Controlled, Filtration Engineering Ltd, Air Filtration, Air Quality Control Systems, UK

Controlled Environments (for specific food product contamination control)

Airborne contamination control of a specific, usually high risk, food manufacturing process is based on the use of a controlled or mini environment, where a processing space is put under positive or laminar flow conditions (uni-directional airflow). The application of laminar flow air is a very effective way of controlling a high risk food manufacturing requirement. Uni-directional air will ensure a "washing effect", which controls air quality levels from diffuser face to product contact. The air movement condition necessary to sustain laminar flow also eliminates ingress of contaminated air.

A clean zone or controlled environment is defined as "a room in which the concentration of airborne particles is controlled and the room contains one or more clean zones which can be allocated a particulate cleanliness class". It is important to remember that a high particulate level in the process space air does not necessarily mean a high microbiological contamination. However, to remove potentially contaminating organisms, a degree of air filtration is required. It is correct to say that a low level of particulate in the air will give rise to a low bug count too.

The principle of control is:

Clean the air to the required level for the manufacturing process.

Blanket the product (and process) with clean air – non-laminar flow / laminar flow.

Use sufficient air volume to eliminate ingress of airborne contamination and maintain process integrity.

Air filtration is only one consideration with regard to the air supply quality once the air has entered the controlled zone. If a food manufacturing process within a controlled environment is to remain uncontaminated it must be protected from all sources of contamination by controlling:

Food ingredients.

Food containers entering the controlled space.

The air quality - by air filtration, air movement and air loss.

Personnel controlling operations. (limited access)

Equipment contamination from outside the controlled area - conveyors etc.

Thus cleaning the air and introducing the air correctly only solves one part of a space contamination control programme. High standards of room air quality and hence low levels of contamination are easier to control using uni-directional or laminar flow type installations. Localised isolation using a mini-environment is a cost-effective method of establishing a high level of contamination control to (say) ISO 5 standard.

Air filtration levels required for controlled environment use are of the high efficiency type and filters tested to BS EN1822 are installed after adequate pre-filtration. The design of an installation will depend on size and location of process and supply air equipment design.

The installation and maintenance of laminar flow air systems is expensive and their application is usually restricted to high risk processes, such as liquid fill machines, some powder drying and meat slicing operations.

For some high risk applications an environment that can be monitored to a recognised standard may be required. The following is a reference guide to the controlled environments (clean zone) standards with BS EN ISO 14644 being the replacement for all others listed below.

Comparison of BS EN ISO 14644, UK & USA Standards for Controlled Environments

Classification Number (N)

BS EN ISO 14644

Maximum Particle Concentration per m3 @ 0.5 micron

BS 5295 (1989)

BS 5295 (Pre-1989 – for reference only)

FED STD 209D

FED STD 209E

ISO 1

ISO 2

ISO 3

M1.5

ISO 4

352

M2.5

ISO 5

3 520

E / F

Class 1

100

M3.5

ISO 6

35 200

G / H

1 000

M4.5

ISO 7

352 000

Class 2

10 000

M5.5

ISO 8

3 520 000

Class 3

100 000

M6.5

ISO 9

35 200 000

The selection of a cleanliness class and the interpretation of particulate test results in the "at rest" and “operational” conditions must be viewed in the light of food safety requirements.

Finally a comment on exhaust systems. Many applications, especially hot process air systems, operate with full outside air input and exhaust through the process equipment or by natural leakage from the controlled space. Recirculation of air is usual for rooms where the risk of contamination is considered low and the air supply system is suitably safe in terms of contamination control. The advantage of recirculation can be a saving in cooling and heating bills, however in some cases the air filtration is more costly to maintain when compared with the use of outside air, due to a high dust level or other contamination from the food process space. Contamination of return air ductwork may be a critical factor in deciding what type of air system to adopt. When the exhaust contains an odour which must be treated, usually to comply with environmental regulations, then an adsorber or combination filter system should be installed. These systems, when designed and operated correctly, are cost effective to run, but maintenance is critical. Physical and chemical adsorption is discussed in some detail in a separate technical note from FEL.

Classification Number (N) BS EN ISO 14644	Maximum Particle Concentration per m3 @ 0.5 micron	BS 5295 (1989)	BS 5295 (Pre-1989 – for reference only)	FED STD 209D	FED STD 209E
ISO 1
ISO 2	4
ISO 3	35	C		1	M1.5
ISO 4	352	D		10	M2.5
ISO 5	3 520	E / F	Class 1	100	M3.5
ISO 6	35 200	G / H		1 000	M4.5
ISO 7	352 000	J	Class 2	10 000	M5.5
ISO 8	3 520 000	K	Class 3	100 000	M6.5
ISO 9	35 200 000	L

Controlled Environments (for specific food product contamination control)