Composting - Recycling biodegradable waste

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.

Health and safety at composting sites: A guide for site managers

Main injury risks

Transport, including vehicle movements, falls during sheeting operations, poor site layout and control, reversing and visibility issues. There is a risk of collisions if moving plant/vehicles and pedestrians are not adequately segregated.
Machinery, including system failures to control the risks associated with shredders, conveyors and bagging operations.
Slips and trips, including failure to control material spillages.

Occupational ill-health concerns

Musculoskeletal injury from manual handling.
Dermatitis caused by poor handling practices and inadequate welfare facilities.
Bioaerosols from Composting: Composting is a natural process in which micro-organisms (fungal/mould spores such as the fungus Aspergillus fumigatus and certain types of bacteria called actinomycetes) are encouraged to grow to break down waste material, resulting in very large numbers of these micro-organisms being present in the compost. Any handling of the material that generates dust will create a bioaerosol (micro-organisms made airborne). Commercial scale composting is done either in open windrows (long heaps of composting material) or in-vessel systems (where the composting material is enclosed; a requirement for treating material containing animal waste). To encourage efficient composting, the material has to be well aerated. Aeration of open windrows is by regular turning of the material, which will create bioaerosols. In-vessel systems usually have forced air ventilation which is less likely to create bioaerosols. However, at the end of either process often the compost is screened (sieved) to produce a quality soil supplement and this could create bioaerosols.
What are the health issues?
What do you need to do?
Effective use of vehicle cab air filtration systems on waste sites
What are the risks to others?
Risk Zone approach
Other frequently asked questions (FAQs)

Further information sources:

Information about the public health risks associated with composting and bioaerosols is available on the Health Protection Agency web site. Here a series of questions and answers addresses in more detail health risks, site boundary issues, odour and associated regulations, including those from the Environment Agency (EA).
Site licensing requirements are available from the EA and SEPA web sites.
The trade body the Renewable Energy Association (REA), formerly Association for Organics Recycling (AfOR), has produced a safety guide designed to help minimise the health and safety risks on composting site. Aimed at composting site operators, it includes advice on reducing health problems caused by airborne micro-organisms (bioaerosols). Health and safety at composting sites: A guide for site managers is available from the REA as a priced publication.

What are the health issues?

Repeated inhalation of compost bioaerosols in large concentrations has been shown to trigger the immune system, and could lead to developing asthma or extrinsic allergic alveolitis (similar to farmer's lung disease) (HSE funded research; Defra funded research).
HSE funded research has shown that workers in close proximity to waste composting processes could be exposed to bioaerosols between 10 and 1,000 times greater than in ambient air (see also risk summary below Risk zone summary).
Compost bioaerosols are a substance hazardous to health as defined by the Control of Substances Hazardous to Health Regulations (COSHH) 2002 (as amended). Although they have no occupational exposure limits, they are potential respiratory sensitisers. Regulation 7(1) requires that exposure to substances hazardous to health is prevented or, where this is not reasonably practicable, adequately controlled. A similar principle has been applied to poultry dust.
Health Protection Agency – Frequently Asked Questions (FAQs)

What do you need to do?

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:

Identify areas of your waste handling facility where bioaerosols are likely to be greatest.
Identify processes or activities that are most likely to create bioaerosols (for example, turning actively composting material, screening composted material) – don't forget that equipment maintenance may create aerosols as well.
Consider local conditions that might increase bioaerosol exposure, for example, weather conditions that might increase exposure and when certain activities could be avoided if that is practical.
Identify the workers that will be involved in the above activities.
It is likely that such a risk assessment may require the routine use of respiratory protective equipment (RPE) so workers can avoid exposure to bioaerosols when shredding, turning, screening or moving composting material or whenever leachate is either sprayed or transferred from one place to another. This precaution is likely to be required by anyone within 30 metres of such a procedure, and for five minutes afterwards. HSE's guidance HSG53, in particular Appendix 2 which deals with biological agents, will help with regard to the choice of RPE. Suitably fitted RPE of P2 or P3 filtration is suitable for use against biological agents in terms of non-penetration of spores/cells through the filter material.
For those working within a vehicle cab, with an adequate, well maintained, filtration system then RPE may not be needed, but you would need to demonstrate the effectiveness of the cab filter and a proper system of work such as ensuring staff keep their cab doors and windows closed.

