Indoor Air Quality

What is meant by indoor air quality?

According to the US Environmental Protection Agency, indoor air is often more seriously polluted than outdoor air. Given that many of us spend up to 90 per cent of our time indoors or in vehicles this is significant. For general health, well-being and safety reasons, human beings require a comfortable indoor temperature with air free from dust, irritants, pathogens, unpleasant odours, mould and mildew and other contaminants. Many factors affect indoor air quality (IAQ) in hotels and office buildings including:

  • levels of outdoor pollution, caused for example by smog, traffic or aircraft emissions and pesticides
  • sources of indoor pollution including the materials used in the fabric of buildings, carpets and soft furnishings, smoking, cleaning chemicals and the use of perfumes and salon products (see table 1)
  • the rate of exchange between indoor and outdoor air, i.e. ventilation rates and distribution
  • the amount of moisture in the indoor environment, which is considerably increased in hot humid climates, near kitchen areas and if the hotel has a gym, spa or indoor swimming pool. In serious cases this can lead to the growth of mould and mildew which has health implications

Table 1: Common indoor air pollutants

Pollutant Sources Health effects
Ammonia Cleaning products Irritates eye and mucous membranes
Bacteria Legionella, moulds and fungi and mildew Potentially fatal in the case of Legionnaires Disease. General worsening of respiratory complaints
Carbon dioxide (CO2) Respiration, combustion Feelings of stuffiness, drowsiness
Dust and particles Carpets, surfaces, smoking A range of allergic symptoms depending on size and nature of particles
Formaldehyde Foam insulation, fabrics, furniture, fire retardants, adhesives, carpet backing, cigarette smoke Can irritate eyes, skin and mucous membranes and cause headaches and asthma
Carbon monoxide (CO) and nitrogen dioxide (NO2) Leaking combustion devices (boilers, cookers) Worsening of respiratory complaints
Odours Cooking, smoking, perfume etc. Annoyance, stress and allergic reactions
Viruses, infectious diseases Humans and animals, e.g. SARS and Bird Flu Wide-ranging
Volatile Organic Compounds (VOCs) Solvents, aerosol sprays, cosmetics dry-cleaning, paints, pesticides, smoking Wide-ranging – including eye, skin and mucous membrane irritation

Why is IAQ important?

IAQ is of great importance in the hotel environment for the following reasons – many of them with potentially significant financial implications:
It is your legal responsibility to ensure the safety of staff, guests and customers at all times. This includes, for example, the safe functioning, adequate ventilation and proper maintenance of boilers and heating systems to avoid creating toxic fumes such as carbon monoxide. In October 2006 two children died from carbon monoxide poisoning due to fumes from a defective gas appliance at their hotel bungalow in Corfu.

You are also obliged to ensure you do not create a risk to public health through for example:

  • Legionnaires disease – this is a rare form of pneumonia that can be contracted through the inhalation of droplets of contaminated water transmitted in the form of spray. The risks are associated with poor maintenance of air-conditioning systems, showering facilities, whirlpool and spa baths and fountains. Legionella bacteria are unlikely to be detected by staff or guests until someone falls seriously ill. Not only are companies that are found responsible for incubating Legionnaires disease liable to prosecution and fines, it is potentially fatal (killing around 4,000 people around the world each year) and could expose you to compensation claims.
  • Certain moulds such as the toxic Stachybotrus chartarum thrive in damp and humid conditions. They can cause hay-fever like symptoms and affect sufferers of chronic lung diseases such as asthma. People with lower immunity are also at risk of infection from moulds.
  • Allergies can be exacerbated by air-conditioning, dust mites or materials to which they are allergic in guest bedrooms.

Guest satisfaction – often guests will not complain about a stuffy environment or a room that exacerbates any allergies they may have, but they are unlikely to return or recommend your hotel to others.
Staff productivity – staff cannot work efficiently and effectively if they are uncomfortable. This will affect their concentration, productivity and how they relate to your clients. Poor air quality can cause headaches, tiredness, dry or sore eyes or throat, skin irritation, dizziness and even nausea. So-called ‘sick building syndrome’ can have a detrimental effect on long-term health.

Reduced operating costs by reducing energy consumption (and your carbon dioxide emissions) through investment in modern, efficient air-conditioning equipment and proper maintenance.

