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16th Dec 2011

Design Considerations When Controlling Air Quality during the Development & Production of Medical Devices

The options, when designing a clean room or controlled environment for use in the Medical Device market, are numerous. This article outlines the advantages and disadvantages of designs, along with recommendations on cost-effectiveness; for development stages, right through to large scale manufacture.

Clean-rooms defined

Medical devices are produced in a cleanroom; an environment where the concentration of airborne particulate is controlled to reduce the risk of product contamination. Cleanroom is a general term which refers to an environment in which particles of dust are controlled. The definition of which is shown in Table I.

Table I: Definition of clean room according to ISO 14644-1, Cleanrooms and associated controlled environments, Part I: Classification of air cleanliness
"A room in which the concentration of airborne particles is controlled, and which is constructed and used in a manner to minimise the introduction, generation and retention of particles inside the room and in which other relevant parameters, for example, temperature, humidity and pressure are controlled as necessary.”

For many industries, including Medical Device Manufacture, where microbial growth could be harmful to the end product, the control of micro-organisms also needs to be controlled. This means that the selection of construction materials and furnishing equipment for a cleanroom need to be carefully selected, to inhibit the growth of such micro-organisms.

The most common method used to control airborne particulate is to introduce clean air to the room through a High Efficiency Particulate Air (HEPA) filter. The fresh intake of filtered air flushes existing contaminated air from the cleanroom through designated outlets. With the modular design of cleanrooms, these outlets run right the way around the bottom of the room to ensure an even airflow and reduce turbulence.

The combination of an introduction of a high volume of additional air, along with restricted air outlets to allow air to exit the room, creates a pressure differential between the internal clean room and external contaminated area. This pressure differential creates a positive airflow which ensures particles cannot re-enter the cleanroom through the air outlets.

By design, the introduction and retention of particles in a cleanroom is therefore controlled. The main source of contamination within a clean area thus occurs through personnel movement and equipment. Procedures to control the generation of particles should then be in place to ensure the cleanliness of a cleanroom is maintained. Such procedures include the selection of correct cleanroom apparel, implementing gowning procedures and the use of appropriate cleanroom furniture.

The classification of a cleanroom is determined by assessing the cleanliness of the air in the room, using defined measures set within the industry standard ISO 14644-1. The most prominent measure being the quantity of particles per cubic metre of air. The ISO 14644-1 clean room classifications range from 1 to 8, with level 1 having the lowest level of particulate, therefore being the cleanest. The most common levels of classification used in the device industry range from ISO Class 5 to ISO Class 8.

Clinical Trials

When producing a new medical device for clinical trials, the environment in which the trial product is produced, needs to replicate the type of environment and level of clean-room classification that would be used in large-scale manufacturing. The trend, therefore, is to use a clean room of modular design, which can offer a high standard of environment, but has the ability to rapidly expand with the growth of manufacturing output. Limited budgets at the development stage for the clean room mean that a modular room offers the required flexibility and can expand from just a few square meters up to over 100 m².

Cleanroom Construction

There are three main types of cleanroom construction; usually termed traditional build, modular and mini-environment. The traditional style of cleanrooms involves fully converting part of an existing building into a cleanroom, whereas modular cleanrooms are freestanding steel frames with HEPA filters installed in the ceiling grid and wall panels to enclose the localised clean area. The mini environment creates an ultra-clean zone within an existing controlled area.

Traditional Build

Traditional designs generally feature a central air-handling unit which re-circulate airflow. The room is constructed from a solid wall or steel, double-skinned partition panel with a sealed non-shedding floor and a grid or panelled ceiling. Lights, ducting and services of air and power can be fitted above the ceiling, or suspended from steel work above the room. Entrance to the room is via a double-entry system to reduce the risk of contaminated air entering the clean room. The design of the clean-room dictates that it has a fixed position and due to the permanency of the structure, further expansion can be disruptive to production.

The complex design of the room makes this the most expensive form of installation and any planned expansion can cause extensive production downtime. Installation time starts at a few weeks, but increase dramatically subject to complexity and size.

The Modular Approach

Modular cleanrooms are more production-friendly and consist of a freestanding steel framework being installed into part of an existing laboratory, cleanroom, factory or warehouse. HEPA filtration in the ceiling and wall panels then create an enclosed and localised clean area. They can be installed around existing machinery and typically have a lead time of just a few weeks. They are generally installed in under a week due to the simplicity of their design and have a lower cost per square metre than a traditional build.

The steel framework is typically constructed from aluminium or mild steel which is powder-coated to give a hygienic finish. Aluminium is generally chosen for it's resistance to corrosion, but tends not to be as sturdy as the robust mild steel frames, which are also corrosive-resistant.

Although modular cleanrooms are robust and solid structures which are used as permanent contamination control solutions, their simple construction and independence from the surrounding building means they have the flexibility to be mobile, relocated, or expanded as demand increases.

Modular designs typically feature single-pass airflow and construction usually consists of the frame being enclosed with side walls constructed of either clear strips of PVC that are overlapped to create a barrier (softwall), or clear PeTG solid wall panels (hardwall). In both situations wall panels are usually clear to allow external light to penetrate the cleanroom and illuminate processes.

Air handling is introduced through a single or a series of filter fan units (FFUs) that pull air through a prefilter then force it through a HEPA filter. Although clear ceiling panels are generally used, the modular rooms may require additional cleanroom lighting, depending on the ratio of FFUs within the ceiling.

These rooms can be mounted on castors, which allow them to be used in various areas or fixed in a single position over a work area or piece of equipment. Their versatile construction materials and modular design allow rapid installation. Some suppliers can offer delivery within a week. The modular design significantly reduces disruption when expanding the area. The installation time tends to be 5% that of the time taken to install a traditional build cleanroom. The simplicity of the design also helps to keep capital costs low, approximately 30–50% less than those for a hard-wall construction.

The disadvantage of the softwall modular cleanroom design means it is not suited to being positioned near external doors, because strong draughts can disrupt the integrity of the softwall curtains. The hardwall modular cleanroom is therefore better suited in some circumstances and proves to be exceedingly popular due to its durability despite costing more than its softwall counterpart. This is due to its pleasing visual effect and the ability to feature bespoke customer branding. Hardwall cleanrooms tend to use the softwall strip curtains for access and ease of product transfer.

Mini Environment

Mini-environment design takes a specific view of the area that needs to be controlled. It is most commonly used to create an exceptionally clean environment within an existing cleanroom. As the filters are pulling through filtered air, high levels of classification can be achieved - from ISO Class 5 to 1. By only dealing with a small area, costs can be kept relatively low considering the high classification which can be achieved. Typically, a mini environment is a small modular cleanroom placed within either a traditional build or modular clean-room/area. As the mini-environment is surrounded by a clean area, there is therefore a significant reduction in the risk of contamination when introducing or removing product from the cleaner zone.

Filtration Advancements

One of the major technological advancements that has helped to produce the modular clean room is the improved design of the Fan Filter Unit. The combined sealed unit incorporates prefiltration, a motorised fan and a HEPA filter. The low-profile design with integral power and control features enable these units to be added to an existing room without having to alter any previous installation.
These advancements allow a company or individual to develop medical devices within a classified clean-room area for a budget of less than £10,000. A modular cleanroom can then be installed within premises without altering the fabrication of the building and prevents a company from breaching any lease restrictions. As demand grows on the clean room and the need arises to expand the room or relocate the clean room to new premises, this can be achieved without losing the initial investment.


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