Indoor Air Quality (IAQ)

The author of this module is
Sarah Porter
image of Indoor Air Quality (IAQ)

Occupational Health Considerations

Indoor air pollutants include: environmental tobacco smoke (ETS); allergens, including moulds; indoor penetration of pollutants from outside (notably particles); cooking fumes; settled dust; asbestos; micro-organisms (e.g. Legionella); endotoxins; nitrogen dioxide (NO2) from fuel burning appliances and gas cookers; carbon monoxide (CO) from faulty gas appliances; ozone; kerosene products; biomass fuel combustion (e.g. plant material, agricultural waste); VOCs (e.g. formaldehyde); and radon. In the developed world, most individuals spend around 90% of their time indoors, and are therefore exposed to the indoor environment to a much greater extent than to the outdoors. In parts of the developing world, much greater time is spent outdoors. In developing countries, reliance on wood, coal, dung and crop waste for cooking a heating via simple stoves is a significant cause of lung disease and cancer. Workplace indoor air quality (IAQ) is affected by many factors. These include poor ventilation (including anything that can affect fresh air coming into a building), thermal factors (difficulties controlling temperature), and extremes of humidity (high or low). On some occasions, poor IAQ may be caused by specific contaminants (for example, dust from construction, mould, cleaning products, pesticides, or other airborne chemicals). In the developing world, use of indoor stoves adversely affects IAQ. Control of Indoor Air Quality Indoor air quality is generally not subject to legislation except in the workplace, where occupational exposure standards apply in some settings. In the UK, the Workplace (Health, Safety and Welfare) Regulations 1992 cover a basic requirement for sufficient ventilation and thermal comfort, with the Approved Code of Practice suggesting a minimum working temperature of 16C (or 13C if physical effort is required). A meaningful figure cannot be given for higher workplace temperatures, as factors other than air temperature (i.e. radiant temperature, humidity and air velocity) become more significant, and interaction between them more complex, with rising temperatures.   Many countries have generalised legislation pertaining to the control of hazardous substances: The UK Control of Substances Hazardous to Health Regulations 2002 are derived from EU-wide legislation and specify occupational exposure limits for certain dust, chemical and biological compounds. There are currently no other indoor air quality standards in the UK. This pattern of legislation is also common elsewhere. There is regulation regarding ventilation outside the work environment. In the UK, for example, classrooms are required to have 2.5 outdoor air changes per hour. In halls, gym, dining, and physiotherapy spaces, the ventilation should be sufficient to limit carbon dioxide to 1,500 ppm. However in the US, ventilation in classrooms is based on the amount of outdoor air per occupant plus the amount of outdoor air per unit of floor area, not air changes per hour. In the control of IAQ, guidance is more common than specific legislation: In the UK for example, the Health and Safety Executive (HSE) has published guidance for employers, building owners and building managers on how to deal with Sick Building Syndrome (HSG132, 3rd edition published in 2000). Suggested management strategies include: optimisation of the physical environment (attention to standards of lighting, temperature and humidity; allowing adequate space to work; regular cleaning to minimise nuisance dust); addressing known risk factors for stress and any psychosocial hazards (promote good industrial relations and communication; increase control-demand ratio where possible); and investigating specific issues (for example, odours).