Case Study: Sandic
Scandic has more than 11,500 ‘eco-rooms’ which are popular with guests because of their Nordic, natural aesthetics and the better indoor air quality they provide for allergy sufferers. The company renovates around 2,000 rooms each year, all of which are carried out according to the Scandic Environmental Refurbishment Equipment and Construction Standard (SERECS) which was introduced in 2001. All floors are made of sustainably-sourced wood, as is the furniture, and textiles used are wool or cotton, with as few fittings as possible made of chrome, rare metals or plastic.

Chilled beam technology is used to create a comfortable in-room climate, and climate control (as well as all other energy use in the hotels) is on a highly energy-efficient ‘on-demand’ basis. Jan Peter Bergkvist, Director of Environmental Sustainability for Hilton International Operations and Scandic stresses that focused maintenance of all air handling units and changing filters is a crucial, and often forgotten, part of improving in-room quality. “We also use central vacuum cleaners to improve air quality and at Scandic we do not use air-humidifiers in order to avoid the risk of bacteria building up. The new downtown Scandic Anglais in Stockholm, Sweden is our first hotel where we are using non-chemical, steam cleaning of guest rooms to further improve air quality and to minimise the spread of man-made substances” he says.

How can it be improved?

Your country should have target levels and maximum allowed concentrations for common contaminants as well as recommendations for indoor climate classification systems. It is also worth referring to the resources listed here.

Building design, extension and refurbishment

  • Radon is a colorless, odorless, radioactive gas, the most common indoor source of which is uranium in the local soil or rock. As uranium breaks down naturally, it releases radon gas which enters buildings through cracks in concrete walls and floors, floor drains, and sumps. The concern when concentrations build up indoors is that it can increase the incidence of lung cancer, particularly in smokers. Where it is known that soil radon concentrations are high, radon protection measures should be taken. In England and Wales this is covered by building regulations.
  • A hot, humid climate is more likely to cause indoor air quality problems than a hot dry one. Various design techniques can be employed in buildings to avoid or reduce the need for air-conditioning. These include designing the building envelope to take solar loads into account, and the use of natural cross-ventilation whereby windows are located on both sides of the room, helping to create airflow across the space.
  • For buildings without air-conditioning, the use of high ceilings, ceiling fans and louvred shutters will all help the flow of air and keep the temperature comfortable for occupants.
  • Fresh air intakes for ventilation systems should be located away from pollution sources such as main roads or cooling towers in order to avoid the danger of contamination by traffic fumes or legionella respectively.
  • In new or refurbished establishments, proper commissioning should be undertaken to balance all ventilation and AC systems before commencing operation.
  • Until the 1970s, asbestos was commonly used in many types of building products and insulation materials. It can still be found in old steam pipes, boilers and ducts, floor tiles, decorative material and textured paints sprayed on walls and ceilings. Loose, crumbly, or water-damaged material may release microscopic fibres which, if inhaled, can damage the lungs. Do not dust, sweep, or vacuum debris that may contain asbestos and avoid sanding, drilling or scraping such material. It is important to seek help from a qualified professional to handle and dispose of it. Some countries, such as the UK, require building facilities managers to have an asbestos management programme in place.
  • Ensure adequate ventilation in underground car parks. Fans should be fitted with sensors so that they can automatically regulate air quality. This will result in considerable savings over having fans running on a 24-hour basis.
  • Use natural, sustainably-produced materials (such as wood) wherever possible for interior design.
  • Avoid the use of plywood and other materials that contain formaldehyde. In some countries it is still used in the manufacture of wooden furniture items.
  • Make sure all paints, varnishes and adhesives used in building and refurbishment are free of solvents, or contain negligible amounts. Manufacturers should be able to provide independent scientific information as to whether their products meet stringent criteria for emissions, which you should consult before purchasing.
  • New carpets can contain chemicals that may irritate skin and eyes. Ask your supplier for information on what the carpet contains and whether it will cause emissions before purchasing. If possible, unroll and air the carpet in a well-ventilated area before installation and leave rooms to air for at least 24 hours after fitting.

