Designing an emergency department involves more than deciding how many rooms it needs and how large they should be.

Patients arrive, are assessed, wait, receive treatment, undergo diagnostic tests and eventually leave or move to another hospital unit. Each step requires space, resources and a connection with what happens next.

Hospital design guidelines help translate these needs into a functional programme. They provide recommendations for planning, sizing and organising the spaces required to deliver care.

Spain’s Ministry of Health published its Standards and Recommendations for Hospital Emergency Units in 2010. The Australasian Health Facility Guidelines also provide planning guidance for emergency units, including functional configurations and activity flow diagrams.

These documents are essential starting points. But an important question remains: how can we assess whether a proposed design will work under the conditions the department is likely to face?

A functional programme may specify the expected number of treatment bays, observation spaces, waiting areas and support rooms. A floor plan can show their location and how they connect.

Yet neither document, on its own, tells us how the department will behave when several patients need the same resource at once, treatment takes longer than expected, or patients cannot move to the next stage of care.

Consider a treatment bay occupied by a patient who is ready to leave the emergency department but is waiting for an inpatient bed. The bay still exists. Its dimensions have not changed. But it cannot receive another patient until the current one moves on.

The consequences may extend beyond that single space. A new arrival may have to wait for a bay, increasing pressure elsewhere in the department.

The design has not changed, but the department’s effective capacity has.

This distinction matters when planning new facilities or refurbishing existing ones. Meeting spatial requirements is necessary, but it does not automatically demonstrate that the resulting configuration will support an effective patient journey.

In my Master’s research in Hospital Engineering and Architecture, I developed the DFU simulation model to explore how changes in demand, resource availability, patient characteristics and process times affect emergency department operational capacity.

By changing selected parameters while keeping others constant, the model allows different scenarios to be compared. This provides a way to investigate how the same physical resources may perform under different operating conditions.

The approach does not replace design standards, clinical judgement or the experience of healthcare professionals. Nor does a simulation alone establish that a proposed design will work in practice. Its value is to help identify questions and test assumptions before decisions about the physical environment are finalised.

For example, planners can ask not only how many treatment bays are required, but also how long they may remain occupied, what happens when downstream resources are unavailable, and whether the proposed arrangement supports the movement of patients between stages of care.

These questions connect architectural decisions with operational performance.

A functional programme tells us which spaces a department needs. Analysing the patient journey helps us examine how those spaces must work together.

For hospital planners and engineers, both perspectives are essential. Good design is not simply about providing the right rooms. It is about creating an environment that can support the processes patients and professionals need to carry out.