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Contents

Introduction 1

Legislation on Controlling Indoor Air Quality 2

Impact of Indoor Air Quality on Health 3

Sources of Indoor Air Pollution 4

Common Indoor Air Pollutants 7Carbon DioxideBiological ContaminantsRadonVolatile Organic CompoundsFormaldehydeEnvironmental Tobacco Smoke

Understanding Your Ventilation System 16Natural VentilationMechanical VentilationMaintenance of Mechanical Ventilation SystemsFresh Air Supply Rate for General Work Activities inAir-conditioned Workplaces

Setting Air Quality Standards 19

Tips on Improving Indoor Air Quality 20

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1

However, many new buildings are now being designed as closed systems, in order to be more energy

saving. Only a small portion of air in circulation is fresh air introduced from outside. It is precisely

because of this lack of natural ventilation, that the growing quantity and diversity of synthetic materi-

als and chemicals used in interior decoration is contributing to an increased level of indoor pollution.

People whose occupation requires them to stay indoors (in offices, godowns, schools, hospitals,

restaurants, shopping malls, cinemas, and homes under renovation) for extended periods, are thus

subject to increasing health hazards.

Introduction

Living and working in a busy metropolis like Hong Kong, we normally spend 80% to 90% of our time

indoors. To make our indoor environment more comfortable and less extreme than the outdoor

environment, we need to use air-conditioning. For example, we warm the indoor air during the cold

season, and cool the indoor air during the hot season.

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1. Labour DepartmentOccupational Safety and Health Ordinance (Cap 509)✦ The person responsible for a workplace must ensure:

1. that the workplace is adequately ventilated by fresh air; and2. that, as far as reasonably practicable, the air within the workplace is kept free of impurities

(including fumes, dust and disease causing bacteria).✦ If it is not practicable to comply with the above subsection, the person responsible for the

workplace must:1. take all reasonably practicable steps to protect employees from inhaling impurities and to

prevent accumulation of the impurities; and2. ensure that effective exhaust devices are installed and used.

Factories and Industrial Undertakings Ordinance (Cap 59)✦ In every notifiable workplace, effective and suitable provision shall be made for securing

and maintaining, by the circulation of fresh air, the adequate ventilation, and for renderingharmless all fumes, dust and other impurities that may be injurious to health generated in thecourse of any process or work.

✦ In connection with any process or work carried on, exhaust appliances shall be provided andmaintained as near as possible to the point of origin of the dust or fume or other impurity, so

as to prevent its entering the air of any workroom.

2. Buildings DepartmentBuildings Ordinance (Cap 123)✦ If there is no natural ventilation in the office, then there must be the provision of mechanical

ventilation facilities, which can provide fresh air to every part of the working area at the rate

of at least 5 cycles per hour.

3. Food and Environmental Hygiene DepartmentPublic Health and Municipal Services Ordinance (Cap 132)✦ Provision of ventilating systems in scheduled premises (including restaurants, dance halls,

theatres, cinemas, funeral parlours and factory canteens):1. No air intake for the ventilating system shall be sited in any place where waste or rubbish is

likely to accumulate;2. The ventilation system must be inspected annually by a registered specialised contractor.

The inspection should cover every damper, filter and dust collector;3. The rate of fresh air supply should be at least 13-17 cubic metres per hour per person.

4. Other Government DepartmentsSmoking (Public Health) (Amendment) Ordinance (Cap 371)✦ Smoking in certain areas is prohibited, and health warnings and other information should be

displayed on cigarette packs and tobacco advertisements.

Legislation on Controlling Indoor Air Quality

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Polluted indoor environments can lead to discomfort, such as headaches, eye irritation, breathing

difficulties, skin allergies, fatigue, vomiting, and a series of acute or chronic symptoms and diseases.

EyesDryness, irritating, stinging pain and redness

Symptoms and Diseases Related to Air Quality

Upper Respiratory Tract (nose and throat)Dryness, irritating, stinging pain, nasal congestion, running nose, sneezing and sore throat

LungsChest tightness, dry coughing, bronchitis

SkinRedness, dryness, general and localized itchiness

Possible Diseases:HypersensitivityHypersensitivity pneumonitis, humidifier fever, asthma, rhinitis, dermatitis, sick building syndrome

InfectionLegionellosis (Legionnaire's disease), Pontiac fever, tuberculosis, common cold, flu

GeneralHeadache, weakness, drowsiness/lethargy, lack of concentration, irritability, anxiety, nausea, dizziness

Impact of Indoor Air Quality on Health

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1. Chemical Pollution✦ Carbon dioxide exhaled by employees

✦ Harmful substances (such as formaldehyde) emitted from furniture, carpets etc.

