Composting, the recycling of organic wastes such as vegetation and food waste, reduces the amount of waste going to landfill and is therefore a rapidly growing sector. The trade body the Renewable Energy Association (REA), formerly Association for Organics Recycling (AfOR), publishes a range of health and safety guidance for its members to include Health and safety at composting sites: A guide for site managers, which can be obtained as a priced publication from the REA.
Further information sources:
As a dutyholder you should take the health issues associated with bioaerosols into consideration, assess the risk and determine the control measures required, bearing in mind that:
Where your assessment has established that bioaerosol exposure may pose a potentially significant risk to the health of your workers:
Workers at waste management sites may potentially be exposed to a wide range of airborne organic and inorganic dusts, chemical and biological agents (the latter often referred to as bioaerosols), especially during tasks such as compost handling. To manage potential health risks from inhalation exposure there is a need to implement proportionate controls under COSHH. If workers are in enclosed vehicle cabs during waste handling, HSE funded studies have shown that this physical barrier should afford some protection from exposure to bioaerosols. However, a properly maintained cab air filtration system will be more effective. HSE provides advice for maintenance and testing of vehicle cab filtration systems in its COSHH Essentials guidance series (AG7; guidance for composting).
The guidance is based on ideal good practice and you should consider the following in the context of the operations you are carrying out:
Bioaerosols are naturally present in the air, mainly soil-borne micro-organisms in airborne dust, so everyone is constantly exposed to them and mostly they pose negligible health risk.
Concentrations change depending on the weather, season and whether indoors or outdoors. Typical bioaerosol concentrations are greater in rural areas, because of nearby vegetation, than in urban areas.
Bioaerosols can result from any process that makes microbially contaminated material airborne. Examples in the workplace include contaminated industrial process water. In agriculture, bioaerosol may be created from handling dusty contaminated material such as grain or animal feed, or from animal housing.
Because of the dilution effect in the open air, bioaerosol concentrations fall away rapidly with distance from compost being handled. It has been shown (RR786 - Bioaerosol emissions from waste composting and the potential for workers’ exposure) that by 100 to 200m away the bioaerosol concentration has mostly returned to background levels. Licensing and permitting of composting sites is by the Environment Agency (EA) in England and Wales and the Scottish Environment Protection Agency (SEPA) in Scotland.
Based on scientific evidence that bioaerosol levels from waste composting are reduced to background levels within 250 metres from source the EA in England and Wales currently operates a '250 metre limit' rule around composting sites to minimise the potential of bioaerosol exposure to nearby residents.
A ‘bespoke’ permit is required for facilities where the composting operations (open or contained) are within 250 metres of sensitive receptors. In such cases, the applicants will have to provide a site-specific bioaerosol risk assessment (SSBRA) which shows that bioaerosols from the composting operation can and will be maintained at acceptable levels at the sensitive receptors.
In Scotland, although SEPA do not have a stated position in the same way as EA, the issue of bioaerosols is a consideration when licensing sites.
Bioaerosols are always present in the atmosphere. These may be considered as the background level of exposure we constantly experience. The recent HSL study (2010) has confirmed previous published studies which showed that by 250m distance from composting activity in most cases the bioaerosol concentrations will be reduced to background levels.
In some studies, however, bioaerosol concentrations above background have been recorded. Consequently, although there is no evidence of ill health for nearby residents, it would be difficult to justify changes to the 250 metre limit set by the EA on the strength of current evidence. It should be noted that other activities locally, such as farming activities, or even the presence of large areas of vegetation, can also raise the background bioaerosol concentration.
It is recognised that bioaerosols are diluted and dispersed in the open air, so the risk is less for work further away from a bioaerosol source. A ‘risk zone’ approach therefore can be adopted to apply exposure controls proportionate to the likely level of bioaerosol exposure. The risk zone approach is summarised below: Full details an be found in the HSL study (2010) report.
Based on the results from this study, this level of exposure may be considered typical without a significant bioaerosol source nearby:
Red Zone - if you are working next to composting handling machinery and not protected within a vehicle cab:
Amber Zone - If you are working further away from composting handling machinery, and up to 50 metres from composting:
Yellow Zone - If you are working further away from composting handling machinery, between 50 and 100 metres from composting:
*Note that the experimental data appears to show higher potential exposure at 50 to 100m than at 50m, likely to be due to sample variability exaggerated by a small number of samples taken.
Green Zone - Nearer the site boundary, that is, 100 to 250 metres from composting:
If you work with compost, potentially you will be exposed to bioaerosols, because of the large number of micro-organism present in the compost. As with other workers exposed to organic dust and large numbers of airborne micro-organisms (e.g., in certain agricultural activities and in waste handling) if you breathe in those micro-organisms in large numbers over a long period they can trigger an allergic reaction. This can range from short term flu- like reaction (inhalation fever) to longer term ill health such as asthma or bronchitis. Once a person has become sensitised, subsequent exposure to even a smaller quantity can trigger the allergy.
