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Causes of sick building syndrome 

Despite numerous investigations, journal articles and conferences, little has actually been proven about the causes of sick building syndrome. Different experts have different theories - some say the main cause is chemicals, others that fungi are primarily to blame, or physical factors such as humidity, temperature or lighting, or the air-conditioning system itself.

In the USA, investigations carried out up to the end of 1983 by the National Institute for Occupational Safety and Health (NIOSH), a governmental organisation, showed 'inadequate ventilation' to be the causal factor in about half of buildings with health complaints (see Table 4). Inadequate ventilation was often given as the cause when no other, more precise, cause, could be found.

What is certain is that symptoms are more common in buildings with air-conditioning or mechanical ventilation. Six building features are strongly associated with symptoms of sick building syndrome (McIntyre and Sterling 1982):

a hermetically sealed, airtight shell mechanical heating, ventilation and air-conditioning systems use of materials and equipment that give off a variety of irritating and sometimes toxic fumes and/or dust fluorescent lighting that may produce photochemical smog application of energy conservation measures lack of individual control over environmental conditions

The rest of this chapter looks in more detail at some of the effects of these features.

Table 4: Types of problem found in 203 indoor air quality investigations carried out by NIOSH

Source: Melius 1984

Airborne pollutants

Nearly everything we use sheds particles or gives off gases, particularly when new. People shed dead skin and hair all the time. Clothing, furnishings, curtains, carpets etc. contribute fumes, fibres and other fragments. Cleaning processes such as sweeping, vacuuming and dusting may remove the larger particles but often increase the levels of smaller, respirable, particles in the air. Chemicals used for cleaning are often toxic, and office supplies and equipment may also give off harmful chemicals.

Buildings are complex environments which can trap and concentrate pollutants as well as generate them. Outside pollutants find their way into buildings through air intakes and inadequate filtering systems. As long as ample ventilation ensures a constant supply of fresh air, indoor pollution problems may be kept to a minimum. But general ventilation is often inadequate and office equipment may have no local exhaust system venting fumes to the outside.

The A-Z list below contains some of the more common pollutants that may be found inside buildings and is compiled mainly from information supplied by the Queensland and Lidcombe Workers' Health Centres (1984) and the Northern Trade Union Health and Safety Centre (1989). It is not an exhaustive list of the many thousands of chemicals present in the environment.

When air monitoring for any of these substances is carried out, levels are likely to be below those considered to be 'acceptable' or 'safe'. However, little is known about the health effects of long-term exposure to low levels of a variety of chemicals and some people are sensitive to extremely low concentrations of toxic agents.

Ammonia

Cleaning solutions, blueprint machines (plan printers) and cigarette smoke are sources of ammonia. This gas irritates mucous membranes and so affects the respiratory system and eyes.

Asbestos

There are many sources of asbestos in buildings (e.g. pipe lagging, ceiling and roof tiles, asbestos cement sheeting) particularly in buildings constructed in the 1960s and early 1970s. In the air-conditioning system, asbestos may be used as duct insulation, as mounting for heating elements, or sprayed as insulation in the air-conditioning plant room. The inevitable deterioration of these asbestos products with time means that respirable fibres will be released into the air. Asbestos - blue, brown and white types - can cause cancer and fibrosis of the lung and mesothelioma (cancer of the lining of the chest and abdomen).

Benzene

This cancer-causing chemical is released from synthetic fibres and plastics, and is found in cleaning solutions and tobacco smoke. It damages the central nervous system and skin, and causes respiratory irritation.

Biocides

Biocides are added to air-conditioning systems to control the growth of micro-organisms. They are also toxic to humans; the effect depends on the biocide. Biocides and other chemical water treatments such as anti-scaling agents should not be used in humidifiers or in any part of the air-conditioning system where they may be picked up in the airstream and so breathed by workers.

Carbon dioxide

Carbon dioxide is present in the unpolluted atmosphere at a concentration of about 0.03 per cent but since about 5 per cent of the air we breathe out is carbon dioxide the level increases in inadequately ventilated occupied rooms. The level of carbon dioxide is therefore often used to assess the efficiency of ventilation, although NIOSH investigators did not find it useful for this purpose (Melius 1984). Levels higher than 800 parts per million (ppm) indicate that the ventilation rate is inadequate. Outside sources include vehicle exhaust fumes, nearby smoking chimneys or other exhausts.

The effects of too much carbon dioxide are headache and lethargy; then breathlessness, sweating, visual impairment and tremor. Finally unconsciousness develops as the level increases.

Carbon monoxide

Any process of combustion can produce carbon monoxide, so this gas is produced by tobacco smoking, gas cookers, and gas or oil heaters. We all exhale a small amount of carbon monoxide in our breath. A major source of carbon monoxide is vehicle exhaust fumes.

Carbon monoxide harms the body by replacing oxygen in the haemoglobin of red blood cells and so starving the body - and the brain in particular - of oxygen. Less than 1 per cent of the haemoglobin of non-smokers is normally bound to carbon monoxide rather than oxygen but this increases to 4-6 per cent in smokers (Hoover 1982). Non-smokers who spend their 8-hour working day in an atmosphere containing 30 parts per million (ppm) of carbon monoxide will also develop a 5 per cent concentration and possibly the early symptoms of carbon monoxide poisoning such as headache. Smokers would not be affected since their bodies have become habituated to such a high level. At levels of 50-250 ppm dizziness may accompany the headache, and above 500 ppm nausea and vomiting occur and collapse is possible. Long-term exposure to carbon monoxide is associated with heart disease.

