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HYGIENIC DESIGN · BUILDINGS · DRAINAGE
Key facts
- Channel profile U shaped with a rounded bottom, commonly cited at 150 mm wide
- Cover flat, apertures of about 20 mm, liftable by one person without a special tool
- Basket a sediment basket with a named owner and a recorded frequency
- Rated flow tested with a 20 mm water column above the drainage edge under EN 1253 conditions
- When to audit at the end of the wash, while the floor is still wet
- Course Module 5 of Intermediate Hygienic Design, nine hours
Audit your floors and drains properly
Module 5 of Intermediate Hygienic Design covers floors and drainage, the building envelope, air, pressure and condensation, utilities and building work in a running plant, and ends with the hygienic design risk assessment workshop. Nine hours, online, self paced.
The profile is the whole argument
Put two drains side by side in section and the decision makes itself. A U shaped channel with a rounded bottom sheds what the water carries, and a cleaning tool can reach every part of it. A square channel with a flat bottom holds whatever the water leaves behind, every night, for the life of the building.
Specify: a rounded bottom channel, commonly cited at 150 mm wide for a production room; the floor around it laid to adequate falls towards it so that nothing ponds; a flat cover with apertures of around 20 mm that one person can lift without going to find a tool; and a sediment basket with a name and a frequency against it. Then specify the material and the joint detail where the channel meets the floor, because that joint is where most drains actually fail.
The capacity question almost nobody asks
Rated flow in litres per second is a tested figure. It is taken with a 20 mm water column above the drainage edge, under the conditions the European standard sets, and not under the conditions in your plant during a wash down.
So ask two questions of the supplier and of your own team. What flow is this drain rated for, and what does the line actually discharge during cleaning? Reported water use in dairy runs from under one litre to twelve litres per kilogram of product, which is a very wide band, and a plant at the top of it will overwhelm drainage sized from a catalogue.
Standing water at the end of the wash means the drain lost that argument. It is a design finding, not a mopping instruction.
How to audit a room in one shift
Go at the end of the wash. Take a phone, a torch and somebody from engineering.
- Photograph every puddle. Standing water an hour after cleaning is a fall problem.
- Look at the joint between floor and wall, and at every piece of coving broken at a door frame where the pallet trucks hit it.
- Lift every cover you can and look at the bottom profile and the basket.
- Follow each drain line and find out where it crosses a zone boundary. Most sites have never drawn this.
- Look up as well. In a chilled high care room a great deal of the water on the floor arrived from above, as condensation.
The four findings almost every plant has
A drain running from a lower zone into a high zone. That is a vector, and it belongs on a drawing in front of management rather than in a list.
Cracked floor to wall junctions and broken coving at door frames. Cheap to fix while small, expensive once water is under the floor.
Standing water near an open product line. A fall fault, and the closer it sits to open product the higher it scores.
Hose points that let the team push soil across a zone boundary. A high pressure hose played on a grating aerosolises whatever is in that drain and puts it in the air of the room.
Turning it into money
Score every finding on severity, likelihood and exposure, one to three on each scale, and band the result. Anything in the top band gets an interim control the same day, not a plan. Then take the drain vectors to management as a drawing, because drainage is capital work, and capital work needs a drawing and a number rather than a complaint.
Frequently asked questions
What is the best drain profile for a food factory?
A U shaped channel with a rounded bottom, so that it sheds solids and a cleaning tool can reach every part of it, commonly cited at 150 mm wide for a production room. A square channel with a flat bottom holds residue and is the usual finding on older sites.
How much fall should a food factory floor have?
Enough that nothing ponds. Supplier and scheme guidance asks for adequate falls to drainage points rather than a single universal figure, and the honest test is what the floor looks like an hour after the wash. Standing water means the fall is wrong, whatever the drawing says.
What does rated flow mean on a drain specification?
It is a tested figure in litres per second, measured with a 20 mm water column above the drainage edge under EN 1253 conditions. It is a comparison figure between products, not a promise about your plant, so compare it against what your line actually discharges during cleaning.
When is the right time to inspect drains?
At the end of the wash, while the floor is still wet. Mid morning everything has dried and the faults are invisible. Walking it during cleaning also shows you how the team actually uses the hoses, which is often the finding.
Should drains run between zones?
A drain running from a lower hygiene zone into a high hygiene zone is a vector and should be designed out. Where it already exists, map it, control it, and put it on the capital plan. Start by drawing the drainage lines over your zoning plan, which most sites have never done.
Audit your floors and drains properly
Module 5 of Intermediate Hygienic Design covers floors and drainage, the building envelope, air, pressure and condensation, utilities and building work in a running plant, and ends with the hygienic design risk assessment workshop. Nine hours, online, self paced.