Education And Debate


BMJ 1996; 313 doi: (Published 14 September 1996) Cite this as: BMJ 1996;313:674
  1. P H Appleby
  1. Paul Appleby is divisional director of Building Health and Safety, a division of Thorburn Colquhoun, London.

    The idea that buildings can make people ill is one that undermines deep seated beliefs in the function of buildings. Buildings are supposed to provide shelter and a safe environment where people are protected from the elements. The idea of illness associated with manufacturing or mineral extraction is reasonably well understood. However, people becoming ill because of exposure to some unseen agent in their home, school, or office can create a panic out of proportion to the risk.

    Building related illnesses fall into two categories: those that have an identifiable cause—such as legionellosis, humidifier fever, and conditions resulting from exposure to known substances such as asbestos, lead in paint, formaldehyde, etc—and those that have no readily identifiable cause but can be described only by a group of symptoms known as sick building syndrome.


    Algal growth on drift eliminators of a building's cooling tower—a potential source of pollutants.

    Sick building syndrome

    The term sick building syndrome is used to describe a situation in a building where more people than normal suffer from various symptoms or feel unwell for no apparent reason. The symptoms tend to increase in severity with the time that people spend in the building and to steadily improve or disappear when people are away from the building.


    The symptoms associated with sick building syndrome are those associated with common illnesses and allergies, usually in a relatively mild form so that many sufferers may not see a doctor and may not take time off work.

    Symptoms associated with sick building syndrome

    • Eyes—irritated, itching, dry, watering

    • Nose—irritated, itching, runny, dry, blocked

    • Throat—sore, constricted, dry mouth

    • Head—headache, lethargy, irritability, difficulty in concentrating

    • Skin—dryness, itching, irritation, rashes


    There is no single known cause of sick building syndrome, but there are several risk factors that have been identified from a large number of studies on the epidemiology of the syndrome and investigations of “sick” buildings.

    It is evident that some of these factors may combine to cause particular symptoms. For example, eye symptoms may be caused by a combination of long term use of a display screen, low humidity, airborne dust, and irritating airborne solvents.

    The increase in use of computers seems to have been a major contributing factor to the onset of sick building syndrome. The additional heat load has led to either overheating or the installation of air conditioning, while the nature of working at a display screen has not only created eye problems but also headaches and musculoskeletal symptoms.

    Risk factors for sick building syndrome

    Characteristics of work and building

    • Sedentary occupation, clerical work

    • More than half of occupants using display screen equipment for more than 5 hours a day

    • Maintenance problems identified

    • Low ceilings—typically lower than 2.4 m

    • Many changes or movements of furniture and equipment

    • Public sector tenant or occupant

    • Large areas of open shelving and exposed paper

    • Sealed building and city centre location

    • Large size—typically an occupied floor area greater than 2000 m2

    • Centralised control of environmental conditions—no local control of heating, ventilation, etc

    • Building more than 15 years old

    • Scruffy appearance

    • Large areas of soft furnishings, carpets, and fabrics

    Environmental factors

    • Low room humidities

    • Low supply rate of outdoor air

    • Smoking permitted in work areas

    • Damp areas and mould growth

    • Dust, solvents, and ozone emissions from printers and photocopiers

    • Low frequency fluorescent lamps creating subliminal flicker

    • High room temperatures

    • Excessive supply rate of outdoor air

    • Dusty atmosphere

    • Gaseous emissions (volatile organic compounds) from building materials and cleaning products

    • Low frequency noise

    Criteria covered by Health and Safety (Display Screen Equipment)

    Regulations 1992

    • Daily work routine of users

    • Eye tests

    • Provision for training and information

    • Risk assessment and analysis of workstations

    • Requirements for workstations

      Display screen Keyboard

      Work desk Work chair

      Task design Software

      Environment—heat and noise

    Concern about display screens resulted in a European Commission directive. In Britain this was enacted under the Health and Safety (Display Screen Equipment) Regulations 1992, which requires all users to be trained and provided with certain facilities. From January 1997 all workstations which include a display screen will have to meet the criteria.

    Types of building affected

    Sick building syndrome not only occurs among office workers. It has been identified in schools, nurseries, libraries, and apartment buildings.

    Investigating sick building syndrome

    An “outbreak” of sick building syndrome may not be obvious. It may come to light because of complaints to personnel, building maintenance, or occupational health departments rather than to general practitioners.

    The Health and Safety Executive have produced the pamphlet How to deal with sick building syndrome—Guidance for employers, building owners and building managers. This gives a useful guide to the steps that should be taken before calling in a professional investigator.