Air-conditioning and ventilation systems

Fresh air quantities and flow

  • ‘Tight’ buildings where outdoor air intake is controlled mechanically and well-filtered before being distributed around the building can provide very high quality indoor air, especially if high-efficiency filters are used.
  • Minimum fresh air flow rates are defined according to national building codes. A typical value is 8-12 litres of fresh air per second (l/s) per person.
  • Fresh air quantities can be greatly increased when energy recovery from exhaust air is used to pre-heat or pre-cool fresh air. Heat recovery devices, such as air-to air heat exchangers, can recover 75% of the waste heat in exhaust air.
  • Carbon dioxide (CO2) levels are an indication of the number of people and the air quality in a room. Indoor levels should not exceed 1,000 ppm (parts per million). Automatic CO2 control improves the ability of air-conditioning systems to adapt to variable indoor ambient parameters.
  • Poor extraction over cooking appliances can lead to spillage of pollutants into the kitchen and restaurant areas. Choose a supply and extract combination that directs contaminants towards the extract in the most efficient way. Vapour and fine particulate grease can effectively be removed from exhaust systems using Ultra Violet (UV) light treatment.
  • Ensure that vents are not blocked by furniture or other obstructions.


  • Regular maintenance and cleaning of your Heating, Ventilation and Air-Conditioning (HVAC) equipment is essential to ensure it is filtering and circulating air correctly and that there are no air leaks or blockages.
  • It is important that proper pressurisation is maintained in order to avoid pollutants entering the hotel.
  • In humid climates, cooling coils must be steam-cleaned regularly to remove any build-up of deposits and bacteria.
  • Clean and replace high-efficiency filters regularly (twice a year minimum). Vacuum clean heat exchangers and front panels of chilled beam systems once a year.
  • Make sure no rainwater is leaking into the building and into the AC system – this can lead to microbial contamination (including legionella) and the disbursement of spores throughout the building.
  • Monitor water quality in cooling towers and condensation drains regularly.
  • If you have a dry-cleaning operation in the hotel, ensure that the extraction system is sufficient to cope and that it is not allowing solvent spillage into the hotel air.


  • Ensure that you purchase equipment that uses refrigerant that conforms with the requirements of the Montreal Protocol3, the international agreement covering the use and phasing out of Ozone Depleting Substances (ODS). Currently, the most environmentally responsible choice is systems using natural refrigerants.

As a general guide:-

  • Chlorofluorocarbons (CFCs) and Hydrochlorofluorocarbons (HCFCs) are ozone-depleting Hydrofluorocarbons (HFCs) are non ozone-depleting (zero ODP), but have significant global warming potential (GWP)
  • Natural refrigerants: Ammonia has zero ODP and zero GWP, and hydrocarbons (HCs) – i.e. propane and butane – have zero ODP and negligible GWP.
  • Never substitute alternatives without first checking with your equipment supplier that they are compatible with your system. In some cases, modifications may be necessary before using replacements or it may be necessary to replace the equipment altogether.

Cleaning and standards of hygiene

  • In order to minimise the risks of Legionnaire’s disease:
    • hot water should be stored above 60ºC (thermostatic mixing valves should be installed on showers and taps to prevent scalding).
    • shower-heads and spa jets should be regularly cleaned and flushed through. Ozone treatment along with other, newer purification technologies is environmentally preferable to chlorine, but if this is not possible use a 5-10mg/litre chlorine solution.
    • care should be taken in the choice of materials in contact with warm water to ensure they do not serve as nutrients for the legionella bacteria.
  • Dust and vacuum all soft furnishings daily. In hotel bedrooms, this should be done as early as possible during the day so that any dust can settle before the room is occupied for the night.
  • Carpets are often blamed for poor air quality, either for emissions or for dust mites and airborne debris. However, they can help to hold the allergens out of the air until it is vacuumed, so the key issue is to ensure regular maintenance and cleaning. Concentrate on the areas which get the most use – such as the hotel entrance, corridors, passageways into and out of rooms, stairways and elevators and eating areas. Deep clean carpets regularly to avoid the abrasion of embedded dirt.
  • Purchase commercial floor cleaning equipment that has strong suction and enclosed bags with good filtration. This will ensure that the dust particles are not circulated back into the air into furnishings and beds.
  • Volatile Organic Compounds (VOCs) can accumulate in the indoor environment and cause symptoms such as tiredness and discomfort in the eyes, throat and skin. Concentrations of as little as 0.2 milligrams per cubic metre of air can cause discomfort to allergy sufferers.
  • Solvents used in inks, paints, glues, rubber cement, felt- tip pens and white-out fluids all contribute and can build up if there is insufficient fresh air in the room. Review your use of office products and paints and avoid the use of solvents wherever possible. If solvent use is essential, ensure that lids are replaced on containers (even during use) as this will cut down on vapour loss.
  • Review your cleaning and laundry operations and identify where you can replace chemicals with environmentally preferable alternatives.