It has been recommended that carbon monoxide levels be kept below 9 ppm in offices because of the potential for health effects associated with long-term exposure to low levels of this gas (Queensland and Lidcombe Workers' Health Centres 1984). In the UK the occupational exposure limit for carbon monoxide is 50 ppm.

Detergent dust

Detergent residues from carpet cleaning may cause respiratory irritation such as cough, dry throat, breathing difficulty, nasal congestion and headache. Effects depend on the type of detergent used and its formulation.

Ethanol (ethyl alcohol)

Fibreglass

Fibreglass is use for insulation. Large fibres can cause itching and skin irritation; smaller fibres are suspected of causing lung diseases and cancer in a manner similar to asbestos.

Formaldehyde

Formaldehyde is found in hundreds of different products, including insulation material, ceiling tiles, particle board, plywood, office furniture, carpet glues, various plastics, synthetic fibres in rugs, upholstery and other textiles, pesticides, paint and paper. It is also emitted from electric stencil-cutting machines and is present in tobacco smoke. Levels of emission increase with temperature.

Formaldehyde is a colourless gas with a pungent odour. At 2-3 parts per million (ppm) it will irritate the eyes, nose and throat of most people exposed to it, but many are affected at much lower levels. At 4-5 ppm the irritation is worse and is accompanied by drowsiness, loss of memory, sneezing and skin rashes. At 10-20 ppm there is severe breathing difficulty and burning eyes, nose and throat. Formaldehyde increases the risk of several types of cancer, and has also been shown to cause poor sleep, impaired memory, lack of concentration, nausea and menstrual irregularities.

The occupational exposure limit in the UK is 2 ppm, twice as high as the permissible level in the USA of 1 ppm, which has an action level of 0.5 ppm. In Sweden and Germany the maximum permissible indoor level is 0.1 ppm. People who have become sensitised to formaldehyde have adverse reactions whenever it is present, even in very small amounts. Concentrations as low as 0.01 ppm have been associated with eye irritation (HSE 1981)

Hydrocarbons

Chemicals composed of hydrogen and carbon are found in various sources including paints, solvents, synthetic materials, floor and furniture polishes, and vehicle exhaust fumes. Their effect on health depends on the type of hydrocarbon but can include respiratory, skin and eye irritation, nausea, headache, central and peripheral nervous system damage, and cancer.

Hydrogen chloride

Hydrogen chloride is emitted by electric stencil-cutting machines. It irritates the mucous membranes of eyes, nose and throat.

Methanol (methyl alcohol)

Methanol is used in spirit duplicating machines, and causes irritation to the eyes, respiratory system and skin.

Micro-organisms

Not much research has been carried out on indoor pollution with microbes such as bacteria and fungi (mould). In the USA, investigation of more than 200 governmental, hospital and commercial buildings showed that 34 per cent had high levels of fungi and 9 per cent had high levels of bacteria which could potentially cause disease or allergy (Robertson 1988). The fungal species Aspergillus and Cladosporium were found growing to excess in the ductwork of many of the buildings where workers had high levels of symptoms. In some cases, 'challenge' tests were carried out which showed that these workers had severe allergic reactions to the spores of these fungi. Subsequent cleaning and removal of the sources of contamination apparently cleared up the symptoms (Robertson 1988).

Micro-organisms are probably responsible for humidifier fever and extrinsic allergic alveolitis, which are discussed elsewhere, and for legionnaires' disease (see Chapter 3).

Motor vehicle exhaust

Exhaust fumes contain carbon monoxide, nitrogen oxides, lead particulates, sulphur oxides and hydrocarbons. Sources include basement car-parks which don't have their own separate ventilation system and outside traffic. The siting of ventilation intakes is therefore important in determining the intake of exhaust fumes into the building.

Nitrogen oxides

Like carbon monoxide, nitrogen oxides are produced as products of combustion, so sources include vehicle exhausts, tobacco smoke and gas heaters. These chemicals cause irritation to the respiratory system and eyes.

Ozone

Ozone is naturally present in the air since it is produced from oxygen by ultraviolet radiation. However, it can also be produced by electrical discharges and is emitted by some items of electrical equipment such as photocopiers and electrostatic precipitators (devices used to 'clean' the air by removing dust). A single photocopying machine can produce more than 0.1 parts per million (ppm), which is the recommended limit for exposure to ozone in the UK and Australia.

Ozone is a dangerous gas since it mimics the effects of ionising radiation (X-rays and gamma-rays) and can cause genetic damage. It is also very irritating to mucous membranes in eyes, nose and throat (at 0.1 ppm), causing lung damage at higher exposures. It can also cause headache (at 1 ppm), dizziness and severe fatigue. No one should work in the same room as a photocopier which is in constant use or employed for long runs, particularly if unvented.

Ozone is sometimes added to the air-conditioning system to 'sweeten' the air and counteract smells. This should never be done: an adequate supply of fresh air is what is needed.

Paint

Paint fumes, depending on the formulation, may cause headache and irritation to the eyes and respiratory system, damage to the nervous and reproductive systems, and kidney and bone marrow injury at high exposure levels.