✦ Indoor work, such as:

Use of chemicals (insecticides, antiseptics,cleaning agents, etc.)

Burning activities (smoking, cooking,laboratory work etc.)

Use of harmful materials duringrenovation (thinners, paints, adhesivesetc.)

Poorly maintained cooling water towers caneasily breed bacteria.

Sources of Indoor Air Pollution

2. Biological Contamination✦ Coughing and sneezing can spread

bacteria or viruses

✦ Water stains and soil for flowers

and plants, act as breeding grounds

and nurseries for bacteria, fungi

and viruses, as do poorly maintained

vent i la t ion sys tems , such as

humidifiers and cooling towers

3. Pollution by Radiation✦ Radon emission mainly from building materials made of granite

✦ Radioactive materials used in physics or medical laboratories

✦ Leakage of improperly stored radioactive waste

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4. Pollution from Outside✦ Major pollutants from power plants, transport

vehicles and industrial production include:

• Carbon monoxide, sulphur dioxide,nitrogen oxides, volatile organiccompounds, polycyclic aromatichydrocarbons and suspendedparticulates

✦ Natural pollutants include:

• Dust, sand, sea salt particles, pollen,spores and micro-organisms

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Indoor working environments can contain a variety of air pollutants. Air pollutants of major concern in

Hong Kong include:

1. Carbon dioxide

2. Biological contaminants from human beings, pets and plants

3. Radon from building materials

4. Volatile organic compounds emitted from consumer products

(such as cosmetics, insecticides and cleaning agents)

5. Formaldehyde emitted from pressed wood products

(such as furniture)

6. Environmental tobacco smoke

Common Indoor Air Pollutants

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1. Carbon Dioxide✦ Carbon dioxide exhaled by employees is a major pollutant. A high concentration of carbon

dioxide means there is insufficient fresh air.

✦ This is usually caused by:

• improper partitioning leading to poorventilation

• over-congestion of working area

• inability to open windows

• poor maintenance or improper use ofventilation system resulting in low airreplacement rate

• inadequate supply of fresh air

The concentration of indoorcarbon dioxide must be regularlymeasured to assess the adequacyof the ventilation.

A high concentration of carbon dioxide means the supplyof fresh air is inadequate. This, combined with other airpollutants (such as body odours), makes the atmosphere stuffyand we may feel, drowsy or even sick.

Improvement Measures• If possible, open windows to increase ventilation;

if air-conditioners are used, maintain goodventilation with a sufficient supply of fresh air.

• Ensure that fresh air inlets are located well awayfrom sources of pollution.

• Avoid unnecessary partitioning of the premises.

• Avoid staying in congested indoor public areasfor extended periods.

• Improve the ventilation system, and increasethe rate of air replacement and the supply offresh air.

✦ If the concentration of carbon dioxide frequently exceeds 1,000 ppm, there is a need for the

inspection, maintenance, repair and improvement of the ventilation system.

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Fungi and bacteriacan grow in dirty air ductsand spread via air currents.

✦ Some biological contaminants trigger allergic reactions,

including hypersensitivity pneumonitis, allergic rhinitis,

and some types of asthma. Some fungi may also release

disease-causing toxins. Symptoms of health problems caused

by biological contaminants include sneezing, watery eyes,

coughing, shortness of breath, dizziness, lethargy, fever and

digestive problems.

Warm and humid places easily breedmicro-organisms.

2. Biological Contaminants✦ Biological contaminants include bacteria, fungi, viruses

and dust mites, all of which can trigger allergies.

✦ Bacteria easily spread through human, soil, plant and

animal residues.

✦ Dust mites are microscopic insects usually living in

humid and warm places such as carpets and woollen

materials.

Dirty carpets and furniture covers alsoact as breeding grounds for bacteria,fungi and fleas.

Bacteria Fungi

Very low <50 <2 <10 000

Low <100 <100 <20 000

Medium <500 <500 <50 000

High <2 000 <2 000 <120 000

Very high >2 000 >2 000 >120 000

Observed levels of micro-organisms in the airdust in non-industrial indoor environments

CFU*/m3 of air Fungi (CFU/g of dust)Category ofcontamination

Poorly maintained cooling towers can easilybreed bacteria.*CFU: colony-forming units

Source: Encyclopedia of Occupational Health and Safety,4th edition - International Labour Office, Geneva ✦ Poorly maintained ventilation systems can

be breeding grounds for fungi and other

biological contaminants.

