There are many different mathematical models for transmitting infections in enclosed rooms. These models try to capture various transmission conditions: the number of people in the room, how many are healthy and how many sick, whether they are talking or shouting, whether they are in the room only briefly or all the time, how many infectious viruses they emit into the space in a given time unit, what the distances are between them and many other parameters. Surely it is clear to everyone how many different results are possible. Of course, these models are of great practi-cal importance and need to be further worked on and improved.

What is not entirely correct, however, is to state the effectiveness of disin-fection units and to refer in small print to the connection with some model of the spread of infections. The reasons are as follows:

It is difficult for a layman to determine which disinfection unit is better if one of them reports a 90% reduction in the risk of disease in a given room per hour, with an 80% reduction in disinfection efficiency per pass and the other reports a 70% reduction in disease risk per hour in the same room with a disinfection efficiency of 99.99% per pass. Each has the same air flow through the disinfection unit. Improving the disinfection efficiency in the first case can be easily achieved by a suitable choice of mathematical model.

So which disinfection unit is better? It is the one that has higher disinfec-tion efficiency in a single pass through the disinfection unit for a given test virus or bacteria in the same air pass.

If the disinfection efficiencies are the same, what other properties and parameters are crucial for selection?

It is necessary to find out whether the disinfection unit ensures the flow of air in the whole room or if there is a short area of air flow only in its vicinity.

It is necessary to know the following parameters: total power consump-tion, life of UV lamps, the possibility of flow control, equipment noise for different air flows, the possibility of remote control. Of equal importance, the design of the device and its flexibility to adapt to the given interior are also decisive.