PCBs (polychlorinated biphenyls)

Use of these dangerous chemicals, which include dioxin and dibenzofuran, is now banned in the UK, but they may still be found in electrical appliances and may leak from ageing visual display units and fluorescent lights. PCBs cause skin rashes, cancer, foetal defects, and damage to reproductive organs, liver and kidney.

Pesticides

Pesticides may be used inside buildings for many reasons: to kill fungi, beetles, fleas, ants, booklice, silverfish, rodents, and plant and timber pests. Although all pesticides are harmful to humans (some more than others), treatment is sometimes carried out during working hours, with little apparent concern for the health of the people working at their desks. Or spraying may be carried out overnight or over the weekend so that the chemical is still circulating in the atmosphere when workers return to the building. The pesticides used as wood preservatives often leach out into the air over a number of years.

Pesticides may be added to air-conditioning and ventilation systems to reduce biological contamination. This is not the way to effect control: proper cleaning and maintenance are what is needed, or the chemicals will be circulated around the building.

The hazards of pesticides depend on their chemical constituents (often a 'cocktail' of chemicals is used) and include cancer, foetal damage, liver and neurological damage, skin problems, and irritation to the eyes and respiratory system.

Photochemical smog

It is possible that the various individual pollutants may combine to form new hazards, and it has been suggested that ultraviolet light from fluorescent tubes provides energy for reactions to occur between ozone and other chemicals.

Radon

Radon is a decay product of uranium and is present in varying amounts in the soil. It moves from the soil by diffusion into the soil's air pockets and into soil water, from where it can migrate through building foundation cracks etc. into the indoor space. Building materials such as concrete and stone may also contain radon. Out-gassing from these materials, and from radon in the water supply, adds to the indoor air levels derived primarily from the soil below the building.

The effects of high levels of radon on humans are those associated with ionising radiation (X-rays and gamma-rays): cancer and damage to the reproductive organs and to the fetus. The effects of low levels of exposure are not known but the Institution of Environmental Health Officers recently recommended a 50 per cent reduction in the levels considered to be 'safe' for homes in the UK.

Solvents

Solvents such as toluene, acetone and trichloroethane are found in white-out fluids and thinners. They may cause headaches and dizziness or eye, throat and skin irritation. Solvents are also found in adhesives, glues, cleaning fluids, paint and felt-tip pens. Trichloroethylene, which can cause liver cancer and damage to be lungs and central nervous system, is used in spray adhesives and some types of stencil machine.

Sterilant gases

Gases such as ethylene oxide are sometimes used in an attempt to sterilise humidification and air-conditioning systems. The effects will depend on the gas used, and may range from irritation of mucous membranes to cancer. Such gases should not be used.

Sulphur oxides

Sulphur oxides, such as sulphur dioxide which is emitted from coal-burning power stations, chimneys and vehicle exhausts, form acidic solutions when in contact with moisture.

Exposure to sulphur dioxide causes respiratory irritation, runny nose and cough. Long-term exposure can lead to chronic bronchitis, lung damage, altered sense of smell and may act in the presence of other chemicals to produce a cancer-causing effect (co-carcinogenesis).

Tobacco smoke

Cigarette smoking is a considerable source of airborne contamination. Amongst other things, tobacco smoke contains carbon monoxide, carbon dioxide, nicotine, formaldehyde, acetaldehyde, acrolein (a strong irritant), ammonia, hydrogen cyanide, nitrogen oxides, coal tars and particulates. Many of these substances have toxic or irritant properties causing symptoms similar to those of sick building syndrome - eye and nose irritation, coughing, breathing difficulties, sore throat and hoarseness, headache, nausea and dizziness - in both smokers and non-smokers. The long-term effects of smoking include lung cancer and heart disease.

Vinyl chloride

Vinyl chloride is found in plastic products such as pipes and light fixtures and in upholstery and carpets. It is a cancer-causing agent and causes skin and lung irritation.

Air-conditioning systems

Air-conditioning is the process of treating air to control its temperature, moisture content (humidity), purity and distribution. Early proponents of air-conditioning believed that they could produce an atmosphere like a 'perpetual spring'. In practice, the air is often not so sweet.

In buildings with no air-conditioning, fresh air enters by natural ventilation or infiltration - through open windows and doors and gaps in window and door frames. Outside wind pressure makes the air circulate inside, and air also rises as it is warmed. In contrast, the windows of buildings with air-conditioning often cannot be opened because the system is so designed that its controls may be 'thrown out' by even one opened window. These buildings are 'sealed' or 'tight'. Air-conditioning systems rely on mechanical ventilation for air distribution.

There are many different types of air-conditioning and ventilation system. The simplest, which is described as 'mechanical ventilation', only filters and distributes ducted air; the air is not 'conditioned' by heating, cooling or humidity control. Table 5 gives an idea of the range of air-conditioning systems. Not all offices have systems with a plant room and ductwork. Some use domestic-style wall units which take in air through the outside wall, condition it and deliver it straight to the office space.

Despite the wide variety of types of system, they all work along similar basic principles (see Figure 00): an air handling unit draws air into the plant (or unit) where it is treated (filtered, cooled, heated, and perhaps humidified or washed) and then blown through ductwork, entering the office space through supply air vents.

