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Changes in the standard and updates to hex operating methods


I – Particle classification: Standard ISO 14644-1 and 2 2015 version


After 10 years of discussion and no fewer than two DIS draughts, the two new parts 1 and 2 of ISO 14644 have just been published on the International Organization for Standardization (ISO) website. The revision process, which began in 2005, has resulted in significant technical changes with a direct impact on the work performed by HeX.

ISO 14644-1:2015 thus becomes the sole reference document for the classification of the air cleanliness by particle concentration of clean rooms and associated controlled environments, specifying classes of air cleanliness by particle concentration and also the standardized test method.

As an accredited test laboratory, HeX undertakes to comply with and apply the versions of available international standards in force. Following above the changes in the standard, HeX’s operating methods have, therefore, been updated. As these are scheduled to be implemented in full during May 2016, the next work we undertake will be carried out in accordance with the new version and our reports will refer to it.

What changes have in fact been made?

The main changes are as follows:

1 – Elimination of a number of targets and new procedure for macro particles.

Table 1 in ISO 14644-1:2015 describes the maximum allowable concentrations for each size of particle. The values have not been changed, but a few have been deleted from the table, because of the sampling limits for these very low concentrations make classification inappropriate.

*For macro particles ≥5,0µm the annex C of the standard provides a procedure according the descriptor M. Therefore users that need to comply with GMP regulations or users who want to keep this particle size, can keep this target.

Table 1 – ISO classes of air cleanliness by particle concentration


 2 -Statistical treatment and number of sampling points

One of the most significant changes concerns the elimination of use of a complex statistical approach.

A new approach is defined based on an adaptation of the hypergeometric sampling model technique. It allows each sampling point to be examined individually in order to check, with a confidence level of at least 95%, that at least 90% of the room surface is in compliance with the class targeted. During the revision process, it was clearly recognized that the 95% upper confidence limit (UCL 95%) was not appropriate. The minimum number of sampling points required was therefore changed from that in ISO 14644-1:1999. Table A.1 of part 1 of ISO 14644 defines the number of points NL based on the clean room surface area. Generally speaking, the number of points has been increased by 32% on average.

 3 – Method of distribution of the counting points or sampling locations.

In the ISO 14644-1:1999 version, there is no requirement with respect to the actual distribution of the particle counts across the entire clean room. Only a uniform distribution of the sampling points in the clean room air was addressed. With the revision of the document, the location of the points is described with the clean room surface being divided into sections of equal surface area, the number of sections being defined by the number of points obtained from table A.1. A representative sampling point is identified in each of these sections.

4 – Method for demonstrating conformity

As the 95% upper confidence limit (UCL 95%) no longer applies, only the average particle concentrations at each sampling point expressed as the number of particles/m3 are used to demonstrate conformity.

If the average measured is lower than the limit, the classification is considered as conforming.

If the average measured is higher than the limit, the classification is considered as non-conforming.


II – Assessment of the microbiological quality of the air and surfaces


In the interest of always offering a professional, relevant, high-quality service, HeX has decided to update its operating methods associated with microbiological inspections.

In the context of ISO 17020 accreditation, the sampling programmes conducted by HeX in order to demonstrate the conformity of a clean room (number of points and nutritive media used) were conducted as follows:

  • A number of sampling points defined based on the surface area to be inspected (Table No. 01: Number of points based on surface area)
  • Types of nutritive media chosen on the basis of the environment in question (Table No. 02: Choice of nutritive media)

Table No. 01: Number of points based on surface area


Table No. 02: Choice of nutritive media


A risk analysis was conducted taking into account the relevant elements such as the microbiological analysis of the bacterial and fungal organisms, the numbering limits, good practice in the incubation of the nutritive media and the distribution and random occurrence of the organisms in the air and on the surfaces, etc.

Thus, HeX developed operating methods for microbiological inspections as follows:

Table No. 01b: Number of points based on surface area


Table No. 02b: Choice of nutritive media


*The new standardised choice of nutritive for HeX is a total flora media except prior agreement between client and supplier stipulates otherwise.

The zones in the microbiological sampling programmes that are affected by these changes in operating methods are, therefore, those where:

  • the surface area is greater than 9m².
  • the environment in question is a ‘hospital’ type environment and the applicable criteria are defined by French standard NFS 90-351, and CSS/HGR notice No. 8573 and all GMP/BPF environments.

HeX will be pleased to provide any additional information and would like to thank you for your interest in its work.


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