to have permanent flooring, especially those used for containing invertebrate plant pests. Exceptionally, polytunnel facilities may not be required to have a permanent floor depending on the nature of the proposed work (e.g. bonsai authorisations). However, the use of suitable matting or sheeting is required in order to facilitate sweeping and the maintenance of good levels of hygiene. The use of boardwalks or clearly defined pathways should also be considered in order to control dissemination of specified material or pest(s) or any contaminated material. 


Quarantine stations/confinement facilities which are being used to contain specified material or specified pests which are soil or water borne should have a dedicated drainage system which can either be blocked off or connected to an appropriate quarantine treatment tank (e.g. heat treatment or chemical disinfection). Sinks which are purely used for hand washing and have no risk of potential contaminants do not need to be blocked or connected to a quarantine drainage system.

Prevention of run-off is required, a sealed floor, impervious to water should be used in association with waterproof, raised edge benching. In facilities where automatic watering systems are in place, the flow rates should be carefully controlled in order to avoid flooding and, wherever possible, a manual system of watering should be adopted.

Windows and skylights

Where windows or skylights are present in a quarantine station/confinement facility these should be sealed and permanently closed e.g. screwed shut or locked (keys should not be left in locks).

Pressure differentials & air filters

Where it has been identified that passive air-borne dispersal could offer an escape route for the specified material or pest(s) (e.g. mobile invertebrates, air-borne fungal spores or pathogens transmitted through plant pollen) the facility should be maintained at a negative pressure with respect to both connecting facilities and the environment. This means that air is constantly being drawn into the facility and this is generally achieved by manipulating the fans responsible for both drawing in and expelling air from the facility. Air filters of appropriate design and technical specification must be in place at all points of air ingress and exhaust from the confinement facility.

High Efficiency Particulate Absorption (HEPA) filters offer the highest level of containment and should be used whenever possible.  HEPA filters are typically made of fan-folded glass-fibre paper with a filtration efficiency of 99.997% i.e. no more than 3 particles in every 100,000 should escape. HEPA filters are not always required for work with larger authorised organisms, or where there is no risk of air-borne dispersal and in these cases standard filters can be used. In any case, from a containment perspective, the filters in place at the air exhaust from any quarantine station/confinement facility need to be appropriate for preventing the escape of the smallest propagule associated with the authorised material (e.g. fungal and bacterial spores, plant pollen and seeds).  For invertebrate containment it is important that filters are sufficient to prevent the organisms from forcing their way through the weave of the filter (see below).

Standard air filters are categorised into one of 2 groups, with each group having a number of different subclasses:-

  • Group G (coarse dust filters), classes: G1-G4 (EU 1-4)
  • Group F9 (fine dust filters), classes: F5-F9 (EU10 5-9)

The filter sizes and efficiencies are listed in table 2 below. You may come across filters with just MERV standards listed. These are the American standards and are included in the table below. G1 filters represent the most basic standard filter with F9 filters representing the best filtering efficiency below the HEPA standard.

The higher the filtering capacity, the more resistance there will be to air flow. This means that the higher specification filters (e.g. HEPA) tend to be restricted to more specialised applications involving smaller air volumes (e.g. microbiological safety cabinets) and will often be inappropriate for handling large volumes of air.

G3 filters are rated as being 98% efficient at trapping airborne particles 10 mm in diameter.  However, G3 filters are not generally suitable for containing invertebrates (e.g. aphids) which could force themselves through the weave of the filter. G4 filters on the other hand are made from pleated panels and are rated as being over 90% effective at arresting particles of 4mm in diameter as well as being much more effective at containing invertebrates.

An arrestance efficiency down to 4 mm should cover most air-borne propagules we would expect to encounter in licensed organisms. For example, cereal powdery mildew (Erysiphe graminis) has windblown ascospores of 20-23 x 10-13 µm and windblown conidia of 25-40 x 8-10 µm whilst most plant pollens will be greater than 18 µm in diameter. However, bacteria and some ascospores are less than 4 µm in diameter and would therefore require a group F filter.

The table below can be used to work out the minimal filter grade that will be effective for the work being carried out.

In general, positive pressure is not acceptable for containment.  However, in exceptional circumstances a positive pressure facility may be approved if the work exclusively involves pathogens with no risk of airborne dispersal, but where mobile vectors can transmit the organism in question significant measures would need to be in place to ensure they didn’t enter the compartments with plants etc.  e.g. if virus transmission work is carried out using invertebrate vectors then these plants could not be moved into a positive pressure facility.  Further guidance can be provided by Defra.


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