Recent revisions and new progress on cleanroom standards

As technology evolves and cleanroom techniques advance, the BS/EN/ISO 14644 family of standards that affect cleanroom practices require updating or, in some instances, completely new standards are introduced.

To keep the cleanroom sector up to date on these changes, the British Standard Institution (BSI) recently held a one-day seminar in London, where industry experts from the relevant working groups (WGs) discussed the recent revisions, as well as new and proposed standards.

Gordon Farquharson, Critical Systems, Chair of LBI/30, CEN TC243, and Convenor of ISO TC209 WG1, gave an overview of the activities of the BSI LBI/30 committee, which plays an active role in developing national and international standards for cleanrooms. He said that two expert groups hosted within LBI/30 are:

• the Microbiological cleanliness group, chaired by Tony Harrison (Beckman Coulter), which is working on the creation of a European (CEN) standard for microbiological cleanliness, and
• the Energy Management of Cleanrooms group convened by Dick Gibbons, which recently introduced the BS 8568:2013 energy standard.

LBI/30 also has a committee, chaired by Farquharson, that periodically reviews the CEN TC243 standards, and in his second presentation Farquharson looked in detail at the revisions of BS EN ISO 14644 parts 1 and 2 that were approved in December 2015.¹

These revisions are some of the most important since the standards were introduced, as they affect the way that cleanrooms are classified as well as many other aspects of operation and monitoring.

In the afternoon, Tim Triggs, DOP Solutions and expert member of LBI/30, gave a more detailed workshop on the revisions to ISO 14644-1 & 2: 2015 with a particular focus on particle counting and cleanroom classification, highlighting how to attempt some of the calculations involved.

TOC209 origins and projects

Another speaker, John Neiger, Clean Air and Containment Review and member of LBI/30, provided an overview of the activities of Cleanrooms and Associated Controlled Environments Technical Committee ISO/TC209.

This group was formed in 1993, when it was decided that the many national standards should be amalgamated into one set of international standards.

TOC209 is thus responsible for the ISO 14644 series of cleanroom standards and also ISO 14698 series (see Table 1). The 23 key participating member countries send representatives to the different working groups and some observing-members also attend. The process of getting a standard accepted and published can take years – it took six to introduce the first standard in 1999.

Table 1: Status of Standards in ISO 14644/14698 series

Neiger said there are currently 11 ISO 14644 standards published which can be divided into, ‘General cleanliness attributes’ and ‘Other’ standards.

He explained that a further six standards are under development and one is under consideration.

The 13 working groups of TC209 meet once a year, generally coinciding with the biennial ICCCS or, in the intermediate years, with a suitable national meeting. The working groups often meet more frequently as necessary.

Neiger explained how the standards progress from a concept to a new work item proposal (NWIP), a working draft (WD), a committee draft (CD) and a draft international standard (DIS). This is the version that is put out for vote and comments and is the last stage at which technical changes can be made. If the DIS is approved the final draft (FDIS) is prepared for editorial changes only.

Developments in ISO cleanroom-related standards

In total there are 16 ISO cleanroom-related standards but not all apply to ‘all’ cleanrooms. Neiger went through the different standards to help delegates pick out those relevant to their business and to explain where they were in terms of revisions and being published. He then discussed some of the more recent standards:

For example, Part 13: Cleaning of surfaces to achieve defined levels of cleanliness in terms of particle and chemical classifications, which is at the DIS stage.

Neiger said there were some reservations about this standard from the UK sector, as it applies mainly to components rather than to cleanroom surfaces, so it is more of a process standard than a cleanroom one.

Part 15: Assessment of suitability of equipment and materials for cleanrooms by airborne chemical concentration is at the DIS stage and awaiting formal approval.

The DIS is currently being prepared for Part 16: Code of practice for improving energy efficiency in cleanrooms and clean air devices and it is thought that the relevant airflow calculations involved will be moved to ISO 14644-4.

Part 17: Specification of requirements for particle deposition monitoring has been proposed as a new project (NWIP) and is being voted on.

Neiger said that this standard could become quite interesting because, he argued, ‘what is actually important in a cleanroom isn’t so much the contamination in the air as the contamination that is deposited onto the product being produced’.

He then discussed the ISO 14698 Biocontamination control standard, which includes: Part 1: General principles and methods and Part 2: Evaluation and interpretation of biocontamination data. Neiger said that a proposed revision of this standard was rejected by ISO but that CEN has picked up the work and may produce a standard in Europe, which may be adopted later.

Table 2: ISO/TC209 Working Groups

New energy standards

Process Designer, BSI and ISO 14644 WG Convenor Dick Gibbons looked at the relatively recent energy standard BS8568:2013, explaining the reasons for its introduction and its content, which is largely to do with airflow and air change rates.

It was the very first cleanrooms in the 1950–60s that introduced the concept of using horizontal laminar airflow (now termed unidirectional airflow or UDAF) whereas today turbulent non-unidirectional airflow (non-UDAF) is used with localised UDAF in the critical process areas as necessary.

The traditional practice was to have frequent air changes to ensure there was no risk of contamination (covered in ISO14644-4).

