The degree of risk from microbial contamination of manufactured products by sources of
contamination in healthcare cleanrooms has been assessed in a series of three articles. This first
article considers airborne sources, and a second article will consider surface contact and liquid
sources. A final article will consider all sources and the application of the risk method to a variety of
cleanroom designs and manufacturing methods.
The assessment of the degree of risk from airborne sources of microbial contamination has been
carried out by calculating the number of microbes deposited from the air (NMDA) onto, or into, a
product from various sources. A fundamental equation was used that utilises the following variables
(risk factors): concentration of source microbes; surface area of product exposed to microbial
deposition; ease of microbial dispersion, transmission and deposition from source to product; and
time available for deposition. This approach gives an accurate risk assessment, although it is
dependent on the quality of the input data. It is a particularly useful method as it calculates the likely
rate of product microbial contamination from the various sources of airborne contamination
