Air processing and controlling atmospheric turbulence

The environments in which food products are processed and packaged are becoming ever cleaner. The traditional techniques based on clean rooms and laminar flow do not always provide adequate protection against microbial contamination by air particles. This is particularly true at the end of the production chain when procedures are such that the product necessarily comes into contact with free air. It is vital in such cases to achieve absolute cleanliness around the product in spite of the presence in the workshop of sources of contamination (people, machines or other organic products).

In a bid to address the shortcomings of existing methods, irstea undertook research on close protection systems. We have developed an innovative technique: Progressive Flow. Close protection not only increases food safety but also reduces costs and investment needs and the operational requirements of clean rooms.
All of these techniques are sensitive to disturbances in the protective air flows caused by the breaches that occur in industrial workshops during the inevitable activities prior to final assembly (inspections, packing, decoration, packaging).
We conduct research on the breaches at the interface between the protected area and the polluted ambient air. These studies are needed to improve existing protection apparatus and to develop more generic close protection techniques.
Alongside our air processing research, we aim to continue to influence air quality by undertaking vigorous actions to gauge the various aspects of air quality in accordance with our holistic vision of creating effective clean rooms in the food industry. The Air Quality Measurement team has a continuous measuring chain for assessing all of the variables that determine air quality in the food sector, including analysis of contaminated particle sizes. Our Metrology laboratory, in which the staff have appropriate and up-to-date education, specialises in checking the physical quality of air and providing services to industry to increase the efficiency of clean rooms in the food sector.


Main results

Progressive flow for localised protection of food workshops

Progressive Flow is a close protection technique to be used in sensitive areas located under a work station or conveyor belt. What makes it original is that it confers open protection in ambient air, even if there is human or robotic activity that entails penetration with devices such as dosing heads or arms.

Fruit of a collaboration between researchers and industry geared towards innovation

Progressive flow was designed by Irstea on the back of digital simulations of airflow. The validating experiment and development for industrial use were carried out as part of the Ultra-clean Factory programme that was launched in 1990 by the UNIR (Ultra-clean, Nutrition, Industry and Research) comprising nine food companies. This programme was managed by the industrial producers under the supervision of the ministries responsible for research, agriculture and industry, who supplied 40% of the funding.

The performances of Progressive Flow were validated on an actual size prototype, firstly in a laboratory and then in a real-life situation in an industrial plant. It was designed to meet hygiene standards on the basis of technical specifications drawn up by Irstea.
Irstea and UNIR jointly hold the patent for this. They have introduced a licensing process for small- and medium-sized industries that specialise in air processing equipment.

Controlling the clean air/polluted air interface

Localised protection techniques entail blowing ultra-clean air into polluted environments and confining it there. The physical mechanisms deployed at the interface of clean air and polluted air are often highly complex, especially when the clean air flows are hampered by fixed or moving obstacles during work on products. It is vital to understand the interactions that take place at this point in order to enhance existing techniques and develop processes that are suitable for an array of industrial situations. 
In the case of progressive flow, a model was built with a round tool hold insert dipped in a mixed layer with active turbulence to depict the obstruction of airflow during work on a food product on an ultra-clean production line. This experimental study was conducted in tandem with the CEAT/LEA (aerodynamics study centre) of the University of Poitiers. The highly three-dimensional nature of the airflow made it necessary to use a probe with four hot wires, enabling simultaneous and instantaneous capture of the three components of the air speed.
Our findings revealed a significant airflow in the obstacle's base area that is detrimental to food protection. A sound understanding of the dynamics deployed at this point of the airflow enabled us to formulate a strategy to deflect contaminants.


Measuring air quality

The food industry requires keen awareness of quality and safety and aims to achieve total eradication of contamination. Cemagref offers a diagnostic method based on the continuous measurement of all the constituent variables of air quality.
Levels of intervention

  • measuring particle contamination
  • determining class of cleanliness
  • kinetics of particle decontamination
  • measuring airflow and circulation rate
  • gauging air renewal rate with tracer
  • air speed at work station
  • measuring pressure cascades
  • measuring sound and light level
  • measuring temperature and hygrometry
  • air circuits characterisation

All of the measurements are performed at set intervals or continuously.

Checking and validating the installed system

Air quality diagnosis is built into the brief of a research team working on ultra-clean blowing apparatus for the close protection of sensitive areas. Upon requests from industry, the team's expertise can be deployed to investigate specific solutions for identified critical points.


Scientific and technical partners

Institutional partners

  • Ministry for Agriculture, Food, Fisheries, Rural Life and Land Use
  • Ministry for Higher Education and Research
  • The Brittany Regional Authority
  • The Poitou-Charentes Regional Authority
  • The Lower Normandy Regional Authority

Industrial partners

The Air Processing and Bio-contamination team is involved in applied research programmes in collaboration with manufacturers and fitters of equipment for air processing for the food industries and other sectors.

We also provide consultancy to companies in the food sector.

Composition of the team

Team leader Dominique Heitz 

Johan Carlier
Christophe Collewet
Lionel Fiabane

Engineer - *Assistant engineer Philippe Loisel
Laurence Wallian
Philippe Georgeault*   
Post-doctoral Yacine Ben Ali
Romain Schuster
Yin Yang