Case Study: JW Marriott Hong Kong
Many people know of tea tree oil as an essential oil for massage and body treatments in spas. It was also widely used during the first World War to treat wound before the advent of penicillin.

Because of the oil’s ability to kill bacteria, the JW Marriott Hong Kong adds it on a quarterly basis to the fresh air supply system where it is particularly effective in stopping mould growth. The hotel did not want to use a fixed atomising system as it required carbon dioxide to atomise and mist the oil into the air system, so it is atomised manually instead.

The use of tea tree oil has reduced the incidence of mildew in the air and corners in the rooms, particularly during summer periods when the average humidity reaches 85 per cent. The air-conditioning ducts and fan coil units are also cleaner than they were found to be in the past. The practice has been carried out throughout the hotel since 2000 and there are now seldom guest complaints about mould and mildew. In order to have total confidence, the hotel took air samples and tested them for mould with a self-test laboratory kit in 2003. All the results, except for one sample from the garbage room, were negative. In 2004 the hotel employed an IAQ analysis company to test its air quality. Hundreds of air samples were taken at various points throughout the hotel and apart from on the floors permitting smoking, the results were very good. The hotel is reducing smoking floors year by year and currently it is permitted in only 11 per cent of rooms.

Although tea tree oil has not been laboratory proven to kill the bacteria that cause Severe Acute Respiratory Syndrome (SARS), the hotel applied it to the fresh air system each month during the outbreak in Hong Kong as a precautionary measure.

Case Study: J W Marriott Mumbai, India
In November 2005 the JW Marriott Mumbai hosted India’s first indoor air quality conference with the help of the National Air Duct Cleaners Association (NADCA). They looked at issues such as proper duct cleaning and coil treatment using enzyme-based bio-active chemicals.

As a result of the conference the hotel decided to start an awareness-raising campaign as to the importance of IAQ, both in new building design and in the renovation of existing facilities. The hotel is now focussing attention on the four key elements of ventilation, filtration, pressurisation and maintenance of HVAC systems. Dust removed from the ducts resulted in an increase in air flow velocities through the air-handling units (AHUs) of between four and 69 per cent and a decrease in the pressure drop over the coil. This maximises air change through the heat exchanger and improves heat transfer. The biggest benefit of a planned duct maintenance programme according to Sunil Relia, Director of Engineering is that “it prevents the growth of fungi, mould and other microbiological organisms so we get clean and healthy air to breathe”.

Table 2 – Air purifying plants

Latin name Common name(s)
Philodendron Heartleaf or Elephant Ear varieties
Dracaena Cornstalk, Janet Craig or Warneck varieties
Hedera helix English Ivy
Chlorophytum comosum Spider Plant
Ficus benjamina Weeping Fig
Epipiremnum aureum Golden Pothos
Spathiphyllum `Mauna Loa' Peace Lily
Aglaonema modestum Chinese Evergreen
Chamaedorea sefritzii Bamboo or Reed Palm
Sansevieria trifasciata Snake Plant

Source: Clean Air Gardening

Resources and Further Reading

ASHRAE Standard 62-1999, Ventilation For Acceptable Indoor Air Quality

Building Air Quality: A Guide for Building Owners and Facility Managers

Clean Air Gardening

Improved Productivity and Health from Better Indoor Environments

Indoor Air Quality

The Building Air Quality (BAQ) Action Plan

The Inside Story: A Guide to Indoor Air Quality

WHO air quality guidelines – Second edition

More information

American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE)

Building Owners and Managers Association International

Building Research Establishment


Chartered Institute of Environmental Health (CIEH)

Multilateral Fund for the Implementation of the Montreal Protocol

National Institute for Occupational Safety and Health (NIOSH)

UNEP Division of Technology, Industry and Economics (DTIE) Energy and OzonAction Unit

US Environmental Protection Agency (USEPA)

World Green Building Council

World Health Organisation

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