Feature Article

By: J. Govier,
Connect 2 Cleanrooms Ltd, Kirkby Lonsdale, UK

Cleanrooms are essential elements of medical device production: they reduce the risk of particles, which may carry harmful micro-organisms, entering and being retained in the production environment. Traditional cleanrooms tend to consume large amounts of energy, produce large quantities of landfill waste and use toxic cleaning products with the associated environmental consequences. Ways to reduce this while remaining compliant with the relevant standards have been investigated. The results are reported here and can be summarised in four main recommendations:

The standard industry approach to controlling the concentration of airborne particles within a given area, that is, a cleanroom, currently consists of “supplying it with exceptionally large quantities of air that has been filtered with high efficiency filters.”¹ Although this is undoubtedly an effective method, by taking a more scientific approach it is possible to achieve the same, or better, results with a reduced carbon footprint.

 

By supplying only the minimum quantity of filtered air that is required to dilute the concentration of particles in the room to the target level (for example, by using an electronic speed controller), power consumption of the fan units can be significantly reduced. Tests conducted to determine the power required to produce various airflows show the following, note that the filter contained in the test unit was new (Figure 1).

 

A fan unit that consumes 470 W at full power and producing an airflow of 80 cm/s, only requires 220 W to produce 50 cm/s. In terms of the carbon dioxide (CO₂) produced in generating the electricity consumed, this represents a saving of 268.5 kg of CO₂ annually per fan unit.² Although some practitioners argue that reducing airflow risks failing to achieve a notional “required” number of air changes per hour, the relevant standard, ISO 14644,³ does not specify such a requirement. Hence, provided the reduced fan power has been calculated and validated to maintain the specified target particle concentration under all operational conditions, the requirements of the standard are met.

 

When selectively reducing the power being fed to the fan units, it is important to bear in mind any required pressure
differential between the area in question and adjoining areas. For example, a “gowning-up” area adjoining a cleanroom needs to be held at a lower pressure than the cleanroom itself so that staff moving from the gowning-up area into the cleanroom do not take large quantities of airborne particles with them.

Another opportunity to minimise a cleanroom’s carbon footprint without compromising its cleanliness is by reducing power consumption when it is not being used. This is not as simple as “switching off” the fans and lighting at night. A certain base level of airflow is required to prevent ingress of particles from the surrounding environment, any required pressure differentials with ancillary areas must be maintained, and a minimal level of lighting should be provided for safety purposes. However, if this “base airflow level” can be determined and provided together with a minimal lighting configuration when the cleanroom is at rest, further considerable CO₂ savings can be made.

 

To take advantage of these findings and assist with the transition to a reduced carbon footprint cleanroom environment, a sophisticated closed-loop cleanroom control system has been developed. This incorporates a real-time particle counter; pressure, temperature and humidity sensors; and lighting control electronics that provide all of the benefits outlined above. It also manages the pressure differential between a main and an ancillary room, and provides enhanced audit trail and management information statistics capabilities.

Recent advances in lighting technology also allow users to reduce their carbon footprint without affecting operational efficiency. For example, a 1200 mm 15-W LED tube will produce 1450 to 1600 lm, which is equivalent to a 36-W fluorescent tube. During one year of operation (8 hours per day, 5 days per week, 50 weeks per year) this represents a saving of 0.021 kg of CO₂ annually per tube. As an added advantage, because unlike most fluorescent tubes LED tubes contain no mercury, the issues concerning safe disposal of mercury-containing products are eliminated.

Cleaning agents. If the practice of flooding excessive amounts of filtered air into traditional cleanrooms is metaphorically speaking overkill, the current approach used to maintain the cleanliness of cleanroom surfaces is literally overkill. Unnecessarily large amounts of cleaning products are employed that are needlessly harmful to the environment. A far preferable and more environmentally friendly approach would be to systematically assess the cleanroom’s cleanliness, the likely contaminants and the potential impact of contamination. Then a cleaning regime can be designed in which the smallest possible amount of the least environmentally harmful (yet appropriate) product is used to attain the required result. To assist in this process, Table I shows the primary classes of cleaning agents that are available, their functional advantages and disadvantages and their ecological impact. This is, of course, an area where progress in environmental terms is constrained by the opinions of European regulatory bodies and the United States Food and Drug Administration, because innovative products and practices often require extensive time and resources to attain the necessary certification.

 

Single use garments versus limited-life and launderable versions. Another area where the environmental impact of cleanroom consumables could be improved is the current widespread use of single-use garments for cleanroom operators. Consideration should be given to the use of limited-life garments such as those constructed from Tyvek (DuPont, www.dupont.com), which can be re-used to some extent and thus reduce the amount of land-fill waste produced, or to launderable garments and their associated cleanroom laundry services. This latter option is, however, potentially less environmentally friendly than it appears, because it tends to involve extensive transportation and packaging of a daily change of garments. Obviously these alternatives would not be relevant to all cleanroom applications, but where they fit in with the user’s modus operandi they can deliver significant
environmental benefits.

In addition to the environmental advantages that can be achieved through reducing the airflow through cleanroom filter units, running costs can also be drastically reduced. A fan that consumes 470 W at full power to produce an airflow of 80 cm/s, burns 0.94 kWh during one year of operation (8 hours per day, 5 days per week, 50 weeks per year). If the power to the fan is reduced to 220 W, which causes it to produce an airflow of 50 cm/s, it will consume only 0.44 kWh per year. This represents a considerable saving, especially when multiple fan units are in use.

 

A less obvious, but equally impressive, advantage of reducing fan speed whenever possible is that, because the efficiency of a typical filter unit increases as the airflow decreases, the air being used to dilute the concentration of particles is itself cleaner and thus the dilution process is more effective. Furthermore, if only the minimum necessary throughput of air is being processed, the life of the relevant filters will be considerably extended, causing them to require less frequent replacement.

 

Once the outlay for the more energy-efficient lighting units has been recouped, savings of approximately 50% in day-to-day running costs can be expected.

 

In the system discussed here, a real-time particle counter is constantly monitoring the cleanliness of the cleanroom environment, pressure sensors are monitoring the state of the filters and a computer system is adjusting the speed of the fans and configuration of the lighting according to the inputs from these sensors and the production requirements. A mass of detailed management information can be collected, as shown in Figure 2. This allows managers to spot trends such as temperature- or humidity-related product variations, and to analyse exceptions such as sudden spikes in particle count resulting from, for example, a member of staff entering the room without gowning up properly.

 

Because of the clear environmental advantages that can accrue from transitioning to a cleanroom with the features described above, it should be possible to obtain financial assistance from organisations such as The Carbon Trust² to offset the initial outlay involved.

 

There is considerable scope for reducing the environmental impact of a typical cleanroom. Limiting fan speeds to the minimum necessary to ensure the required particle count is maintained can attain large energy savings. More efficient lighting can be employed. Production of landfill waste can be reduced by using a cleanroom garment laundry service. Using the smallest viable amount of the least-harmful product that fulfils the required objective can reduce the environmental impact of cleaning products. Measures such as these can also bring considerable collateral benefits such as reduced energy bills, closer adherence to standards and enhanced manageability of the cleanroom environment. It is truly a win–win proposition. 

is Managing Director at Connect 2 Cleanrooms Ltd, Unit 2 Kirkby Lonsdale Business Park Kirkby Lonsdale LA6 2HH, UK
tel. +44 15242 74170, e-mail: info@connect2cleanrooms.com, www.connect2cleanrooms.com