Application Note

Impact of the new EN 17141 on the ISO

14698 Validation of MAS-100® Air Samplers
General Requirements and Validation

The scope of the new norm is to establish the The basis for an efficient microbial air sampler is a good
requirements, recommendations and methodology physical and biological efficacy:
for microbiological contamination control in clean
"The physical collection efficiency is the cut-off size
controlled environments. The document is limited to
(d50 value) which defines the aerodynamic equivalent
viable microbial contamination and refers to ISO 14644
particle diameter size at which the sampler collects 50
about non-viable contamination. ISO 14698 is valid
% of the particles in the air [12] [13]. The average
throughout the rest of the world while EN 17141 2020
equivalent diameters of microbe-carrying particles
will replace it in the European Union.
(MCPs) that form the cfu are generally larger than 1
This application note will evaluate if the new EN µm and a d50 value smaller than 2 µm is considered
17141 norm will affect the validation requirements of appropriate. The d50 value can be calculated for
volumetric air samplers described in ISO 14698. impaction samplers with multiple holes or those using
rectangular slits. For active air samplers based on
Comparison of EN 17141 and ISO 14698 impingement and or cyclonic operational principles,
no d50 value can be calculated. For all active
requirements on microbial air samplers
microbiological air samplers, the effects of impact
stress and the effect of the media dehydration during
ISO 14698 requirements for microbial air samplers are
the sampling period are further considerations.
more detailed, but generally match the requirements of
EN 17141. The physical collection efficiency is influenced by
both inlet or extraction efficiency and by separation
The requirements for validation are newly defined in the
efficiency. Inlet or extraction efficiency is a function
EN 17141. The supplier of the sampler shall demonstrate
of the inlet design of the sampler and its ability to
the collection efficiency of the sampler, the sampling
collect particles from the air in a representative way
techniques shall be validated, and the volumetric air flow
and transport the particles to the impaction nozzle
of the sampler shall be periodically calibrated.
or the filter. Separation efficiency is the ability of the
sampling device to separate and collect particles of
different sizes from the air stream by impaction onto
the collection medium or into the filter medium. The
physical collection efficiency is based on the physical
characteristics of the sampling device such as airflow,
orifice shape, orifice size and the number of orifices."

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The following table will compare the requirements for sampling devices, especially volumetric microbial air
samplers as indicated in EN 17141 and ISO 14698-1.

Table 1. Comparison of requirements for sampling devices and microbial air samplers in
EN 17141 and ISO 14698:
Requirements EN 17141 Corresponding Requirements out of ISO 14698
Accessibility into the clean controlled environment for the sampling device • Ease of cleaning and disinfection or sterilization
• Ease of handling (weight, size) and operation (ease of
use, auxiliary equipment, dependence on vacuum pumps,
water electricity, etc.)
Effect of the sampling device on the process or environment to be monitored • Disturbance of unidirectional air flow by sampling
apparatus
• The exhaust air from the sampling apparatus should not
contaminate the environment being sampled or be re-
aspirated by the device
• Possible intrinsic addition of viable particles to the
biocontamination to be measured
Efficiency and precision of the sampling method • Collection accuracy and efficacy
.. a d50 value smaller than 2 µm is considered appropriate … / …For all active • Appropriate suction flow rate for low levels of viable
microbiological air samplers, the effects of impact stress and the effect of the airborne particles
media dehydration during the sampling period are further considerations • Appropriate impact/airflow velocity
• Sensitivity of the viable particle to the sampling procedure

Requirements and Methods for the

Validation of Microbial Air Samplers
The method for a complex validation of microbial air As an alternative, a simpler method is added to the
samplers is described in both norms with no significant complex method in order to allow on-site validation. This
differences. According to EN 17141 this complex method is a side-by-side comparison against an already
method should be preferably performed by an external qualified air sampler that has been validated to the
competent body and the supplier of the air sampler more complex biological and physical efficiency method.
shall demonstrate the collection efficiency of the The simplified test should be performed in minimum at
microbial air sampler. A re-validation of a qualified two different locations with a contamination level of in
instrument is not required. minimum 80 cfu/m3. he chosen sampling volume should
result in a count of 80 to 150 cfu per plate. A previously
The method for validation of collection efficiency is qualified instrument or membrane filtration method may
separated into the validation of the physical efficiency be used as a reference.
and the biological efficiency. The physical efficiency
demonstrates the ability of the air sampler to collect If using a qualified instrument, which is validated by
various particle sizes down small particles sizes, such the supplier according to the described method in
as 1 µm. The d50 value indicates the particles size Annex E of 17141, an on-site simplified validation as
at which 50% of the airborne particles are impacted well as a re-qualification is not required.
onto the agar surface by the microbial air sampler. The
biological efficiency is the ability of the air sampler to
safely capture organisms from the air.
A new requirement according to EN 17141 is a defined
d50 value of smaller than 2 µm, which was not
specified before in the ISO 14698-1.

