Hygienic Design for Washdown Computers and Monitors

Hygienic design is the practice of building equipment so that it cannot harbour soil or bacteria and can be cleaned quickly and completely. For a washdown computer or monitor, that means a smooth, sealed stainless steel housing with no crevices, a flush glass front, sealed connectors and an ingress rating, usually IP69K, that survives high-pressure, high-temperature cleaning every shift.

Hygienic design is called sanitary design in North America, and it is set out in the guidelines of EHEDG, the European Hygienic Engineering and Design Group, in European standards such as EN 1672-2 and EN ISO 14159, and in the 3-A Sanitary Standards and NSF standards in the US. Most of that guidance was written for equipment that touches food. Computers and displays rarely do, but they sit in the splash zone, are hosed and foamed with everything around them, and can drip residue back onto the line if they hold it.

This guide explains the principles and standards, the food, splash and non-food zones, what a washdown computer has to survive, IP69K sealing, stainless steel grades and seal materials, touch screens, the details we check on every washdown panel PC and monitor, and how to choose one for a food and beverage line.

Several bodies publish hygienic design rules, and a food plant’s engineering specification may quote any of them. The table sets out the ones most often named, what they cover and what they mean for a computer or display on the line.

EHEDG and 3-A both offer certification, but mainly for equipment that contacts product, such as valves, pumps and fillers. Computers and displays are rarely certified by either, so a specification for an HMI usually asks for design to the principles, a tested ingress rating, and stainless steel and seal materials that suit the cleaning chemistry. That is the approach this guide follows.

Both aim at the same result, equipment that can be cleaned to a microbiologically safe level, but they come from different places and work differently.

Food companies with plants on both continents often reference both. For a computer or display the practical outcome is the same set of features: smooth stainless surfaces, no crevices, sealed joints and connectors, and materials that tolerate the cleaning chemicals.

EN 1672-2 divides machinery surfaces into three zones according to their risk of contaminating food. The zone a computer or display sits in decides how strict its hygienic design needs to be.

In practice the splash zone is where hygienic design pays off. A panel PC on an arm next to a cutting line will be sprayed with water carrying fat and protein, foamed, rinsed and sanitised. If its housing has a ledge, a gap behind a bezel or a screw head, residue lodges there and becomes a place for bacteria to grow, and the next rinse can carry them back to the line. Our washdown area explainer describes the space itself.

Washdown is the open-plant cleaning that happens at the end of a shift or a production run. A typical sequence, following the steps the NSF summarises for food plants, looks like this:

1. Dry clean. Remove debris by hand, brush or scraper.
2. Pre-rinse. Warm water, typically below 50 °C so proteins do not bake onto surfaces.
3. Foam. Alkaline foam to lift fats and proteins, with an acid descaler where water is hard.
4. Rinse. Hotter water to remove every trace of detergent.
5. Inspect. Check corners, seams and fixings where soil hides.
6. Sanitise. Chlorine-based, peracetic acid or quaternary ammonium sanitisers.
7. Dry. Usually air drying, helped by the heat left from the rinse.

Every one of those steps lands on the HMI. The housing sees hot water, repeated thermal shock, caustic and acidic chemistry and, often, a pressure washer held a few centimetres from the seals. Enclosed process equipment is cleaned differently, by clean in place (CIP), where cleaning solutions are pumped through pipework and tanks without opening them. The HMI that runs a CIP cycle is still washed down on the outside.

The chemistry of a cleaning regime matters as much as the water pressure. Each class of chemical attacks different materials, so the hygiene team’s chemical list belongs in the specification of every washdown computer.

Seal materials are the usual weak point. EPDM, silicone and fluoroelastomer (FKM) seals each tolerate a different range of chemicals and temperatures, and food plants often prefer seals made from materials that comply with food contact rules. Ask the manufacturer which compound is used and check it against the chemical supplier’s compatibility chart.

An ingress protection rating tells you what an enclosure has been tested against. For washdown, three ratings matter, and our IP rating chart covers every level.