In all-air systems, all plant is centralised and the conditioned air is distributed throughout the building by a network of ducts. These systems are inflexible and the ducting for supply and return air is bulky. The other extreme is the local air handling system. Each room may have its own induction or fan-coil unit, perhaps with a fresh air intake through the wall. These systems are more flexible, often with individual controls in each room. In between comes the decentralised system, which is similar to the local system except that a whole zone (a group of rooms, a wing or a floor of a building) is served by one air handling unit.

In practice, the humidification part of the process may not be in operation to save money on energy costs. Ask for a plan of the air-conditioning system or systems operating in your workplace. Trade union safety representatives are entitled to this information under the Safety Representatives and Safety Committees Regulations (see Appendix 5).

Table 5: Air-conditioning systems

Source: Croome-Gale and Roberts 1975

Outside air inlets

The supply air fan draws fresh air into the building through the outside air inlets. The siting of this intake may be critical in determining how 'fresh' the air actually is. City air can hardly be called fresh, but it may be additionally polluted if the inlet is located in the basement car-park, at pavement level along a busy main road or next to a flowerbed (where pesticides may be sprayed), downwind of a hospital incinerator or chemical plant, or next to a cooling tower or exhaust on the roof. The positioning of fresh air inlets must take into account prevailing wind directions and wind patterns caused by nearby buildings. Inlets should be louvred or wired to prevent birds, large insects and wind-blown debris from entering, and should slope so that rainwater drains away and does not enter the mixing chamber.

Mixing chamber

Here the outside air is mixed with return air from the building. It is usually intended that 10-20 per cent of the air mixture is fresh, but the fresh air dampers may be closed completely so that 100 per cent recycled air is being circulated.

In the USA, ACVA, a commercial organisation that specialises in sick buildings, found that over 35 per cent of 223 buildings it investigated were taking in no fresh air and 64 per cent had inadequate fresh air intake (Robertson 1988).

Filters

Filters are supposed to remove dust and other impurities from the air but are often inefficient or so poorly maintained that they actually pollute the air. In many air-conditioning systems the filters are designed only to stop large insects such as moths and butterflies. There are several different types of filter which vary in their efficiency.

A good filter system will have more than one filter, perhaps including a coarse pre-filter, and the selection will be based on:

anticipated dust load type of dust (e.g. soot, ashes, earth, sand, fibres, animal, vegetable and mineral matter, mould spores, bacteria, viruses, pollen, industrial pollutants) size of dust particles (larger particles settle out on desks etc., smaller particles remain airborne or 'stick' to other surfaces due to electrostatic attraction) degree of cleanliness required

Filters in common use are dry filters, wet filters and electrostatic filters:

Dry filters are usually disposable and made from a fabric or paper-type material which can trap larger dust particles in the airstream. There are two types: the roller type works like a film in a camera, automatically moving on to the next 'frame' when loaded with dirt. The panel type needs to be cleaned and reused or discarded once soiled. Wet filters are relatively coarse filters made from fibres, wire mesh, metal turnings or plates and coated with a viscous substance such as oil or grease. Again, there is a self-cleaning roller type and a fixed panel type. They are often washable and reusable. Electrostatic filters are much more efficient than wet or dry filters for both large and small particles. They work by passing the air through an ioniser which gives particles a positive or negative charge. These charged particles then go through a collector where they are attracted to plates of the opposite charge. Older models of electrostatic filter may produce ozone, as may newer models if they are left in operation with no airstream passing through them. (In one office building, workers received a 'blast' of ozone each morning when the air-conditioning system was turned on in the morning because the electrostatic filter had not also been switched off overnight.)

Filters will not work if they are clogged up with dirt: they must be regularly maintained, cleaned or replaced. Only electrostatic and HEPA (high efficiency particulate air) filters will remove bacteria. Beware of HEPA filters that contain asbestos; these should not be used.

Cooling and biological contamination

As well as removing heat, the cooling coil incidentally dehumidifies the air: moisture in the warm air is condensed out on the cold coil and drops collect in a drip tray. Wherever there is water, particularly if it is left standing for a long time, micro-organisms will grow. And wherever micro-organisms will grow, the potential for humidifier fever and extrinsic allergic alveolitis exists. Despite its name, humidifiers are not the only source of the organic dust believed to be the cause of humidifier fever - any dirty, dusty, damp place such as drip trays, ductwork, evaporative cooling systems, spray cooling devices (air washers) and baffle plates may be a source. These parts of the air-conditioning system are also those where the legionnaires' disease bacterium may grow, and more details on biological contamination are given in Chapter 3 (pages 00-00). [Please give the air-conditioning equipment pages of legionnaires' chapter]

Control systems

There are as many different systems to control the temperature, humidity and delivery rate of the air as there are air-conditioning systems - each building will be unique, and some computer-controlled systems are very complex. The siting and number of thermostats, humidistats and other sensors is crucial to the functioning of the system.

In a variable air volume (VAV) system, when the temperature of the office deviates from the 'set' temperature (perhaps because more people are present) the thermostat automatically controls baffles in the ducting to allow more or less air into the space to maintain the set temperature. Thermostats need to be re-set monthly depending on the average monthly temperature outside since people's bodies acclimatise to different temperatures in different seasons and they dress for the weather.

Temperature problems in buildings may result from:

Wrongly placed thermostats. Sometimes thermostats are located in a passage or at the periphery of an open-plan office where there is solar gain, so that the core of the office remains cold. Rearrangement of office partitions may place the thermostat outside the area it is meant to serve. Faulty thermostat Faulty air-conditioning equipment

Some thermostats are really only 'dummies'. They have no actual effect on ambient temperature but are cynically introduced to give workers the impression that they have some control over the system.

