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Selecting the right microbiological air sampler

Supplier: Kenelec Scientific
04 May, 2010

According to ISO 14698-1 2003 Annex A.3.2, there are many factors to consider when choosing an Air Sampler.

The sampling rate duration of sample and type of sampling device can strongly influence the viability of the micro-organisms that are collected.

Because of the number and variety of microbial air sampling systems commercially available, the selection for a particular application should consider, as a minimum the following factors:

  • Type and size of viable particles to be sampled.
  • Sensitivity of the viable particles to the sampling procedure.
  • Expected concentration of viable particles.
  • Ability to detect high or low levels of bio contamination.
  • Appropriate culture media.
  • Time and duration of sampling.
  • Ambient conditions in the environment being sampled.
  • Disturbance of unidirectional airflow by sampling apparatus
  • Sampler Properties such as:
    1. Appropriate suction flow rate for low levels of viable airborne particles.
    2. Appropriate impact/airflow velocity.
    3. Collection accuracy and efficiency.
    4. Ease of handling and operation.
    5. Ease of cleaning and disinfection or sterilisation.
    6. Possible intrinsic addition of viable particles to the bio contamination to be measured.

The exhaust air from the sampling apparatus should not contaminate the environment being sampled or be exasperated by the sampling device.

This is a critical part to ISO 14698 but is somewhat overlooked. For example as the media becomes desiccated by the constant airflow passing over the media plate the media breaks up and media particles are carried out through the exhaust of the air sampler and blown around the cleanroom. It’s not what you want in your cleanroom. Effectively the Air Sampler is contaminating your cleanroom.

Microbiological Air Sampling of Cleanrooms is carried out to ensure that levels of airborne micro-organisms are within recognised international stan- dards.

There are two categories of air sampling:

  • Passive air sampling devices - such as Settle Plates; and
  • Active air sampling devices - such as Impact, Impingement and Filtration.

Air sampling methods include:

  • Inertial Impact,
  • Centrifugal,
  • Filtration and
  • Sedimentation.

Inertial Impact has become very popular over the last couple of years mainly due to the ease of use and the fact that the Petri dishes are easily placed and removed from the air sampler and put straight into incubation with minimum post sample contamination probability coupled with the fact that this method is very effective at capturing airborne micro organisms which tend to remain in the air longer than larger particles which are captured by settle plates.

Therefore it is vital to follow ISO-14698 the most important part is in select- ing the correct air sampler for your specific application. With so many different models on the market it is hard to see the woods from the trees. But if you follow ISO 14698 it becomes easier to identify a good quality air sampler

Badly designed air samplers contribute to this type of problem. It is up to the Micro Manager to validate these instruments. So its important to choose the correct instrument in the first place. Another factor is Collection Accuracy and Efficiency of the air sampler.

This equates to the physical and biological properties of the air sampler. The design of the air sampler is key to collection accuracy and efficiency. The impaction velocity is critical in maintaining good biological efficiency and the head design of the air sampler is also critical in maintaining good physical efficiency.