Why write a dictionary of chemical engineering practice? Engineers unfortunately use the same words to mean different things, and different words to mean the same things.

I’ll give a specific example – In the context of engineering design (especially process design), does “hygienic” mean the same as “sanitary”? Are they almost the same? Or are they entirely different? It depends who you ask (those of you who don’t like words can skip to the end where I discuss practical implications of this)

I have in my library a book called “Modern Sewage Disposal and Hygienics” from 1930 (everything was supposedly “Modern” in 1930, though its introduction’s opening line is rather less than modern):

What of this book? Although essentially for men, it is for women too…

So, “Hygienics” used to be to do with sewage treatment, as was “sanitary engineering”, though these words are rarely used in the modern (as opposed to “Modern”) industry. Conventional dictionary definitions still however link them closely, and link both words to sewage. The Cambridge Dictionary defines them as follows:

Sanitary:

” clean and not dangerous for your health, or protecting health by removing dirt and waste, especially human waste”

Hygienic:

clean, especially in order to prevent disease:

So do these words mainly mean “clean”, possibly including measures taken to exclude human waste from a product? In my experience, these words are more important in food and pharmaceutical plant design than they are in sewage or potable water treatment. In industries effectively regulated by the US FDA, (the food, beverage, and pharmaceutical industries) the words are arguably highly interchangeable. In the dairy industry for example, the US has its “3-A Sanitary Standards”, and over here we have the “European Hygienic Engineering and Design Group Guidelines”. Both are ultimately intended to address the FDA’s requirements so that products can be sold in the US, and places such as China who have food and drug safety rules modelled on the US FDA.

If we look up “Hygienic Design and Engineering” in the EHEDG glossary, we get

Design and engineering of equipment and premises assuring the food is safe and suitable for human consumption.

If we look up what they mean by “Hygienic”, they send us to “Food Hygiene”, where they quote the European Codex

All conditions and measures necessary to ensure the safety and suitability of food at all stages of the food chain

 So they are primarily concerned about food, and clearly have a wider concerns than keeping food free of sewage.

They say nothing about the word “sanitary”, but discuss “Sanitation” – Sometimes used in place of hygiene”, “Sanitization (USA) – in summary the Codex prefers disinfection” , and “Sanitizer (USA)- Codex prefers disinfectant”. So is “Sanitary” simply an Americanism, as the EHEDG’s inserting (USA) around related terms implies? Perhaps so, though it would have been helpful of the EHEDG glossary to spell this out rather than imply it. They are a bit vague.

Neither is it quite this straightforward, as the US equivalent of the EHEDG , the National Sanitation Foundation publish something called the NSF/3-A/ANSI 14159-1 Hygiene Requirements for the Design of Meat and Poultry Processing Equipment developed in collaboration with 3A. The NSF also seem to believe that hygiene is to some extent interchangeable with “Sanitation” (which to me is something written on the side of a “garbage truck”).

The EHEDG, NSF and 3A are looking to harmonise their standards, so this will hopefully all get sorted out. There are still however some seemingly minor differences in interpretation of these standards which can have large practical implications for designers which I will cover shortly.

So it may be that the English speaking international food industry isn’t so far apart as it would seem at first glance, and is getting ever closer. What of the pharma industry? It is also seeking to satisfy FDA requirements, and increasingly (I am told) uses the EDEDG guidelines as well as others such as the ISPE’s and ASME BPE) approaches to assure/ensure product safety. (BTW, the ASME BPE guidance on this subject? “sanitary: see hygienic”)

The ISPE also produce a glossary. It’s a lot bigger than the EHEDG’s and defines hygienic design very differently:

A system of design that meets standards, specification, codes, regulatory and industrial guidelines, and acceptable engineering design methods to reach a degree of sanitation required by food, pharmaceutical, and cosmetics processing.

That’s a lot wider than the EHEDG’s definition, and seems to me to evoke good engineering practice. What do they mean by “Hygienic”? –

Of, or pertaining to, equipment and piping systems that by design, materials of construction, and operation provide for the maintenance of cleanliness so that products produced by these systems will not adversely affect human or animal health.

I think the ISPE definitions are simply better than the EHEDG’s. They are more explicit, and flag the key elements required to address them in design. They also define “Hygienic Tubing system” as

Systems that provide for the maintenance of cleanliness so that products transferred and/or conveyed through them will not have their identity, strength, quality, purity, or potency compromised

This is useful stuff. How about “Sanitary Design”? The ISPE glossary says:

A misnomer for “Hygienic Design”. The term Sanitary Design is no longer in use by the industry in the context of this definition.

Oh-oh! Sanitary is not an alternative word choice according to the ISPE. It’s just plain wrong.

This is an example of the speciation of words and concepts I have noted previously. Words can separate in meaning over time until they mean different things in different areas.

This is where things get practically problematic in hygienic design. Let’s get very specific and practical. Neither glossary defines what constitutes a hygienic or sanitary valve, and I think that there is a good reason for this. Hygienic design is a whole-system property, as the ISPE definitions make clear. System components need to be selected towards this aim, but they cannot ensure it.

There appear to be differences in opinion between practitioners in food and pharma, the US and elsewhere about which kinds of valves “are” sanitary / hygienic. The most contested type is the “double seat mixproof valve” which various manufacturers claim to have invented quite recently.

This is a clever bit of kit, but it was invented in the dairy industry, so many pharma (especially biopharma) people don’t trust it on the NIH principle. If they want a double block and bleed arrangement functionally similar to that provide by the mixproof valve, they might use an arrangement of zero deadleg diaphragm valves.

Conversely, there are those in the dairy industry who consider mixproof valves of one sort or another (there are many subtypes) to be more or less the only “hygienic valves”, (and a panacea), and zero deadleg valves not properly hygienic.

Both arrangements are claimed to be “hygienic”, both are allowed by EHEDG and ISPE guidelines, but differences of opinion can cost a lot of money here. Let’s not even get into whether there is such a thing as a hygienic butterfly valve….

Words matter for engineers, whether they like it or not.

Books by Sean Moran

Process Plant Layout

An Applied Guide to Water and Effluent Treatment Plant Design

An Applied Guide to Process and Plant Design

An Applied Guide to Process and Plant Design, 2nd Edition

All titles are available on ScienceDirect. Want your own copy? Enter code STC320 when you order via the Elsevier store to save up to 30%

About the Author

Professor Moran is a chemical engineer, chartered engineer, chartered waste and environment manager with twenty-five years’ experience in process design, commissioning and troubleshooting. He started his career with international process engineering contractors and worked worldwide on water treatment projects before setting up his own consultancy in 1996, specializing in process and hydraulic design, commissioning and troubleshooting of industrial effluent and water treatment plants. Sean was until 2015 an Associate Professor at the University of Nottingham, where he coordinated the design teaching program for chemical engineering students. He has now returned to engineering practice, specializing in forensic engineering in commercial disputes centering on plant design issues.