Clinical Aspects

Good indoor air quality (IAQ) is important for worker comfort and health. Various symptoms have been attributed to poor IAQ, including fatigue, impairment of concentration, headaches, and mucosal/respiratory tract irritation (affecting eyes, nose, throat and lungs). Indoor air pollution has been linked to increased risk of respiratory disease (pneumonia, COPD) and lung cancer, and may also increase risk of cardiovascular disease and stroke. Some diseases have been linked to specific air contaminants or environmental factors, for example asthma with damp indoor environments. Some exposures, such as asbestos and radon, do not cause immediate symptoms but may lead to cancer many years later. Health effects from ETS exposure include respiratory disease and lung cancer. Biomass fuel health effects include chronic bronchitis/COPD and lung cancer.  Cooking fume health effects include lung cancer and possibly exacerbation of asthma. Radon health effects include lung cancer. Volatile Organic Compounds These are organic compunds with high vapour pressures at room temperature such as formaldehyde (ubiquitous in office environments, due to off-gassing from furniture, carpet adhesive and other fixtures made from particle board). Many VOCs are known irritants at high exposure levels; some have low odour thresholds, contributing to a perception of poor air quality, irrespective of actual health effects. VOCs are regulated in the EU, China, US and other countries, often rather loosely. In HK for example only guidance is issued regarding sampling and control of VOCs. Measurement of VOCs in the workplace is typically done with a dedicated digital device measuring a defined small set of VOCs meaning that the presence of more toxic vapours can not be excluded. Such an assay is therefore a marker of air quality and should not be used as an absolute scientific standard. Asbestos Asbestos is a group of naturally occurring silicate minerals, comprising chrysotile, crocidolite, amosite, fibrous actinolite, fibrous anthophyllite and fibrous tremolite, or mixtures containing these. Exposure is subject to regulatory control. Historically, asbestos has been used widely for fire protection and insulation. It is inexpensive, and has many favourable properties (it is flexible, strong and durable, and fire, heat and corrosion resistant). Currently, exposure mainly occurs during the renovation or demolition of old buildings (asbestos insulation, lagging and roof tiles). Although asbestos related disease was first identified in the 1920s, asbestos continued to be used for many years.  Many developed nations have banned the use of asbestos in new construction projects, including the EU, Hong Kong, Japan, Australia and New Zealand.  Notable exceptions that still permit asbestos use are China, Russia, India, Brazil, Canada and the USA. In the UK, the use of asbestos materials was totally banned in 1985, with second-hand reuse, import and sales illegal since 1999. In Australia, the use of crocidolite (blue) asbestos was banned in 1967, while amosite (brown) asbestos continued to be used by the construction industry until the mid-1980s. In the USA, the Environmental Protection Agency issued the Asbestos Ban and Phase Out Rule in 1989, however some continued use of asbestos in construction is permitted (for example, cement asbestos pipes). In developing nations, the widespread use of asbestos continues unabated.   In the UK, the Control of Asbestos Regulations 2012 replaced the Control of Asbestos Regulations 2006 and covers most work with asbestos in the UK (with the 2012 Regulations introducing a third category of work, notifiable non-licensed work, in addition to the existing categories of licensed and non-licensed work). In the UK, the control limit for asbestos is 0.1 fibre/cm3 over any 4-hour period, with exposure not to exceed 0.6 fibres/cm3 in any 10-minute period. Clearance sampling of enclosed areas is required after asbestos removal. In the UK, workers who are currently exposed to asbestos above a defined action level must undergo regular health surveillance (2-yearly lung function) by a doctor appointed by the HSE (CXRs are not required as part of routine health surveillance). Individuals who have been exposed previously need not undergo surveillance, however it is important to document previous exposure carefully (including historical hygiene measurements, if available), and inform the GP with the individuals consent so that exposure is noted in the event of future asbestos-related disease. The individuals should also be counselled regarding the risk of asbestos-related disease and availability of compensation. Key health effects are asbestosis, pleural disorders (mesothelioma; diffuse pleural thickening; benign pleural effusion; pleural plaques), lung cancer and laryngeal cancer. Latency periods are long, potentially in excess of 50 years. In the UK, asbestosis is notifiable under RIDDOR 1995. Smoking cessation should be strongly encouraged in workers exposed to asbestos, as risk of lung cancer from smoking and asbestos is multiplicative. Affected workers may have access to compensation. In Europe, occupational diseases are typically compensated through no-fault systems (workers compensation or social security), rather that tort-based systems prevalent in the USA. Significant variation in asbestos compensation schemes exists between different countries in Europe. In the UK, this may include Industrial Injuries Disablement Benefit (some asbestos-related disorders are prescribed, according to exposure activities), the War Pensions Scheme (asbestos-related disease as a result of exposure while working in HM Forces), and civil compensation (if a worker can prove negligence on the part of their employer; potential claims must be declared within 3 years of the diagnosis of asbestos-related disease). Radon Radon is a colourless, odourless radioactive gas originating from rocks and soil. The radon level in outdoor air is low, but can be higher inside buildings. Radon is everywhere, with some geographic