In the UK the use of carbon dioxide monitors to control the amount of fresh air being drawn into the system is luckily not common. Such monitors may be set to operate at levels of carbon dioxide that are never reached, e.g. 2500 parts per million, so that outside air is never introduced.

Delivery and circulation of air

Fans deliver the air to the office space via supply vents (diffusers) sited on the wall or ceiling. The number of fans depends on the size of the building, zoning, etc. An air-conditioned building may be 'zoned' so that varying amounts of air are delivered to different parts of the building. For example, the west side may be given more air in the afternoon to counteract the effects of the sun on room temperature.

Supply air vents (diffusers) control the volume, velocity and direction of air flow into the workspace. Although an adequate amount of air may be delivered to the office, this does not guarantee that the air will circulate to reach everyone equally. Tall furniture such as filing cabinets and acoustic screens, especially those that extend to the floor even if they are no higher than 5 feet, may prevent the air from circulating. Walls and partitions put up to enclose workstations or cellular offices in an area originally designed to be open plan can mean that air delivered at the perimeter never reaches into the open-plan core. To allow air flow, partitions should clear the floor by 1-2 inches. If full-height partitions are used, there must be at least one supply vent (diffuser) and one return or exhaust vent.

The air-conditioning system must be checked once the office floor has been filled up with furniture, partitions and people to ensure that it still delivers and returns air in the way it was designed to. This is called 'balancing' the system. Balancing is often carried out inadequately, or not at all. All air handling systems should be re-balanced after a year or two, depending on how much reorganisation of the floor space there is, and after changes of occupancy.

Exhaust air

Air removal is as important as air supply. Air that has circulated through the office space is returned through ceiling vents, often combined with light fittings, into ducts or plenums. The majority of the exhaust air goes back to the mixing chamber, but a small amount leaves the building through ventilation grilles. Fans in the return air duct draw in the exhaust air. It is possible for air to be drawn directly from the supply to the exhaust vent so that people sitting at desks don't receive any fresh air at all.

In some systems, heat exchangers are used to reclaim heat that would otherwise be exhausted from a space. The wheel of a rotary heat exchanger passes from the exhaust to the supply airstream, alternately absorbing and giving up heat, so heating supply air in the winter and cooling it in summer. Pollutants are transferred to the supply air by these devices (Schaeffler et al 1988).

To maintain air movement, air-conditioned buildings usually operate under slight positive pressure, which means that the pressure inside the building is greater than that outside and there is a tendency for air to move outwards. If the air-conditioning system is faulty and the building is under negative pressure, the efficiency of exhaust fans will be reduced and outside air will infiltrate anywhere it can, perhaps 'rushing in' when windows are opened. The effect of this is that pollutants will not be ventilated out of the building.

Types of problem found

Youle (1986) has found that air-conditioning systems giving rise to symptoms of sick building syndrome can be put into four categories:

Under-designed systems. Examples include no extraction fan, faulty design of fresh air/return air damper, poor temperature control due to centralised plant and inadequate terminal re-heaters, no provision for humidification. Poorly installed, operated and maintained systems. Typical problems found in buildings where systems have not been set up and tested properly include: incorrect function of local control systems, tolerances on temperature control sensors set too wide, incomplete closure of valves to local re-heater batteries, faulty setting of diffusers, malfunctioning humidifier, corrosion of fresh air damper bearings, illogical control system, inadequate operator training. Equipment problems. Sometimes problems related to one particular item of equipment can lead to overall problems of control. For example, air handling units may not be capable of delivering the required amount of air, electronic temperature controls may be malfunctioning, heating or cooling batteries may be the wrong size, diffusers may be of poor quality causing noise and poor control of air flow. Poor control of fresh air. Reduced levels of fresh air input and build-up of contaminants can be due to: closing fresh air dampers to 'save energy', faulty operation of automatic dampers, inadequate purging of the building before occupancy, inadequate overall ventilation, poor air circulation, and low air flow rates in variable air volume systems.

Air quality and thermal comfort

In a comfortable environment there are no noticeable fluctuations in temperature, no stuffiness, draughts, odours, etc. The main factors influencing comfort include temperature, humidity (moisture level) and air movement. These factors interact. For example, if the air is very humid, the temperature appears to be warmer than it would be in drier air. If the air is circulating rapidly, the temperature seems to be cooler than it would be in sluggish air. People don't usually notice comfortable and constant conditions. Problems arise when fluctuations occur such as sudden blasts of cold air.

As all office workers know, different people feel comfortable under different conditions; one person will be too hot when another is 'just right'. In general, women tend to like slightly higher air temperatures than men. But many problems in offices arise because of lack of personal control over the conditions - windows can't be opened, heating can't be locally controlled, lighting is uniform and not task-oriented, table fans aren't allowed in hot weather, etc.

Table 6 gives the levels of various parameters recommended by the Chartered Institution of Building Services Engineers (CIBSE).

Table 6: Comfort levels recommended by the Chartered Institution of Building Services Engineers (CIBSE 1986)

Temperature

Complaints about the temperature in offices are common, particularly if the building is air-conditioned. Some parts of the building might be too cold, while others are too hot, or the air does not circulate properly so that people's feet are always cold even though their faces are warm enough, or the temperature might vary dramatically during the day.