    Steps in investigating a suspected outbreak of sick building syndrome

    • Check for local flu or cold epidemic

    • Check for breakdown of air conditioning or ventilation system

    • Check for major pollution sources, both indoors and outdoors

    If there is nothing obvious then

    • Check with staff for nature and extent of symptoms and complaints

    • Check absenteeism records

    • Check maintenance history

    If action on the above does not alleviate the problem then

    • Review design, operation, control, and maintenance of heating, ventilation, and air conditioning and check against original design specifications

    • Check whether changes in layout of partitions and space and use of building have interfered with operation of heating, ventilation, and air conditioning

    • Check organisation of work and management practices

    If necessary specialist advice should be sought on further investigations

    • The Royal Society of Health has designed a questionnaire for this purpose, published by the Building Research Establishment.

    Problems with indoor air

    Concentrations of pollutants in non-industrial buildings are generally orders of magnitude below published limits for occupational exposure. Air quality is rarely a problem in the absence of other factors that contribute to the symptoms which make up sick building syndrome. Exceptions can occur, however, when there are unusual sources of pollution or inadequate ventilation.

    Larger dust particles in outdoor air should be removed by filters in a building's central air handling plant, which supplies treated air to the building. If these filters are neglected, however, they can become overloaded or disintegrate and provide a source of pollution. If the filters are ineffective, dust will coat the inside of the heating and cooling coils, fans, silencers, and duct work. Where moisture is present, such as in cooling coils that take moisture out of the air, a sludge can form and growth of mould is possible. Dirty air handling systems can also generate odours, which are distributed throughout the building.

    Common indoor air pollutants and their sources

    Tobacco smoke


    Source: Photocopiers and printers

    Volatile organic compounds

    Source: Carpets, furniture, building materials, paints, cleaning agents


    Source: Outdoor air, skin, paper, printer and photocopy toner, mineral and glass fibre

    Carbon monoxide

    Source: Traffic, combustion (such as gas cookers), tobacco smoking

    Oxides of nitrogen

    Source: Traffic, combustion (such as gas cookers)

    Isocyanates—Toluene, diphenylmethane, hexamethylene, naphthalene

    Typical indoor concentration: 50-103 μg/m3 (trace outdoors)

    Possible sources: Adhesives, sealants, environmental tobacco smoke, wall and floor coverings, paint, moth crystals (naphthalene)


    Typical indoor concentration: 0-0.6 ppm (0-0.03 ppm outdoors)

    Possible sources: Urea formaldehyde foam insulation, fabrics, carpets, environmental tobacco smoke, floor and wall coverings, adhesives, sealants, lacquer, plywood, chipboard, gypsum board, disinfectants


    Most airborne allergens (aeroallergens) are organic particles with a mean mass aerodynamic diameter of less than 10 μm. Some are aerosols or vapours.

    An allergen's size dictates where it lodges in the airways: smaller particles penetrate the alveoli and cause alveolitis, those of 5-30 μm size tend to lodge in the bronchi and may induce bronchospasm, while larger particles lodge in the nose and give sensitised people rhinitis. Particles that lodge in the eyes may cause conjunctivitis. Allergens of small size, such as some chemicals, may combine with human proteins to cause allergic reactions.

    The concentration of allergens in most homes is usually much higher than in offices, particularly in older houses with gardens and pets. House dust mites thrive in mattresses, while moulds grow in gardens, bathrooms, etc.

    Airborne allergens in the workplace

    House dust mite excreta

    Typical indoor concentration: 0-60 mites/g dust

    Possible sources: Carpets, upholstery

    Fungal spores—Penicillium, Cladosporium, Aspergillus, Alternaria,

    Trichoderma, Stemphylium, Mucor

    Typical indoor concentration: 10-103 spores/m3 (104 spores/m3 outdoors)

    Possible sources: Damp surfaces

    Di-isocyanates—Hexamethylene di-isocyanate (HDI), toluylene di-isocyanate

    (TDI), 4:4'-di-isocyanate-diphenyl methane (MDI)

    Possible sources: Urethane foams

    Phthalate anhydrides

    Possible sources: Epoxy resins

    Natural resins

    Possible sources: Timber


    Possible sources: Biological detergents

    Insect detritus

    Animal proteins

    Exposure to chemicals may be greater in newly decorated and furnished offices, although formaldehyde has been largely phased out by furniture and fabric manufacturers in Britain. The forced movement of air in air conditioned and ventilated buildings may encourage circulation of mould spores and other allergens, especially if they are present within the air handling system itself. Some poorly maintained air handling systems may experience mould growth in filters and humidifiers, although excessive growth is rare.