locations more likely to have high levels in buildings (geological surveys produce data sets and maps of radon prone areas, for example those produced by the British Geological Survey). Formal measurement of radon levels is recommended if you live or work in a radon affected area. High levels of radon can cause lung cancer, particularly in smokers and ex-smokers, with risk increased by level and duration of exposure. Work environments vary greatly in size and nature, with the potential for excessive levels of radon in almost any type of workplace. The amount of radon that collects in a building depends on its location, structure and use. In workplaces such as offices, where hazards are normally low, radon can be the largest occupational health risk. Workers who live nearby may also be exposed to a high radon level while at home. All workplaces in radon affected areas should be tested, unless a detailed assessment shows good reason to expect the radon level to be low. Search services are available to find out if premises are in an affected area. If the radon level in any part of a workplace exceeds 300 Bq m-3 as an annual average, Ionising Radiation Regulations apply, obliging the employer to take action. As radon comes from the ground, underground areas are more likely to have high levels. Any frequently occupied basements should also be tested, regardless of whether or not they are in an affected area. Specialist advice should be sought for wholly underground workplaces such as mines, tunnels and caves, and if there are internal sources of radon such as geological samples. Inside buildings, radon levels depend on the amount of ventilation and nature of the work. Radon levels can vary greatly within a large building, with individual risk therefore dependent on the radon level in the different areas where workers spend most of their time. In principle, radon may be prevented from accumulating in premises with particularly high influx of fresh air, but measurement is still required unless a risk assessment can show that the radon level at a particular location is necessarily low at all times when it is occupied. Radon levels can vary over time. This may be due to changes to the construction of the building, or alterations to heating and ventilation caused by a change in use. For this reason, radon should remain in routine risk assessment reviews. If a radon reduction system has been installed to reduce high levels, those systems may fail over time, with annual radon measurement recommended. Mould Moulds are the most common form of fungi, reproducing through spore formation, which float through indoor and outdoor air on a continual basis. When mould spores land on a moist surface indoors, they may grow and ultimately destroy the surface they grow on, with the potential for structural damage. Moulds can be found in all environments, frequently detected by sight (all colours) and smell (musty, earthy odour). Environmental factors increasing risk include dampness, high humidity (relative humidity >70% for prolonged periods), and temperatures above around 20oC. It is impossible to eliminate all moulds and spores in the indoor environment, with moisture control is the most important strategy for reducing indoor mould growth. Moulds, their fragments, and metabolic by-products are associated with adverse health effects. Some diseases are known to be caused by specific moulds, however in many occupational settings health conditions suspected to be mould-related cannot be linked to a specific mould as the only possible cause. Most people experience no health effects from exposure to moulds present in indoor air. However, some individuals with underlying health conditions may be more sensitive to moulds, particularly individuals who are immunosuppressed, have other allergies or existing respiratory conditions such as asthma, sinusitis, or other lung diseases. The most common health effects associated with mould exposure include allergic symptoms (immediate or delayed onset), eye irritation, rhinorrhoea, sneezing, nasal congestion, cough, wheeze, exacerbation of asthma and skin rash. These symptoms are also common allergic responses to other agents. The term building-related illness (BRI) is used to describe illnesses characterized by objective clinical findings related to specific exposures in the indoor environment. In general, the relationships between poor indoor air quality due to the presence of mould and BRIs are unclear. This stems, in part, from the lack of standardized methods by which to measure mould exposures and their effects. However, widespread symptoms related to a building may lead to environmental investigation, mitigation activities, and relocation of occupants. Mould-related BRIs result from mould contamination occurring in buildings under specific conditions, particularly among susceptible individuals. Terms such as Sick Building Syndrome (SBS) have been used to describe situations in which building occupants experience a variety of symptoms for which, unlike BRIs, no specific illness or cause can be identified. Health effects from exposure to mould contamination in indoor environments include common allergic BRIs (allergic rhinitis; allergic asthma; and hypersensitivity pneumonitis, also known as extrinsic allergic alveolitis), and infections (histoplasmosis; cryptococcosis). Mycotoxins can also produce toxin-mediated adverse health effects. In the UK, extrinsic alveolitis associated with exposure to moulds and fungal spores in certain work activities is reportable under RIDDOR legislation. Mould control and remediation: Moisture control is key to mould control. The most important initial step in prevention is visual inspection of the building envelope and drainage systems. Ventilation systems should be checked regularly, particularly for damp filters and overall cleanliness. Preventative maintenance plans should be put into place for each major component of building ventilation systems, including air duct cleaning. Remediation includes both identification and correction of the conditions