CIBSE recommends a temperature of between 19 and 23 ├C for offices, although temperatures at the lower end of this range (19-21├C) have been suggested to be better since people feel less fatigue at cooler temperatures, which in turn feel 'fresher' (Vischer 1989). Conversely, air that is too warm is experienced as 'stuffy' and possibly as being polluted. Temperatures in offices are often too high, particularly in summer due to the effects of solar gain and heat generated by equipment (thermal radiation). Air-conditioning systems use more energy in cooling the air than heating it.

Air temperature can be checked with an ordinary dry bulb thermometer to see whether it falls within a comfortable range but for a more accurate measurement of comfort, humidity and the speed of air movement also need to be taken into account.

Humidity

Humidity is the amount of moisture in the air. Air at a given temperature can hold only a certain amount of moisture, and no more. This is called 'saturation humidity'. Humidity is measured as a percentage of this saturation humidity (100 per cent) and is referred to as 'relative humidity'.

The higher the relative humidity, the less able the body is to evaporate moisture (sweat) from the skin. At high humidity (above 60-70 per cent) and in warm temperatures, the body produces sweat but is unable to evaporate it so that the air temperature feels hotter than it actually is and you feel 'sticky'. When the relative humidity is low, the air is dry and moisture evaporates easily from the skin. However, when the relative humidity is very low (below about 20 per cent) the skin and mucous membranes of the nose and throat dry out. Dry skin becomes itchy, and scratching can lead to dermatitis. Dry mucous membranes mean a greater susceptibility to infection. Other symptoms of low humidity include headaches, a feeling of stuffiness, sinus troubles and sore eyes.

Dry air also increases problems with static electricity such as skin irritation, minor shocks and face rashes. (Workers at Kensington and Chelsea Town Hall in West London used to water with carpets every morning to cut down the static!)

There is controversy in the UK about the need to humidify the air. Some UK studies have shown that humidified buildings have slightly higher rates of sick building syndrome than non-humidified buildings (Wilson and Hedge 1987) or those with natural ventilation (Harrison et al 1987). But others, carried out in Finland where the air in winter may be extremely dry with relative humidities below 10 per cent, have shown a different association: workers in humidified rooms had fewer symptoms of sick building syndrome than those with no humidification (Jaakkola et al 1988; Reinikainen et al 1988).

Those who oppose humidification in the UK say that relative humidity in this country rarely reaches very low levels and that most people cannot tell whether the air is humidified or not since human beings cannot 'sense' moisture content (McIntyre 1980; Office Secretary 1988). However, a UK study that looked at how well people's ratings of air quality compared with readings from monitoring instruments showed that ratings of 'too dry' correlated well with low measured relative humidities (Wilson et al 1987).

Despite these opposing views, and because of the problems associated with dry air, it seems reasonable to adhere to the CIBSE recommendation of a minimum relative humidity of 40 per cent and to try to maintain a relative humidity of 40-50 per cent. At relative humidities higher than this, the growth of bacteria and moulds in the ventilation system is encouraged because of condensation in the ductwork (Vischer 1989), although higher humidities may be needed if static build-up is a particular problem. Humidifiers can certainly do more harm than good if they are not properly cleaned and maintained.

It must not be forgotten that temperature and relative humidity should be combined to obtain optimal thermal comfort: the higher the relative humidity the lower the air temperature can be for an equivalent sensation of warmth.

Ventilation

Air movement

The faster the movement of air, the cooler it will seem because heat is lost as sweat evaporates into the cooler airstream - as long as the air is not warmer than the body (37├C, which is unlikely in the UK) or the relative humidity is not extremely high. As Table 6 shows, if the air speed is too low the room will feel stuffy and if it is too high the office area will be draughty. Air movement greater than 0.8 metres per second will disturb office papers. Workers sitting next to supply air vents (diffusers) may be annoyed by fast air movement, particularly a ceiling-mounted diffuser that blows air down the back of their necks.

Fresh air

to satisfy the respiratory needs of the occupants to remove body odours and tobacco smoke to maintain the bodily heat balance to control airborne contamination

Several standards have been set for ventilation rates in offices, and they are usually based on the amount of air needed to dilute cigarette smoke or body odour. CIBSE's standard ranges from a minimum of 8 litres of outdoor air per second per person in a general office to 25 litres per second per person where there is heavy smoking in a meeting or conference room. So, if there are 20 workers in an office, the minimum amount of 'fresh air' required is 20 x 8 = 160 litres per second. Fresh air means air from outside the building, not air that has simply been recirculated without any treatment to remove odours, fumes and other contaminants. If the air has a constant odour, smells stale, or workers are suffering from headache or tiredness, then lack of fresh air or lack of air movement could be the cause. To find out whether the fresh air intake meets the CIBSE recommendations, the building services engineer or other person responsible for maintenance of the ventilation system would need to be consulted. These ventilation rates are rarely found in naturally ventilated offices.

In the USA, ventilation standards are based on 80 per cent of occupants failing to 'express dissatisfaction' with the air quality. This means that at acceptable ventilation rates up to 20 per cent of workers could be affected by contaminants from office equipment, new furnishings and outdoor sources and yet the building would still remain within the standard. In many buildings in the UK it is likely that fresh air input is below recommended values (Youle 1986).

