Circulation & Segregated Flows

To plan circulation you first have to see it as several distinct flows, each with its own needs, sharing one building.

Patients move in several modes: ambulant outpatients walking in; inpatients wheeled on beds between wards, imaging and theatres; emergency patients arriving acutely. Bed and trolley movement needs wide corridors, generous lifts and gentle level changes, and it should be kept away from public crush and from undignified exposure.

Staff need fast, direct, often private routes between the departments they shuttle between - sometimes back corridors and dedicated lifts that bypass the public entirely, saving steps on journeys repeated hundreds of times a shift.

The public - visitors and outpatients - need a clear, welcoming, legible route from the entrance to their destination, and they must be gently contained: able to reach wards and clinics, kept out of clinical and service zones.

Supplies flow inward: sterile instruments from CSSD, drugs from pharmacy, clean linen, food, consumables, all ideally on back-of-house routes the public never sees.

Waste and dirty flows move outward: clinical and general waste, used instruments, soiled linen, and the deceased to the mortuary - the 'dirty' flows that must be kept off clean and public routes.

> A hospital corridor is never neutral - it is always carrying one of these flows, and the question is always: which flows meet here, and should they?

The reason a hospital looks so complex from outside - multiple entrances, separate lift cores, service basements, double corridors - is almost entirely the physical expression of keeping these flows distinct. Once you can name the flows, the apparent complexity resolves into a logic you can read and design. A useful habit is to give each flow a colour and trace it across the plan as a continuous line, from where it enters the site to where it leaves: the moment two lines that should never touch cross on your drawing, you have found a problem to solve before it is built. The flows also differ in volume and rhythm - the public surges at visiting hours, supplies arrive in scheduled deliveries, emergencies are unpredictable - and a plan that ignores those patterns creates bottlenecks even when the routes themselves are correctly separated.

Of all the flow rules, one stands above the rest because it is a matter of infection and therefore of life: the separation of clean and dirty. Sterile and contaminated paths must never cross. The clearest worked example is the operating-theatre suite. Sterile instrument sets prepared in the central sterile services department travel to theatre along a clean supply route; after surgery, the used, contaminated instruments and the clinical waste leave by a separate dirty return, back to CSSD's decontamination side and to waste disposal. If those two routes cross - if a dirty trolley and a sterile set share a corridor or a lift - the separation is broken and the infection risk is real.

The same logic repeats across the hospital. Clean linen and soiled linen travel and are stored separately. Food delivery and waste collection use different routes and never the same lift. An infectious patient is moved so as not to expose others, which is why isolation rooms and their circulation are planned with care (Module 5). The principle is sometimes organised as one-way flow through a department - entering clean, leaving dirty, never doubling back - so that contamination cannot travel upstream.

This is also where infection control becomes spatial rather than merely procedural. Hand hygiene, cleaning and protocols do enormous work, but the building either helps or fights them. A plan that forces staff to carry waste back through a clean corridor has designed a daily infection risk that no protocol can fully cancel. The designer's job is to make the clean route the natural, easy, default route and the dirty route a separate, contained one - so that doing the safe thing is also the convenient thing. The specific regimes - which spaces are 'clean', the pressure and air requirements that reinforce separation - are engineering and infection-control matters to verify against the current standards and your specialists (Module 5.2), but the planning move belongs here, in circulation.

Within a floor, flows are carried by horizontal circulation - corridors, the hospital street, and ward layouts - and the way these are arranged either keeps flows apart or forces them together.

The simplest device is separate corridors for separate flows. A department may have a public/patient corridor on one side and a staff/supply corridor on the other, so that clean supply and dirty return, or staff and public, do not share a route. The racetrack ward, introduced in Lesson 1.1, is a refined version of this: a double-corridor loop around a serviced core, where one corridor can serve the public and patient rooms and the inner zone handles clinical support and dirty utilities. The hospital street - a top-lit public spine with departments branching off it - carries the main public and patient flow while allowing each department to keep its own back-of-house routes off the street.

Corridor design carries real clinical weight. Widths must let two beds pass and allow a bed to turn into a room; the brief will call for generous dimensions that you verify against the current code, never assume. Long corridors need rest points, handrails, daylight and clear wayfinding, because frightened and unwell people travel them. Dead-end arrangements that trap flows, or single corridors forced to carry everything at once, are the classic failures. And corridors double as refuge and escape in a fire, where non-ambulant patients cannot simply run out - so circulation is also life-safety, a theme Module 7 develops and which you should design for from the first corridor.

The test to apply to every horizontal route is simple and relentless: which flows use this corridor, and is it acceptable for them to meet here? If clean and dirty, or public and clinical, are forced together, the plan needs another route - not a sign telling people to behave.

In a multi-storey hospital, separation is as much a section problem as a plan problem, and it is solved with differentiated lift cores. A single bank of lifts carrying everyone and everything - beds, staff, visitors, meals and waste together - is a classic planning failure: it mixes clean and dirty, delays emergencies behind visitor traffic, and undignifies patients. Instead, a well-planned hospital provides separate vertical circulation for different flows, typically something like: public/visitor lifts; bed or patient lifts (large, for a bed plus attendants and equipment); and service lifts for supplies and waste - sometimes with clean and dirty service lifts kept distinct, or timed and cleaned between clean and dirty loads.

The number, size and grouping of lifts are planning and engineering decisions - driven by the bed count, the traffic analysis and the current code - and are exactly the kind of figure to verify rather than assume. But the principle is fixed: the vertical cores must carry the horizontal flow separations up through the building, so that clean and dirty, public and clinical, stay apart on the journey between floors just as they do along the corridors. Stairs, firefighting lifts and protected shafts add the life-safety layer.

Vertical circulation also expresses the adjacency logic of Lesson 1.2 in section. A dedicated bed-lift connecting the emergency department on the podium to the intensive-care unit and theatres can make a vertical adjacency behave almost like a horizontal one - collapsing the clinical chain even when departments cannot share a level. Conversely, a hospital whose cores are badly placed or undersized turns every inter-floor journey into a bottleneck.

Put the horizontal and vertical together and you have the hospital's full circulation system - a three-dimensional network of segregated flows. It is the connective tissue that makes the departments of Lesson 1.2 work as one organism, and it must sit on the disciplined grid of Lesson 1.4 so that the cores and corridors line up floor to floor and the whole thing can still change over time.