    Action plan to improve air quality in buildings

    • Use materials with components of low volatility and low toxicity

    • Allow new carpets and soft furnishings to lose most of their volatile component before occupation by workforce

    • Minimise use of fibrous materials for finishes and maximise use of wipeable surfaces

    • Provide enclosed storage for files, books, and papers

    • Ensure there is no penetration by rain or condensation problems

    • Ensure that plaster, concrete, etc, has dried out thoroughly before occupation

    • Use photocopiers and laser printers with integral devices to reduce ozone production

    • Consider banning smoking in work areas

    • Isolate dirty and malodorous processes and areas from working or living areas and keep them under negative pressure

    • Locate air inlets away from roads and other sources of pollution

    • Fit air conditioning and ventilation supplies with high efficiency filters

    • Do not allow filters to become too dirty or dirty air to bypass them

    • Keep inside of air handling system clean

    Humidifier fever

    Actinomycetes are filamentous bacteria which resemble fungi in form and in the types of disease they produce. Thermophilic actinomycetes have been implicated in outbreaks of extrinsic allergic alveolitis such as farmer's lung and mushroom worker's lung, as well as the form of allergic alveolitis called humidifier fever.

    A spray humidifier consists of a network of pipes mounted across the airstream. The pipes contain spray nozzles and are connected to a pump which draws water from a tank or pond beneath and through which water is recirculated.

    Outbreaks of humidifier fever are rare but generally dramatic when associated with heavily contaminated spray humidifiers or air washers. Occasionally, spray humidifiers have been used to wash out particulates from the air in place of filters. This creates a large volume of sludge which forms in the pond and on downwind surfaces. This sludge can provide the nutrients for microbiological growth.


    Internal view of spray humidifier in air supply to a building.


    Legionellosis is a generic term which describes Legionnaires' disease and Pontiac fever. These are relatively uncommon infections, with about 200 cases reported annually in England and Wales, although the reporting rate is thought to be only 10% because the symptoms can be mistaken for other types of pneumonia. These diseases are caused by inhalation of water droplets or particles containing motile thermophilic bacteria of the family Legionellaceae, of which there are some 40 species. The one most commonly associated with Legionnaires' disease is Legionella pneumophila serogroup 1, there being 14 serogroups. L pneumophila has also been implicated in flu-like illnesses which have been named after the places where they were first reported—that is, Pontiac fever and Lochgoilhead fever.


    Small, rod shaped bacteria of Legionella pneumophila in culture from lung tissue.

    These bacteria are small and rod shaped and penetrate deep into the alveoli, where they cause infection. There is an incubation period of two to 10 days before the symptoms appear, and it is thought that only 1% of those exposed develop symptoms. The symptoms of Pontiac fever may develop after only five hours or up to three days after exposure.

    Although legionella bacteria are found in nature, they tend not to become a problem unless they enter building water systems, which create an aerosol that can be inhaled by susceptible people and which provide a suitable niche for the multiplication of the bacteria

    In its most severe form Legionnaires' disease is a pneumonia that can be fatal or leave the patient debilitated if it is not treated in time. Initial symptoms include high fever, chills, headache, and muscle pain. A dry cough soon develops, and most patients experience difficulty with breathing. Patients may also develop diarrhoea and vomiting and become confused and delirious.

    Systems and equipment which can be a source of legionellosis

    • Evaporative cooling towers and condensers

    • Spray humidifiers and nebulisers

    • Hot and cold water systems serving taps and showers

    • Spa baths and whirlpools

    • Horticultural misting systems

    • Car washes and lances

    • Lathe coolant systems


    Where there is a risk of legionellosis steps should be taken to ensure that equipment and systems are kept as clean as possible and regularly disinfected. If possible, water temperatures should be kept either below 20°C or above 50°C. If this is not possible biocides should be added to the water to prevent legionella bacteria multiplying, provided the biocides cannot enter the indoor air; thus, ongoing treatment of water is not possible with hot and cold water systems or spray humidifiers.

    Risk factors in outbreaks of legionellosis

    • Water temperature between 20°C and 50°C

    • Nutrients available for growth, such as proteins and rust

    • Niches which will protect Legionella from heat and biocides, such as limescale and sludge

    • Fine (invisible) aerosol such as that generated from taps, shower heads, cooling towers, and spray humidifiers

    • Low water turnover—temperature may rise, biocides decay, and sediment precipitate to form a sludge

    • Open to ingress of animals, insects, dirt, and sun—direct sunlight encourages algal growth

    • Susceptible people exposed to aerosol—for example, those with impaired lung capacity or immune system

    Guidance on the design and maintenance of these systems is given in the Health and Safety Executive's guidance note The prevention and control of legionellosis.

    Recommended further reading

    • Health and Safety Executive. How to deal with SBS—Guidance for employers, building owners and building managers. London: HMSO, 1995.

    • Chartered Institution of Building Services Engineers. Healthy workplaces. Balham: CIBSE, 1993. (CIBSE GN2:1993.)

    • Health and Safety Executive. Display screen equipment work. London: HMSO, 1992.

    • Health and Safety Executive. The prevention and control of legionellosis. London: HMSO, 1991. (HS(G)70:1993.)

    The ABC of Work Related Disorders is edited by David Snashall, clinical director of Occupational Health Services, Guy's and St Thomas's Hospitals NHS Trust, London.

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