Thermal radiation

The radiation of heat from various sources has an important effect on room temperature. Solar radiation through windows and heat from equipment such as lights and visual display units (VDUs) increases the temperature. A person doing clerical work gives out about 140 watts of energy as heat, whereas the heat output of a VDU can be as much as 500 watts. When new equipment is introduced, often no thought is given to upgrading the ventilation to meet the new demands placed on the system; an additional local air-conditioning system may be needed. Devices such as internal blinds made from translucent material that allows the transmission of light but not heat may be used to counteract the effect of solar radiation.

Noise

Noise is rarely mentioned in connection with sick building syndrome since it has not been found to be significantly associated with reports of building sickness (Wilson et al 1987). Yet noise is a facet of office life that people find particularly stressful and which certainly affects their concentration.

Noise that is too loud for comfort is intrusive whether it is a single, unexpected sound or a continuous one. But noise can also be too soft so that workers experience stress from being too easily overheard; a continuous soft noise can also be distracting.

There are several sources of noise in buildings: building-related noises such as buzzing lights, noises from air-conditioning equipment; noise from outside the building; noise from office equipment; and 'people noise'. People's tolerance to building noise may be different from their tolerance to people noise since these are separate acoustical experiences.

Air-conditioning equipment may be noisy if it is functioning poorly or is badly maintained or designed. A rapid flow of air through supply air vents is also noisy; by making ducts larger, the required amount of air can still be supplied through the vent. Ventilation ductwork can also transmit noise around the building, and proper insulation of noisy areas and machinery is needed to reduce these sources of noise.

CIBSE recommends 46 dBA (decibels, 'A' refers to a particular decibel scale on the sound level meter) as the upper sound limit for general office work. Sometimes the background level of noise in a building, i.e. before occupation, reaches this level. During the working day all eight buildings in one study had average sound levels above the CIBSE limit (Wilson et al 1987).

Lighting

Unlike noise, lighting is significantly associated with reports of sick building syndrome (Wilson et al 1987; Vischer 1989). If the workplace is not suitably lit, visual disturbance can occur. Tiredness, dry and gritty eyes and headaches can be caused by glare, flicker, lack of contrast, inadequate illumination or unsuitable spot lighting. Conventional white fluorescent lighting in particular is likely to cause eyestrain and headaches (Wilkins et al 1988) and should be replaced with non-fluorescent lighting and as much daylight as possible. Workers who are unable to negotiate to get rid of their fluorescent tubes should at least press for regular maintenance of lights and for full-spectrum fluorescent tubes to be used since these seem less likely to cause symptoms of sick building syndrome (London 1987; Wilkins et al 1988). (Read the booklet Fluorescent Lighting: A health hazard overhead by the London Hazards Centre for more detailed information.)

CIBSE gives recommendations for the levels of light needed to carry out different types of work (see Table 6). Since a range of activities takes place in offices, an important aspect of lighting design is that individual workers have control over the lighting in their immediate environment. This means that local task lighting is needed as well as good general overhead lighting, particularly where VDUs are in use.

Ions

Many claims have been made about the effects of air ions on health but little 'scientifically acceptable' research on ions has actually been carried out. There is even controversy over the exact nature of ions, although they are usually described as positively or negatively charged forms of the molecules that make up the atmosphere.

It seems that all living things need ions to survive. Scientists in the USSR tried to raise small animals in air containing no ions at all and found that all the mice, rats, guinea-pigs, rabbits, etc. died within a few days. Similar experiments on plants produced stunted growth. One of the few controlled experiments carried out on humans in the UK showed that increasing the number of negative ions in a computer-operating area reduced complaints of headache, nausea and dizziness, and resulted in a significant improvement in the rating of environmental quality. The workers also felt more comfortable and alert. Effects were most marked for those on the night shift (Hawkins 1984). Other workers have failed to reproduce these findings.

The number of negative ions in the atmosphere seems to be more important than the number of positive ions. Research worldwide has associated lack of negative ions with a range of diseases including thrombosis, haemorrhage, asthma and bronchial diseases, difficulty in breathing, aching joints, migraines, insomnia and increased susceptibility to infections. It has also been connected with depression, lethargy, anxiety, mental hospital admissions, suicides and crimes of violence. In contrast, an excess of negative ions is reputed to be associated with feelings of calmness, alertness and well-being, with quicker recovery from exhausting exercise, more appetite, sounder sleep, fewer bodily aches and pains, and fewer respiratory complaints.

Not everyone is sensitive to changes in air ion concentration: about 25 per cent of people notice no difference when the proportion of positive to negative ions is changed. Women seem to be more sensitive to ion depletion than men and respond more favourably to an ion-enriched environment (Hawkins 1984). Negative ions seem to become less effective as the ambient temperature increases above 22├C and at high relative humidities.

The typical air-conditioned office in the city has only 50 negative ions per millilitre of air (and 150 positive ions) compared with 1000 negative ions (and 1200 positive ions) in the same volume of clean, outdoor, country air. Hawkins (1984) gives the reasons for low air ion levels indoors as:

Ducted air conditioning. Metal ducting attracts charged particles so that ions are stripped out of the air as it passes through the ductwork. (Electrostatic filters would similarly reduce ion levels.) Static electricity. In an air-conditioned building, especially one with low humidity, static charges build up on carpets, furniture, wall fabrics, workers' clothing and, particularly, on electrical equipment such as VDU screens. Ions in the room are then attracted to these static charges. Smoke and contamination. Smoke and dust particles act as a sponge, mopping up ions. High density of individuals. Each person removes ions from the air while breathing and each carries an amount of static electricity.

