World Health Organization
Development of WHO Guidelines for Indoor Air Quality: Dampness and Mold
Report of a Working Group on Mold (published 2008)
This very significant document provides an overview of the known risks from mold exposure, and what should be done about them (recommendations). As a primarily European workgroup, it is interesting to note the difference in what the U.S. Centers for Disease Control is telling us about mold and health and what this workgroup from the esteemed World Health Organization found to be true. At The Center for School Mold Help, we find this document as an accurate beginning in describing the problem of mold on health, as experienced in damp buildings - and in the case of the United States, this describes most schools (SMH).
Microbial pollution is one of the key constituents of indoor air pollution. It consists of hundredsof species of bacteria and fungi, and in particular filamentous fungi (moulds) growing indoorswhen sufficient moisture is available. Health problems associated with moisture and biologicalagents include increased prevalence of respiratory symptoms, allergies, and asthma as well asperturbation of the immunological system. Based on the extensive review of the scientificevidence, this WHO working group identified the main health risks due to excess moisture,associated with microbial growth and contamination of indoor spaces. It also formulated WHO guidelines for protecting public health, recommending that persistent dampness and microbial growth on interior surfaces and in building structures should be prevented (or minimized) as they may lead to adverse health effects.
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Development of WHO Guidelines for Indoor Air Quality: Dampness and Mold
Summary of the health risk evaluation
1. Sufficient epidemiological evidence from studies conducted in different countries and climatic conditions shows that occupants of damp or mouldy buildings, both homes and public buildings, are at increased risk of experiencing respiratory symptoms, respiratory infections and exacerbations of asthma. Some evidence suggests an increased risk of developing allergic rhinitis and asthma. Although not many intervention studies are available, their results show that remediation of dampness problems leads to a reduction in adverse health outcomes.
2. There is clinical evidence that exposures to moulds and other dampness-related microbial agents increase the risk of rare conditions, such as hypersensitivity pneumonitis/allergic alveolitis, chronic rhinosinusitis and allergic fungal sinusitis.
3. Toxicological evidence in vivo and in vitro supports these findings by showing diverse inflammatory and toxic responses after exposure to specific microorganisms isolated from damp buildings, including their spores, metabolites and components.
4. While groups such as atopic and allergic individuals are particularly susceptible to exposures to biological and chemical agents in damp indoor environments, adverse health effects have also been widely demonstrated in non-atopic populations.
5. The increased prevalence of asthma and allergies in many countries increases the number of people susceptible to the effects of dampness and mould in buildings.
6. The prevalence of indoor dampness ranges widely within and among countries, continents and climate zones. It is estimated to be in the order of 10–50% of the indoor environments in Europe and North America, as well as in Australia, India and Japan. In some specific settings, such as river valleys or coastal areas, conditions of dampness are substantially higher than national averages.
7. The amount of water available on/in materials is the most important factor triggering the growth of microorganisms, including fungi, actinomycetes and other bacteria.
8. Microorganisms in general are ubiquitous in all general environments. Microbes propagate rapidly whenever water is available. The dust and dirt normally present in most indoor spaces provide sufficient nutrients to support extensive microbial growth. While mould growth is possible on all materials, appropriate material selection is nevertheless important to prevent dirt accumulation, moisture penetration and mould growth.
9. Microbial growth may result in elevated levels of spores, cell fragments, allergens,
mycotoxins, endotoxins, ß-glucans, and microbial volatile organic compounds (MVOCs) in indoor air. The causative agents of adverse health effects have not been conclusively identified, but excessive levels of any of these in the indoor environment indicates a potential health hazard.
10. Microbial interactions and moisture-related physical and chemical emissions from building materials may also play a role in dampness-related health issues.
11. Building standards and regulations on comfort and health do not sufficiently emphasize requirements to prevent and control excess moisture and dampness.
12. Besides occasional events – such as water leaks, excess rain, floods, etc. – most moisture enters buildings through incoming air, including that infiltrating though the envelope, or is due to occupants’ activities.
13. Allowing surfaces to become cooler than the surrounding air may result in unwanted condensation. Thermal bridges (such as metal window frames), inadequate insulation and unplanned air pathways, or cold water plumbing and cool parts of air conditioning units can result in surface temperatures below the dew point of the air that contribute to dampness problems.
14. The problem of excess moisture and dampness can be tackled by controlling the quality of the building envelope regarding air infiltration, exfiltration, and pathways of water intrusion, by ensuring adequate thermal insulation and by avoiding condensation indoors through the control of moisture sources and of temperature, humidity and velocity of the air in the proximity of the surfaces.
1. Persistent dampness and microbial growth on interior surfaces and in building structures should be avoided or minimized, as they may lead to adverse health effects.
2. Indicators of dampness and microbial growth include the presence of condensation on surfaces or in structures, visible mould, perceived mould odour and a history of water damage, leakage or penetration. Thorough inspection and – if needed – appropriate measurements may be used to confirm indoor problems related to moisture and microbial growth.
3. Currently, the relationship between dampness, microbial exposure and health effects cannot be precisely quantified, so no quantitative health-based guideline values or thresholds can be recommended for acceptable levels of specific microorganism contamination. Instead, it is recommended that dampness and mould-related problems be prevented. When they occur, they should be remediated because of the increased risk of hazardous microbial and chemical exposures.
4. Well-designed, -constructed and -maintained building envelopes are critical to the prevention and control of excess moisture and microbial growth by avoiding thermal bridges and preventing intrusion by liquid or vapour-phase water. Management of moisture requires proper control of temperatures and ventilation to avoid high humidity, condensation on surfaces and excess moisture in materials. Ventilation should be distributed effectively in spaces, and stagnant air zones should be avoided.
5. Building owners are responsible for providing a healthful workplaces or living environments free of excessive moisture and mould problems by ensuring proper building construction and maintenance. Occupants are responsible for managing water use, heating, ventilation, appliances, etc. in a proper manner that does not lead to dampness and mould growth.
6. Local recommendations in different climatic regions should be updated to control dampness-mediated microbial growth in buildings and to ensure the achievement of desirable indoor air quality.Dampness and mould may be particularly prevalent in poorly maintained housing for low income people. Remediation of conditions related to adverse exposures should be given priority to prevent additional contributions to poor health in populations already living with an increased burden of disease.
The WHO produced a document in 2000 called The Right to Healthy Indoor Air , WHO Regional Office for Europe, worth reading and citing.