Effective use of vehicle cab air filtration systems on waste sites

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:

When choosing a vehicle for use on dusty waste management sites, opt for one with a cab air filtration system already fitted if possible, or consider retro-fitting one.
Air intakes for cab filtration systems should be away from dust sources so that the filters clog less quickly.
Plan a maintenance schedule of filter removal, cleaning or replacement, the frequency of which is dictated by the dustiness of the conditions in which the vehicle is used. The schedule should also include visual examination for wear and tear damage to door and window seals. A check list could be used to provide instructions.
Remind staff of the importance of keeping doors and windows closed in the dustiest areas and regular cleaning of cabs to prevent dust build-up inside, and to report any signs of dust leakage.

What are the risks to others?

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.

Risk Zone Approach

How far away from composting activity so not to be exposed to bioaerosols?

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.

A 'Risk Zone' approach to control of exposure to bioaerosols (extracts taken from Research Report RR786)

Based on the results from this study, this level of exposure may be considered typical without a significant bioaerosol source nearby:

An 11% chance of being exposed to more than 1,000 cfu airborne bacteria but unlikely to be exposed to more than 5,000 cfu;
A 16% chance of being exposed to more than 1,000 cfu airborne fungal spores but unlikely to be exposed to more than 5,000 cfu;
Unlikely to be exposed to more than 1,000 cfu airborne Aspergillus fumigatus spores.

Red Zone - if you are working next to composting handling machinery and not protected within a vehicle cab:

A 64% chance of being exposed to more than 100,000 cfu bacteria (therefore more than 100 times the background level) and a 28% chance of being exposed to more than 1 million cfu bacteria (therefore more than 1,000 times the background level);
A 24% chance of being exposed to more than 100,000 cfu Aspergillus fumigatus fungus spores (therefore more than 100 times the background level) and a 4% chance of being exposed to more than 1 million cfu/m3 Aspergillus fumigatus spores (therefore more than 1,000 times the background level).

Amber Zone - If you are working further away from composting handling machinery, and up to 50 metres from composting:

A 6% chance that exposure to airborne bacteria will be greater than 5,000 cfu (5 times background level) and 36% chance of it being greater than 1,000 cfu (approximately three times more likely to be exposed to the highest background levels);
A 6% chance that exposure to airborne Aspergillus fumigatus spores will be more than 5,000 cfu (5 times higher than background level) and 21% chance that exposure to airborne Aspergillus fumigatus spores will be more than 1,000 cfu (that is, a 21% chance of exposure being greater that highest background levels).

Yellow Zone - If you are working further away from composting handling machinery, between 50 and 100 metres from composting:

No samples of airborne bacteria were greater than 5,000 cfu and a 34% chance of exposure being greater than 1,000 cfu (approximately three times more likely to be exposed to the highest background levels);
A 12% chance that exposure to airborne Aspergillus fumigatus spores will be more than 5,000 cfu (5 times higher than background level) and 34% chance that exposure to airborne Aspergillus fumigatus spores will be more than 1,000 cfu (that is, a 34% chance of exposure being greater that highest background levels)*.

*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:

A 7% chance that exposure to airborne bacteria will be greater than 5,000 cfu (5 times background level) and 18% chance of it being greater than 1,000 cfu (compared to an 11% chance of greater than 1,000 cfu at background);
A 2% chance that exposure to airborne Aspergillus fumigatus spores will be more than 5,000 cfu (5 times higher than background level) and 17% chance that exposure to airborne Aspergillus fumigatus spores will be more than 1,000 cfu (that is, a 17% chance of exposure being greater that highest background levels).

Other frequently asked questions (FAQs)

I work at a composting site. Will I be exposed to bioaerosols and will they affect my health?

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 (eg, 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 ie 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.

I live near a composting site. Will I be exposed to bioaerosols and will they affect my health?

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).

Are there any other health and safety issues associated with composting sites?

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