However, the report Bioaerosol emissions from waste comoposting and the potential for workers exposure highlighted that bioaerosols are substantially reduced at 50 to 100m distance downwind from the source when compared with its immediate area to 10m distance.
Results showed that close to the source of composting processes, large concentrations of bacteria, actinomycetes and fungi along with smaller amounts of endotoxin and dust, may become air-borne.
It was found if workers are not protected from the bioaerosols there is a 64% chance they will be exposed to 100,000 colony forming units per metre cubed (cfu/m3) of bacteria and a 28% chance of breathing in air in excess of 1 million cfu/m3 of bacteria. If a worker is protected by a vehicle cab this reduces considerably, with a 28% and 5% chance of exposure respectively.
At 50m distance the air sample bacteria concentrations dropped significantly with fewer than 1,000 cfu/m3. At a 100m to 250m distance, bacteria concentrations were reduced further and could be considered to be within the range of typical background levels.
Bioaerosols are airborne particles that are produced by living organisms, such as in the composting process. There is concern that workers on composting sites handling the compost at each stage may experience dangerous exposure to the particles. Previous studies have shown the possible link allergic respiratory ill health where bioaerosols are highly concentrated. Furthermore, people living or working near to waste composting sites may also be exposed to bioaerolsols.
The HSE has now designed a risk zone model, aiming to provide operators with a method by which they can assess the likelihood of bioaerosol exposure to workers depending on which zone they are working in. Red, amber and green zones demonstrate which areas onsite there is most exposure with red, the most and green the least.
Additionally, the research found that although it may be expected that in-vessel composting (IVC) systems would generate fewer bioaerosols because the compost does not need turning for aeration, this was not the case. In fact, IVC facilities were found to produce just as high levels of bioaerosol as open windrow sites.