No-one knows how or why air ions may exert their effects. Many of the symptoms of negative ion depletion are similar to the effects of stress on the body, so it may be that the body's hormonal system is affected.

So how can the effects of low levels of negative ions be counteracted? It is clear that ion depletion can be minimised by taking steps to reduce the amount of static electricity in the environment, using natural rather than synthetic fibres wherever possible, making sure that all VDUs and other equipment likely to build up a static charge are properly earthed, controlling humidity and temperature, removing pollutants and dust at source, and ensuring that offices are not overcrowded. Negative ionisers help to clean the air by precipitating dust, fibres and particles out of the atmosphere - as can be seen by the enormous amount of dirt streaking the area that immediately surrounds the ioniser. So, if ionisers are to be introduced as a means of giving workers individual control over their immediate working environment, ensure that proper cleaning arrangements are made to cope with the resulting dirt. This may involve the cleaners working extra time.

Radiation and visual display units

The possible involvement of electromagnetic radiation in sick building syndrome is probably even more controversial in the UK than the effects of air ions, but some people do believe it to be a factor (Best 1989).

The term radiation is used to describe electrical and magnetic energy travelling in the form of waves. These waves differ enormously in frequency (how many go past a given point in a second), and range from the extremely low frequencies given off by electrical appliances operating at high voltages through the visible spectrum of light to the very high frequencies of X-rays and gamma-rays of nuclear fall-out. Radiation of different frequencies has different biological effects.

There are various items of equipment in offices that emit electromagnetic radiation, but the item of most concern in the 1990s is the visual display unit (VDU) which gives out low levels of radiation across a wide range of frequencies. Pulsed low-level radiation at 'biological' frequencies (those that coincide with frequencies used by the body's own electrical systems - nerves) has been shown to affect the behaviour of monkeys and cats, making them lethargic and sleepy at some frequencies and hyperactive at others. Exposure to low levels of ionising radiation (X-rays and gamma-rays) can cause a disease of the thyroid gland, hypothyroidism, which results in lethargy, loss of IQ and an increase in weight (Bertell 1985). In the USSR, several effects have been observed in people exposed to large doses of low frequency radiation, including listlessness, excitability, headache, drowsiness and fatigue. More about the hazards of radiation from VDUs can be found in the VDU Hazards Handbook published by the London Hazards Centre.

One study showed that increased building sickness symptoms occurred only when people spent more than six hours a day working at a VDU (Wilson and Hedge 1987). However, if exposure to radiation is a factor in sick building syndrome, this figure is open to question since, depending on the layout of the room, people who spend no time at all at a VDU may actually have higher exposures than those working on the screen: many VDUs emit more radiation from the side and back than from the front.

Of course, quite apart from the radiation question, work at a VDU is well known to produce some of the symptoms associated with sick building syndrome - eyestrain, sore eyes, skin rashes, headache and fatigue. Other complaints made by VDU workers include an increase in colds, flu and other viral infections; asthma, bronchitis, sinusitis and other respiratory disorders; digestive upsets; angina and other heart and circulatory problems; migraine attacks; irregular or painful periods; miscarriages and birth defects; depression, sometimes suicidal; irritability; exhaustion; going off sex; nausea, loss of appetite or compulsive eating; and insomnia (London Hazards Centre 1987). It may well be that workers reporting such symptoms are working in sick buildings as well as spending far too much time in front of the VDU screen.

'My office is open plan and very crowded. This has been reported to our health and safety officer, but as yet with no results. We now have VDU terminals on one in four desks and by Christmas there will be a terminal on each desk. We use laser printers which are in the middle of the office and smell awful.

I suffer from sinus headaches. At home, I get very few headaches but at work they increase, and I know this occurs with others. Colds spread round the office like a non-stop event, summer and winter.' (Bradford, West Yorkshire)

For ways to improve conditions of VDU work, read the VDU Hazards Handbook. [Now VDU Work and the Hazards to health]

Stress

As this chapter has shown, almost every aspect of the work environment may contribute to the symptoms of sick building syndrome. Figure 00 shows how the various stressors to which people are exposed can affect health, morale and productivity. Chemicals in the building, lack of ventilation, thermal conditions, acoustics and lighting, the nature of the work and other factors all contribute to the stress load on an individual or group of workers.

Some environmental stressors have a direct action (e.g. temperature, humidity, light and noise) causing a physiological response in the body as it tries to regain its equilibrium. But other stressors act in a more subtle, indirect way. For instance, a person may become tense or anxious if they cannot control the environment around them. Being unable to control the temperature to suit your own needs, to change the level of lighting, to open a window for fresh air, to reduce noise, or to eliminate cigarette smoke from the atmosphere is likely to affect your behaviour, causing stress that ultimately takes its toll on your health.

Study after study on sick building syndrome has shown that the amount of control that people have over their environment is critical. Only 4 per cent of people in air-conditioned buildings feel that they have any control over ventilation and over temperature, compared with 33 per cent and 17 per cent respectively in naturally/mechanically ventilated buildings (Wilson and Hedge 1987). However, none of these figures is particularly encouraging, and it is clear that architects and heating, ventilation and lighting engineers have a long way to go before they start creating buildings that are geared to the needs of those who work in them.

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