Thank you Charles.
I will try to get hold of the Tesco Manual.
This was an ALDI audit.
A little more info from FDA -
Air and air flow
We recommend that you design the air flow in your plant to maintain positive air pressure on the
RTE side of the operation relative to the “raw” side (i.e., maintain higher air pressures in RTE
areas and lower air pressures in areas where unprocessed (“raw”) foods are handled). We
recommend that you consider the room temperature and the impact of airflow on controlling
condensation in the plant. We also recommend that you consult individuals with appropriate
engineering skills to determine how to achieve proper air balance and the desired air exchange
rate, including determining the number, size, and location of intake and exhaust fans.
There have been isolated reports of contamination associated with air (e.g., air from
compressed air lines has been implicated in contamination traced to a niche (i.e., growth in a
filter) near the point of use (Ref. 44). We recommend that you consider filtering the air in rooms
where RTE foods are processed or exposed to reduce the potential for contamination of RTE
foods with microorganisms (including L. monocytogenes). If you filter the air, we recommend
that the final filter have an efficiency of at least 90-95 percent at 1 micron as rated in American
Society of Heating Refrigerating and Air-Conditioning Engineers (ASHRAE) standard 52.2-
Depending on your product, your process and the design and construction of your plant,
it may be appropriate to use High Efficiency Particulate Air (HEPA) filters that have an efficiency
of 99.97-99.99 percent at 0.3 micron for removing bacteria, yeasts and molds.