✦ Biological contaminants grow faster when:

• there is insufficient ventilation

• it is warm and humid; or

• there is an accumulation of dust in thefilters and ducts of the air-conditioning orventilation system.

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Effective Measures for Reducing Biological Contamination• Keep the indoor environment clean. Regular cleaning helps to reduce dust mites and other sources

of allergies.

• Maintain good ventilation and try to keep the indoor air clean and dry. Eliminate sources of water orhumidity (such as leaking taps in the lavatory) which may cause the breeding of fungi. Keep theindoor relative humidity below 60%.

• Wherever possible, dismantle and dispose contaminated materials suchas mouldy ceilings tiles and carpets, or use a diluted bleaching agentto wash surfaces contaminated by fungi.

• Use efficient dust filters to reduce suspended particulates andspores of fungi from entering the ventilation system, and washthe dust filters regularly.

• Regularly inspect, maintain and clean the ventilation system,including the fan, dust filter, temperature control unit, ventilationducts and louvres, and implement effective antiseptic measures toprevent the breeding of biological contaminants.

Regular cleaning and sterilisation ofthe ventilation system can effectivelycontrol the growth of micro-organisms.

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3. Radon✦ Radon is a colourless, tasteless and

odourless radioactive gas.

✦ It is mainly emitted from soil, rock or

building materials such as concrete made

with granite. It can enter the basement,

ground-level floors or higher floors via

the walls, floors, or cracks on the ground.

✦ Poor ly vent i lated bui ld ings can

trap and accumulate radon.

✦ When radon is inhaled into the lungs, it

can accumulate and give off radiation.

People so affected run a higher risk of

lung cancer.

✦ For the same amount of radon inhaled,

a smoker is three times more likely to

have lung cancer than a non-smoker.

✦ The cement used in Hong Kong's construction

industry usually contains granite. Hence, it is likely

that the buildings have high concentrations of

radon. If its density exceeds the World Health

Organisation's reference values of 200 Bq per

cubic metre, measures should be taken to reduce

the level of radon.

Source: Encyclopedia of Occupational Health andSafety, 4th edition - International LabourOffice, Geneva

Radon is mainly emittedfrom building materialsmade of granite.

Fresh air will disperse radon inthe building.

Measures for Reducing Radon Exposure• Open your windows more often if your accommodation is naturally

ventilated.

• Set the fresh air intake and exhaust properly if you have airconditioners or ventilation systems.

• Fill in cracks on the floors or walls of basements or above-groundunits.

• Apply a less permeable wall covering such as wall paper.

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✦ Volatile Organic Compounds

(VOCs) are a diverse group

of organic compounds that

evaporate at room temperature.

✦ In a typical indoor environment,

there are more than 100 VOCs,

including formaldehyde, toluene,

chloroform, etc.

✦ Sources of these pollutants

include paint and thinners used

in decorating work, as well as

in wooden furniture, cosmetics,

cleaning agents, insecticides,

residual dry-cleaning agents on

clothing, tobacco smoke, etc.

✦ Exposure to VOCs may result in

both acute and chronic health

effects:

• Many types of VOC have adebilitating effect on thehuman central nervous system.

• Exposure to concentratedVOCs (such as unpacking newwooden furniture, or inhalingthe unpleasant smell whenusing a photocopier) cancause eye, nose and throatirritations, headaches, dizziness,visual disorders, and othersymptoms.

• S o m e V O C s ( s u c h a sfo rma ldehyde ) detec tedindoors are known human oranimal carcinogens.

Source: Encyclopedia on Occupational Health and Safety, 4th Edition –International Labour Office, Geneva

4. Volatile Organic Compounds

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New furniture, carpets, building materials, improper use ofinsecticides, and chemical gases produced during renovation,are all detrimental to the health of office staff.

How to Reduce VOC Pollution• Venti late indoor areas regularly and

thoroughly.

• When using paints, adhesives, cleaning agentsand other products containing VOCs indoors,the windows should be opened with theventilation system operates.

• Decoration and pest control work should takeplace during weekends or holidays, when thebuilding is less occupied. Upon completion ofwork, ventilate the affected area with freshair to dilute emissions.

• Wherever possible, products with a low VOCcontent should be used. The manufacturersshould be asked to provide information aboutthe levels of VOC emitted by their products.

• If employees' c lothing has just beendry-cleaned, make sure they are thoroughlydried before use. Source: Encyclopedia of Occupational Health and Safety,

4th edition - International Labour Office, Geneva

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On hot and humid days, the emissionof formaldehyde from wooden furniturewill be higher. Turning on the air-conditioner willlower the indoor temperature and humidity, andreduce the level of formaldehyde.

