Table I.

Advantages and disadvantages of different airflow visualisation techniques

Technique	Advantages	Disadvantages
Real approaches:
Human volunteers	Realistic subjects and physiology, particularly with regard to thermal characteristics and thermal boundary layers	Safety is important. Human volunteers cannot be exposed to high intensity (e.g. laser) light or irritant or toxic tracer gases or particles
Hospital monitoring	Realistic situations and environments	Highly variable results, often obtained using non-standard techniques, making interpretation difficult, and therefore limiting any useful generalisation
Theoretical approaches:
Computational fluid dynamics (CFD)	Good spatial/temporal information. It is a standard modelling tool in the industry	Difficult to model moving bodies. Difficult to obtain accurate simulations due to required computing power and/or simulation time
Abstract approaches:
Physical analogues in scale model or in full scale (models)	Quick and relatively easy to build with reasonable spatial resolution. Able to test different hypotheses related to flow patterns in different geometries using a variety of flow-generating techniques/devices. Easy to work with tracer gas and airborne particles for the simulation of viruses and bacteria in full scale experiments with thermal mannequins	Difficult to combine different contributions to bulk air flows in small scale, and difficult to work with movements of persons in full scale