However, the approach is very energy intensive. According to Gibbons, typical ISO 6 room parameters for today’s microelectronics cleanrooms would be, for example:

• less than 35,000 particles of above 0.5 microns pre cubic metre of air per min.
• above 15–25 pascals of room pressure above ambient
• less than 10,000ng of organic and ionic residue per cubic metre (for semicoms)

While the energy related parameters would be:

• air speed 0.3–0.5m/sec
• air change rate 40–70/hr
• temperature +/-2°C
• lighting 500–700 lux

But since the 1960s, energy costs have steadily risen; recent wars have caused oil shortages, global warming and carbon footprints have become an issue, budgets have tightened and austerity measures have been introduced.

As a result, companies are starting to challenge ISO 14644-4, not only in Europe but also in the US and even China, which Gibbons said is now looking to slow its energy consumption.

The energy issue led to an ISO 14644 BSI Expert Sub-committee being formed, comprised of Gordon Farquharson, John Neiger, Nigel Lenegan (carbon management), Peter Dyment (filters), Stephen Wake (design), Tim Triggs (pharma) and Gibbons himself. They put together a Code of Practice that had separate sections for existing- and new-builds and which challenged the ‘over-engineered’ ISO 14644-4 air flow requirements. The objective was to reduce total power use.

The resulting BS8568 is set out in the form of a check list and uses formulae for source strength and flow rates. To ensure the success of such projects, it also gives guidance on a project team structure as well as on heating and cooling, filter selection, lighting and maintenance.

It introduces the concept of ‘turn down’ (turning down power at weekends or periods when cleanrooms are not in use) and of ‘cautionary power off’ procedures’ – which many companies already employ, said Gibbons.

A key item of the standard is ‘Basic energy reduction methods’ which come with tables and explanations.

The new concept of matching supply air volume flow rate to the contamination source strength replaces air change rates or room turnover/hr. Formulae based on Bill Whyte’s formula for dispersion rate² and estimated sedimentation velocities are employed, but the formulae used have been rationalised.

Another section covers fan efficiency, depending on what sort of fan is being used. It introduces the concept of Specific Fan Power (i.e. electric power to air delivery percentage) to help decide what sort of fan power is actually needed to deliver the air flow required. It also gives guidance on efficient filter selection.

Another key item is cooling and humidity control. For example, in applications where electrostatic charge is not a product issue, it suggests allowing relative humidity to float in 30–70% mode.

The standard also discusses the high energy costs of latent cooling for humidity control (due to the required low water temperatures).

It looks at sensible cooling parameters for room heat load with management at twice the latent water temperature, and advocates separation of the two through separate distribution and control loops.

It also talks about the principles and the low energy values of DX chillers with fine controlled screw compressors, which are now available for use.

What can and has been achieved with the practical energy solutions given in the standard is a 20–30% reduction in energy use, said Gibbons, and he outlined some of the ‘quick win’ policy changes:

• minimise ceiling, door and floor leaks
• optimise air speed by sector management
• minimise site lighting at night
• allow partial fan shut down outside work shifts
• reduce fresh air make up volumes
• widen temperature and humidity control range

Capital-intensive projects that should be considered when starting new build include:

• introduce variable speed fan motors
• fan filter use for background control
• reduce air volume by correct process and room design
• redesign cooling supplies
• flow cabinets for small products

Moving towards ISO 14644-16

Gibbons is also convening the new WG13 on energy that is drafting ISO 14644-16, while the UK is challenging parts of 14644-4 Cleanroom design and helping the new WG4 (chaired by the Netherlands) with formating the energy section.

It is introducing concepts such as: Adaptive control, Airflow Formula, Benchmarking and Labelling, Safety Factors, Ventilation Efficiency and Quality Management.

It was also felt necessary to include a Quality Management section to ensure companies are able to satisfy the regulators about quality and safety. The working group hopes to get a CD out for ISO 14644-16 this Summer.

In terms of airflow it adopts the Russian’s ‘progressive approach’ for non-unidirectional airflow calculations. This involves a gradual turning down and fine tuning of systems, with safety factors related to ventilation efficiency as used in the US.

In addition, rather than specifying one equation it gives various examples in the standard. The Annex shows worked examples from classical dilution equations using a range of different personnel and machine contamination rates from research sources.

The standard is about to be released for comments but there are key disagreements still to be ironed out. For example, the benchmarking and labelling, which is considered as a management tool for comparing group or sites is disliked by Russia.

The adaptive control feedback system linked to particle counters to control air speed is not yet accepted by US pharmaceutical regulators. There is also dispute over garment release rates from differing sources. The risk management proposals are also disliked by Russia.

Gibbons emphasised the importance of cleanroom users making their views heard on these issues, as this standard is eventually likely to be enacted. Any comments are needed by the end of this year.

References

1. G. Farquharson, 2016. Major revisions of ISO 14644 parts 1 and 2 finally published,Clean Air and Containment Review,25(1) pp26–27

2. W. Whyte, K Agricola & M Derks, 2016. Airborne particle deposition in cleanrooms: Relationship between deposition rate and airborne concentration,Clean Air and Containment Review25(1) pp4–10