Reducing the Level of Formaldehyde in Workplaces• Avoid placing building materials, indoor decorations

or other formaldehyde emitting products (especiallylaminated-wood products made with urea-formaldehyderesins) inside the building.

• Choose laminate-finish pressed-wood products to reducethe possibility of formaldehyde emission from the woodenmaterials. Suitable formaldehyde barrier coatingmaterials include polyurethane varnish, oil-based alkyd resinpaint and thick vinyl film.

• New furniture should preferably be aired for at least several days or weeks before they are broughtindoors.

• Wherever possible, open windows as long as possible to reduce the accumulation of formaldehyde.

Source: Encyclopedia of Occupational Health and Safety,4th edition - International Labour Office, Geneva

Laminated-woodfurniture is one of themain sources of formaldehyde

✦ Concentrated formaldehyde can produce apungent odour and is highly irritating to theeyes and respiratory tract.

✦ Even brief contact can cause temporary burning or itching of eyes and nose, or a sore orburning throat.

✦ The American Conference of Governmental Industrial Hygienists (ACGIH) has classifiedformaldehyde as a suspected human carcinogen.

5. Formaldehyde✦ Indoor formaldehyde emissions mainly come from the furniture made of wood products with

adhesive or coating material. It is also produced by cigarette smoking as well as combustionsources (such as gas appliances, and kerosene heaters), and can also found in other interiorfurnishing-related items (such as foam insulation, adhesives, fabrics, carpets, etc.).

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6. Environmental Tobacco Smoke(ETS)✦ ETS is a mixture of the smoke given off by

the burning end of a cigarette, pipe, orcigar, and the smoke exhaled by thesmoker.

✦ More than 4,000 different gaseous andparticulate substances are emitted in ETS.Many of these are strong irritants and atleast 40 are known to cause cancer inhumans or animals.

✦ While smoking is hazardous to the healthof smokers, ETS also affects non-smokers

in the following ways:

• Irritation to the eyes, nose and throat;

• Increased risk of lung cancer and heartdisease;

• The respiratory system is easi lysusceptible to various infections,including coughing, wheezing, sputumproduction and impaired lung functions.

Not only is smoke unpleasant, it can also cause short-term andlong-term health problems, including eye irritations, cough,headaches, coronary and respiratory problems.

Protecting Yourself Against ETS• Strengthen estate management rules – allow

smoking only in independent rooms anddesignated smoking areas with independentventilation systems.

• Never allow smoke to spread into non-smokingareas.

• Advocate and implement a non-smoking policy.

Source: Encyclopedia of Occupational Health and Safety,4th edition - International Labour Office, Geneva

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1. Natural Ventilation✦ Natural ventilation (by opening the windows),

coupled with fans, will provide an adequate

supply of fresh air.

✦ The drawback of natural ventilation is

affected by the surrounding noise disturbance

and heat from outside during the summer.

✦ This is suitable only for controlling a low heat

load and very low emission of less toxic

contaminants.

✦ Premises relying entirely on natural ventilation

should have windows or other openings of

at least 5% to 10% of the floor area to obtain

adequate ventilation in the summer.

2. Mechanical Ventilation✦ Induced dilution ventilation

• Propeller fans extract contaminated air outof a building, thus lowering the air pressureinside the building and drawing fresh air fromoutside into the building through openings.

• Wherever possible, generate cross ventilation tolet sufficient fresh air into the building.

✦ Forced dilution ventilation

• The ventilation system usually consists of a fan, a cooling/heating unit and a ducting system.

• The system distributes filtered and temperature-conditioned air to the required locations inthe building.

Understanding Your Ventilation System

✦ Diluted ventilation PLUS natural ventilation are suitable for the control of heat load and

moderate emissions of gases and vapours of low toxicity.

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The cooling tower should be regularlycleaned and sterilised.

Wind-chilled cooling towers should beused instead of water-chilled coolingtowers.

Ventilation ducts should be regularlycleaned and sterilised.

The dust filters, fans and coolingcoils should be frequently washed.

High efficiency air filterss h o u l d b e u s e d a n dfrequently changed.

• Inspect and clean regularly all components of the ventilation system for cleanliness and avoidpossible growth of micro-organisms.

• The performance of the ventilation system should be regularly assessed to make sure it is up to thedesigned specification, and appropriate adjustments should be made and repairs undertaken whennecessary.