IP69K is the only one of the three that matches close-range, hot, high-pressure cleaning, which is why it has become the default for HMIs on open food lines. Many washdown systems carry IP66 and IP69K together, because the two tests cover different things, and our comparison of IP69K vs IP67 explains why the immersion rating does not cover jets. A front-only rating such as front IP65 protects a panel-mount display from the operator side only, so the rear must sit inside a sealed cabinet. The IP69K FAQ summarises the test.

Stainless steel is the standard housing for washdown equipment because it resists corrosion, takes a smooth finish and tolerates the chemicals used in food plants. Two grades cover almost every washdown HMI. Grade 304 contains around 18% chromium and 8% nickel and suits most food, bakery and packaging areas. Grade 316 adds 2 to 3% molybdenum, which improves resistance to pitting from chlorides: the chlorine in sanitisers, brines and salt.

As a rule of thumb, choose 316 where chlorinated sanitisers are used every shift. The extra cost is small against a housing that pits and harbours bacteria. Whichever grade you choose, keep the finish smooth: abrasive pads scratch the passive layer that protects the steel. Our comparison of 304 and 316 stainless steel goes further, and food grade stainless steel explains what the term does and does not guarantee.

The North American Meat Institute’s ten principles of sanitary design are among the most widely quoted summaries of hygienic design, and they sit comfortably alongside the EHEDG guidelines. They were written for processing equipment, but each one translates to a washdown computer or display.

Principles 4, 5 and 6 are where most standard panel PCs fall short. A bezel that sits proud of the glass, a recessed screw or a gap behind a cable gland is enough to fail them, however good the ingress rating.

The screen is the part of a washdown HMI that operators touch most and cleaners spray hardest. Projected capacitive (PCAP) touch sits behind a single sheet of flush glass, so there is no film or bezel edge to lift or trap residue, and controllers tuned for water rejection ignore droplets left after a rinse. Resistive touch still has a place where operators wear thick work gloves, and our guide to touch technology compares the two.

Hot rinses followed by cold production air can fog the inside of a display. Optically bonded screens fill the gap between the glass and the LCD, removing the air layer where condensation forms and improving readability under bright factory lighting. Arestech’s TPM-3621PW-B6A1 monitor, for example, has a touch on/off button so staff can switch touch off while the screen is wiped or sprayed.

Having supplied panel PCs and displays into washdown areas for many years, we see the same weak points again and again. Cable entries and standard connectors let water in long before a sealed housing does, which is why sealed M12 connectors matter as much as the rating on the front. Buttons, antenna housings and speaker grilles add seams; a flat antenna cover and a touch screen in place of buttons remove them.

Seals are the other wear item. Repeated thermal shock and strong chemicals harden gaskets over time, so check them at planned maintenance, follow the chemical concentrations your supplier recommends and avoid holding a pressure lance on a seal from point-blank range for longer than the clean needs.

Some IP69K enclosures include a pressure equalisation vent, which lets the enclosure breathe as it heats and cools without drawing in water. Preventing condensation covers the other options.

Environment. Start with the cleaning regime: how often, how hot, what pressure and which chemicals. That sets the ingress rating, usually IP69K, and the steel grade.

Performance. Match the processor and screen to the software: a line HMI, a SCADA client, a recipe station or a vision system each need different compute and display sizes.

Expansion. List the devices the computer must connect to, from barcode scanners and scales to PLCs, and make sure every port is sealed, whether through M12 connectors, PoE or wireless behind a sealed antenna.

Lifecycle. Food lines run for years. Choose a model with long availability and replaceable seals so a failed system can be swapped like for like.

Browse our stainless steel panel PCs, stainless steel monitors and IP69K computers, or see how we support food and beverage manufacturers. Our case study on waterproof HMIs for food and beverage manufacturers shows the approach in practice. For particle-controlled production rather than wet cleaning, read our guide to clean room computers.

The systems below are designed for washdown in their manufacturers’ specifications. As your system integrator we configure and test every system before it ships, imaging the panel PCs with your operating system and software; monitors are configured and tested. Sealing ratings and steel grades are the manufacturer’s, and we confirm them for the exact model and options you order.