2
Validation Results for MAS-100® Microbial Air Samplers
Every variance of air flow, such as flow rates or configuration of the sampling head (e.g. numbers and size of holes of
the sieve plate) might influence the physical and biological efficiency of microbial air samplers. Therefore, we validate
various instruments of the MAS-100® air sampler family at a competent external body (PHE Biosafety group in Porton
Down), England individually. The qualified instruments are indicated in figure 1.

2.
1.

4.
3.

Figure 1. Instruments validated according ISO 14698 and consequently to EN 17141 by an external competent body

1.1. MAS-100 NT® (instrument configuration identical to 1.3. MAS-100 Iso NT®
MAS-100 NT® with filter and MAS-100 NT Ex® with or 1.4. MAS-100 Iso MH® (2 separate validations for either 1 m or 9
without filter) m tube length between sampling head and control unit)
1.2. MAS-100 VF®

The validation of the physical efficiency takes place in better than the calculated values. The calculated d50
test room of 20 m3 with turbulent air. The test sampler of the tested microbial air samplers is 1.1 µm at a flow
and reference membrane filtration device are positioned rate of 100 liter/min and using a sieve plate with 300 x
in the same distance and height from the spinning 0.6 mm holes.
top aerosol generator. Washed spores of Bacillus
The biological efficiency is validated against a Casella
atrophaeus NCTC 10073 are mixed with different
Slit Sampler and the results are indicated in figure 3.
concentrations of potassium iodide in order to achieve
The biological efficiency is calculated by the recovery
the various particles sizes. The spores are distributed
of the ratio of cfu of a mixture of Bacillus atrophaeus
homogeneously using spinning top aerosol generator
NCTC 10073 spores and Staphylococcus epidermidis
to the sampling devices. As culture medium TSA w.
NCTC 11047.
LTHTh - ICRplus (reference number 1466830020) plates
are used. After sampling, the filter is transferred on Biological efficiency = Ratio of SE/BA sampled by test
to culture medium plates and all plates are incubated. device/Ratio of SE/BA sampled by Casella Slit sampler x100
Afterwards the CFU are counted and the recovery rate
for each particles size is calculated. The biological efficiciency of the MAS-100® air samplers is
indicated in figure 3. For all tested MAS-100® microbial air
The test results of the validation of physical efficiency samplers, the biological efficiency is above 70%.
of the instruments show a d50 value of less than 1 µm
for all test samplers (see figure 2). The test results The full test reports can be reviewed during an audit.
are comparable for all tested instruments and are

3
Figure 2. Test results of physical efficiency for various MAS-100® Figure 3. Test results of biological efficiency of various MAS-100®
microbial air samplers microbial air samplers

Conclusion References
• EN 17141 (2020): Cleanrooms and associated controlled
The requirements for volumetric microbial air environments - Biocontamination control
samplers do not differ significantly between the • ISO 14698-1 (2003): Cleanrooms and associated controlled
environments - Biocontamination control - Part 1: General principles
EN 17141 and ISO 14698-1. They should provide and methods
accurate and reliable results. • Physical and Biological Efficiency Testing of MAS-100 VF® - Techniques
described in ISO 14698-1: Report No. 14/013 A (2015) - (PHE Biosafety
The MAS-100 NT, MAS-100 VF, MAS-100 Iso NT ®
group in Porton Down)
and the MAS-100 Iso MH® have been validated • Physical and Biological Efficiency Testing of MAS-100 Iso MH® - 1m -
according to the requirements of ISO 14698-1 Techniques described in ISO 14698-1: Report No. 14/013 B (2015)
- (PHE Biosafety group in Porton Down)
and consequently to EN 17141 by an external
• Physical and Biological Efficiency Testing of MAS-100 Iso MH® - 9m -
competent body. Techniques described in ISO 14698-1: Report No. 14/013 C (2015)
- (PHE Biosafety group in Porton Down)
The physical efficiency is comparable for all tested
• Physical and Biological Efficiency Testing of MAS-100 Iso NT® -
instruments and provide a d50 value of less than Techniques described in ISO 14698-1: Report No. 14/013 D (2015)
1 µm. The biological efficiency is above 70% - (PHE Biosafety group in Porton Down)
compared to a Casella Slit Sampler. • Physical and Biological Efficiency Testing of MAS-100 NT® - Techniques
described in ISO 14698-1: Report No. 14/013 E (2015) - (PHE Biosafety
According to the validation results a re- group in Porton Down)
qualification of these instruments is not required.

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