Food factory hygienic zoning: raw, ready-to-eat and support areas

By ZY Cleanroom · Updated 2026-11-01 · Sources at the end of the page

FDA's four sampling zones

FDA gives this as an example of how to characterise a plant (Table 4 of the draft). It is a monitoring tool, and it also helps to plan the layout.

Layout advice in the draft

For new builds and renovations, FDA recommends separating RTE areas from raw areas. It also recommends separating them from equipment washing, microbiology labs, maintenance, waste, offices, lockers and toilets.

The draft says to place the microbiology lab as far from processing as practical, preferably in another building. It says not to fit windows that open in RTE areas. It also says not to use porous or absorbent materials, such as wood or foam, in RTE areas and wet areas.

Where practical, give RTE staff their own locker, break and cafeteria areas.

Air in a zoned plant

FDA recommends positive air pressure on the RTE side relative to the raw side. Its Appendix 3 shows one plant with a partition between raw and RTE areas and one that relies on positive pressure without a partition.

Keep air intakes away from exhausts and waste areas. If you filter the air, FDA suggests a final filter of at least 90 to 95 percent at 1 micron under ASHRAE 52.2-2012. Depending on product and process, HEPA filters at 99.97 to 99.99 percent at 0.3 micron may suit.

The draft is nonbinding and not final. It also points to 21 CFR 117.20(b), which asks for structures suited in size, construction and design to sanitary operation.

Drains, water and condensate

FDA recommends not installing trench drains in RTE areas and, where practical, replacing existing ones with enclosed plumbing to a floor drain. Floors should slope so water does not pool. Drains should not flow from raw areas to RTE areas, and restroom drains should not join RTE drains.

Sewer lines should not run above RTE areas. If they must, shield them. Part 117 requires that drip or condensate from fixtures, ducts and pipes does not contaminate food (21 CFR 117.20(b)(4)). Dehumidifiers and adequate ventilation can help.

People, carts and pallets

FDA recommends controlling the traffic of staff, products, packaging and equipment between raw and RTE areas. Give each side its own carts, forklifts, mobile racks and pallets. If that is not practical, clean and sanitise wheels before they enter the RTE area.

Colour-code smocks by area and task. Where lockers must be shared, FDA suggests an entry room for RTE smocks and footwear, a captive shoe policy, and a chemical barrier such as a footbath or foamer.

Both plastic and wooden pallets can carry Listeria. FDA says plastic is better suited to wet areas.

Worked example (arithmetic)

FDA's example plan, for a food that supports Listeria growth, samples zone 2 weekly, zone 3 every two weeks and zone 4 monthly, with every site tested at least quarterly. As an illustration, say a plant samples 10 sites in each of zones 2, 3 and 4. In four weeks that is 10 × 4, plus 10 × 2, plus 10 × 1, which is 70 samples.

More zone 2 sites means more work in the lab, so plan the number of sites at the layout stage.

If you have a room list for a food plant, send it to ZY Cleanroom and we will review the panel, door and ceiling scope with you.

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Sources

• FDA, Draft Guidance for Industry: Control of Listeria monocytogenes in Ready-To-Eat Foods (January 2017, draft, nonbinding; checked 1 November 2026)
• FDA, guidance listing for the same document, marked draft and not for implementation (checked 1 November 2026)