permitting mould growth, in addition to steps to safely and effectively remove mould-damaged materials. Remediation plans should include steps to permanently correct the moisture problem, cover the use of appropriate PPE, and include steps to safely contain and remove mouldy materials in a manner that avoids further contamination. The work area (and potentially directly adjacent areas, dependent on size) should be unoccupied. Mould damaged materials should be discarded in plastic bags; any porous items that have been wet for >48 hours should also be discarded. Exhaust fans with high-efficiency particulate air (HEPA) filtration may be required. Appropriate PPE should be used to prevent contamination and skin contact with moulds and chemicals used to decontaminate (long gloves; approved respiratory protection, normally a half-face or full-face respirator as a minimum; eye protection with non-vented goggles; protective clothing such as disposable coveralls). Where visible mould is present, clean-up can proceed on the basis of visual inspection, with sampling not usually necessary. Sampling and analysis of mould is complex and expensive, with a lack of standard procedures for sampling and analysis. There are currently no regulatory or professional recommendations for airborne concentrations of mould, mould spores, mycotoxins, and other bioaerosols with which to compare any sampling results. However, sampling for mould may be considered in the following situations: when medical diagnosis is consistent with mould-associated illness; to delimit the outer boundaries of severely contaminated areas before and during a mould clean-up project; after a clean-up, to show that the types and concentrations of mould in the area are similar to background levels. Input from experienced health and safety professionals, working closely with an accredited environmental microbiology laboratory, to determine and document the details of the sampling strategy is advised. Legionella Legionnaires disease is an uncommon infection caused by the bacterium Legionella pneumophilia, an organism living naturally in environmental water sources. Most cases occur sporadically, but outbreaks can occur. Transmission is by inhalation of infected aerosols. In workplaces, L. pneumophilia is found in air-conditioning units, cooling towers and showers. Any workers in air-conditioned buildings might be affected, as may occupational travellers staying in hotels exposed to infected droplets in showers. The incubation period is 2-19 days (median 6-7 days). It presents as an influenza-like illness, with fatigue, fever, headache, myalgia, dry cough, diarrhoea and confusion. Atypical pneumonia can also develop. Clinical diagnosis is made by rapid urine antigen test, culture of respiratory secretions, and serology. Treatment is with antibiotics (particularly erythromycin). Most cases recover, but 10-15% of infections are fatal, higher in susceptible groups. Susceptible individuals include those aged >50 years, men (3 times more likely to be affected than women), smokers, and those with underlying chronic disease or immunosuppression. Prevention of Legionnaires disease is through treatment of water systems, with detailed specific guidance provided by the UK HSE. In the UK, Legionellosis is reportable under RIDDOR legislation where it occurs associated with work on or near workplace cooling systems which use water, or work on workplace hot water service systems likely to be a source of contamination. Sick building syndrome Sick building syndrome (SBS) occurs in artificially ventilated buildings. The term was first used in the mid-1980s to describe an ill-defined collection of symptoms that are typically reported by workers located in the same building. Despite extensive research, the cause of the syndrome has not been fully explained. It is more common in women, and at the lower end of the organizational hierarchy. Reported symptoms are usually mild but may lead to significant impairment of performance. Symptoms include headache, fatigue, poor concentration, dizziness, nausea, upper respiratory tract symptoms (sore throat, nasal symptoms, more frequent respiratory infections), chest tightness, skin rash/redness, generalised pruritis, and eye discomfort/dryness. Many possible causal factors for SBS have been proposed. Among the factors listed below, some have been associated with SBS in epidemiological studies. Most have a plausible link to some of the common symptoms, but none have been proven to be the cause of SBS at low-level exposure. Potential physical and environmental causative factors include: humidity (either excessively high, encouraging mould formation, or excessively low, leading to mucous membrane drying); excessively high temperature; air conditioning (associated with microbial contamination, exotoxins produced by contaminating organisms, and biocides); poor lighting; and nuisance dusts. Potential chemical causative factors include: VOCs, nitrogen dioxide (primary indoor sources include unvented fuel burning appliances, heating appliances and cigarette smoking); cigarette smoke (passive smoking was a factor in the past, although around the world smoking in public buildings is commonly no longer permissible by law). In China, a study of nearly 2000 school children over two years found a mild association between NO2 and mucosal symptoms and SO2 and general SBS symptoms. Bio-aerosols have also been identified as potential causative factors in SBS. These are airborne particles comprising or contaminated with bacteria, fungi or mites. Potential psychosocial causative factors for SBS include: low control over work; insufficient or excessive demands; low job satisfaction; and poor support. The exact cause of SBS remains unknown. It is likely to have a multifactorial aetiology, with contributions from more than one of the factors listed above. Mechanisms are unclear, but may include allergic (immune-mediated) or non-allergic (non-specific, inflammatory or directly toxic) reactions.

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