• If a water-cooling tower is used, regular cleaning and sterilisation should be carried out to preventthe growth of micro-organisms. If possible, wind-chilled cooling towers should be used.

3. Maintenance of Mechanical Ventilation SystemsProper maintenance can reduce the harmful effects of indoor air pollutants on the occupants.

A competent ventilation maintenance agency should be employed to carry out regular inspection,

cleaning, testing and maintenance.

• Dust filters, fans, cooling coil and ventilation ducts should be regularly cleaned or changed.

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4. Fresh Air Supply Rate for General Work Activities in Air-conditionedWorkplaces

Note: At locations where harmful substances may be generated, local exhaust systems should be installed to prevent dispersal.

* Note: Food and Environmental Hygiene Department requires that the fresh air supply rate for restaurants and factorycanteens should be at least 13 to 17 cubic metres per hour per person, or 0.2 to 0.3 cubic metres per minute perperson.

Common Working Areas with a Fixed Number of People

Where daily general work or long stay (such as 8 hours)

Places with Relatively Busy Activities

(m3/min/person)

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The World Health Organisation (WHO) has set certain guidelines for the safeguarding of public health

from the harmful effects of air pollution, and to eliminate or reduce known or suspected pollutants

that have a negative impact on health. As these guidelines do not include categorisations based on the

types of public contact, they sum up the standards for both indoor and outdoor air quality.

WHO Guideline Values for the Exposure Limits of Certain Substances Other

than Cancer or Odour Annoyance

Setting Air Quality Standards

* Exposure to this concentration should not exceed the time indicated and should not be repeated within8 hours.

# This refers to indoor air only

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Tips on Improving Indoor Air Quality

1 Through the dilution of outdoor air• The minimum fresh air supply rate is

guaranteed;

• The minimum indoor air replacement rate isreached;

2 The location of the inlet for outdoor air• Do not locate the air inlet near any known

source of pollution, sewage, or cooling tower;

• Ensure that animals are unable to enter, andprevent birds from roosting or building nests.

If the exhaust outlet of another ventilationsystem is located near the fresh air inlet, exhaustair can easily re-enter the building.

If the cooling tower isinstalled at inappropriatel o c a t i o n s , b a c t e r i a -contaminated dew caneasily be carried to thenearby fresh air inlet.

• The supply of fresh air required is assessedaccording to the concentration of indoor airpollutants;

• Direct exhaust of air from indoor pollutionsources is guaranteed.

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3 Location of Exhaust Vent• The exhaust vent should be located away from the fresh air inlet, and should be positioned in a

relatively high location;

• The exhaust vent should face in the opposite direction to the fresh air inlet.

4 Control of Micro-organisms• The accumulation of condensation in the air-conditioning system should be avoided;

• The humidifier, temperature control unit, fan, filter, ventilation duct and cooling tower should beregularly cleaned.

5 Distribution of Air• The formation of stagnant air areas (unventilated

areas) as well as air stratification should beavoided;

Any interference with the free flow ofincoming fresh air and exhaust air will resultin air pollutants accumulating in a stagnantarea without being dispersed.

Out-of-balance air-conditioning systems will resultin some places being too hot and other placesbeing too cold. Blocking the air-inlet louvres willfurther throw the system out of balance.

6 Control of Indoor Air Pollutants• Suitable furniture should be selected

to minimize pollution by volatileorganic compounds;

When decorating officebuilding materials, furnitureand carpets made ofnon-volatile chemicalcompounds should be used.

• Air mixing should be made to take place in the breathing zone of occupants;

• Appropriate air pressure should be maintained for designated areas (for example, smoking roomsshould have negative air pressure);

• The correct balance between air inlets and extractor systems should be maintained.

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• Non-smoking areas should be designatedin order to protect employees from theharmful effects of environmental tobaccosmoke;

A policy restricting smokingin the office should beimplemented.

• Regular cleaning and pest control can reducethe accumulation of dust and the breeding ofmicro-organisms;

Carpets should be cleaned frequently, andsubjected to sterilisation and pest control.

Furniture covers should bewashed frequently.

Air freshening equipment only acts as atemporary measure in improving air quality.Ultimately, the basic cause of any poor air qualityshould be identified and remedial measures taken.

• Indoor air-purification systems can help eliminateair pollutants;

The indoor temperature should bemaintained between 23˚C and 26˚C insummer and 20˚C and 25˚C in winter.The relative humidity should be keptbetween 40% and 70%.

Carbon filters can be installed toeliminate odours.

• The proper use of local control units, whichare part of the central air-conditioningsystem, should be made to make theworking environment more comfortable.