The key is to assess risk and control exposure, which is an obligation, placed on employers by the Health and Safety at Work etc Act 1974 and other relevant statutory provisions such as the COSHH Regulations. Potential exposure can be controlled by changing the work process to minimise the generation of bioaerosols, or possibly by managing temperature and moisture levels in the compost to reduce dustiness. Introducing control measures may also be applicable, such as exhaust ventilation to prevent exposure, using adequate filters on the air intakes of vehicles such as tractors used to move compost, or using personal protective equipment such as adequate and suitably fitted respiratory protective devices when working in areas close to where bioaerosols are generated.
The greatest risk of exposure, justifying the control measures described above, are when in close proximity to compost being handled i.e. within 30 metres. Further away when working outside exposure levels will be greatly reduced and require less stringent control, but may still be above background levels. If site specific measurements indicate elevated bioaerosol levels beyond 30 metres then it may be appropriate to provide respiratory protection especially if working in those areas for extended periods.
In more traditional composting, the material is composted outdoors in heaps (open windrows) that are turned frequently to aerate the compost and it is this turning process that generates most bioaerosols. In some composting systems known as in-vessel composting systems (IVC), also used to compost material potentially containing animal by-products, the composting process is enclosed and sometimes uses forced aeration, but the material is not turned. Bioaerosols will still be generated particularly when the material is being handled to load and unload the vessel, and during post-vessel maturation of the compost.
At some sites, composting may be done in enclosed facilities. While this may reduce bioaerosol emissions downwind to comply with EA permit conditions if the facility is within 250 metres of a sensitive receptor, the enclosure may increase bioaerosol concentrations to which workers are exposed by reducing the potential for open air dilution and dispersion of emissions, including bioaerosols. In such cases, operators should ensure that suitable ventilation systems (forced or otherwise) are provided that ensure suitable dilution of bioaerosols and biogases such as carbon dioxide (as well as provision of sufficient oxygen). Monitoring of contaminants such as bioaerosols and carbon dioxide will demonstrate if control systems are effective.
Even if you can smell a compost site you might not be exposed to bioaerosols. Composted material can have a distinctive smell, depending on the feedstock, for example if it contains a large proportion of pine branches there will be the characteristic resin smell. The chemicals responsible for smells are gases, which are smaller and lighter than particles of dust and bioaerosols and therefore can travel further in the air. Also, some odorous gases can be smelled at extremely low concentration.
Bioaerosols are always present in the atmosphere. These may be considered as the background level of exposure we constantly experience.
Most published studies on compost bioaerosol exposure and health have focussed on the exposure of workers on sites handling the material, because their exposure will be greatest. Some studies have looked at the effect of composting activities on surrounding bioaerosol concentrations. A limited number of studies have looked at the health of nearby residents. While it is recognised from these studies that under certain conditions composting activities nearby may raise bioaerosol concentrations above background levels, these concentrations are much lower than would occur on a composting site near to compost material being handled. There is no reported evidence of significant increase in ill health in residents near composting sites in these situations. The lungs of a healthy person are capable of being exposed to relatively large concentrations of micro-organisms without ill effect.
The recent HSL study (2010) has confirmed previous published studies which showed that by 250m distance from composting activity in most cases the bioaerosol concentrations will be reduced to background levels.
Complainants regarding smell and other public nuisance issues should be made to to the appropriate local authority Environmental Health Department or EA (or SEPA in Scotland).
In addition to the hazards associated with inhalation of bioaerosols on composting sites, there may be other biological hazards depending on the feedstock. If sewage sludge is being used, there may be infectious bacteria and viruses present. If vermin on the site are not controlled, there is the risk of workers contracting leptospirosis (Weil's disease), a bacterial infection caused by exposure to contaminated rat urine. Good hygiene, including provision of adequate hand washing facilities, can reduce these risks.
In enclosed buildings, other hazards include the build-up of biogas (carbon dioxide, hydrogen sulphide etc.) from the biodegradation process and exhaust gases from the mobile plant and delivery and collection vehicles. If these are allowed to build up sufficiently they may cause an asphyxiation hazard. Increased dust and volatile organic compounds (VOCs) exposure, potential thermal discomfort from excessive heat and humidity, poor visibility due to high moisture content in the atmosphere and odour may also result in enclosed buildings.
It is the responsibility of the site operator to identify potential hazards, make a suitable risk assessment and to provide adequate protection to their work force to control such risks.
Also see Frequently Asked Questions on the Health Protection Agency website