Guardino Solá, Xavier

Guardino Solá, Xavier

Address: National Centre for Working Conditions, National Institute for Occupational Safety and Hygiene, Calle Dulcet 2-10, 08034 Barcelona

Country: Spain

Phone: 34 3 280 0102

Fax: 34 3 280 3642

Education: PhD; Master (Env Eng)

Areas of interest: Indoor air quality; toxicology; safety in laboratories; health and safety in health-care

Friday, 11 March 2011 16:56

Smoking Regulations

In regard to taking action to reduce the use of tobacco, governments should keep in mind that while people decide on their own whether they should stop smoking, it is a government’s responsibility to take all the necessary measures to encourage them to stop. The steps taken by legislators and governments of many countries have been indecisive, because while the reduction in the use of tobacco is an undisputed improvement in public health—with attendant savings in public health expenditures—there would be a series of economic losses and dislocations in many sectors, at least of a temporary nature. The pressure that international health and environmental organizations and agencies can exert in this regard is very important, because many countries may water down measures against the use of tobacco because of economic problems—especially if tobacco is an important source of income.

This article briefly describes regulatory measures that can be adopted to reduce smoking in a country.

Warnings on Cigarette Packs

One of the first measures adopted in many countries is to require that cigarette packs prominently display the warning that smoking seriously injures the smoker’s health. This warning, whose aim is not so much to exert an immediate effect on the smoker, but rather to show that the government is concerned about the problem, is creating a psychological climate that will favour the adoption of later measures that otherwise would be considered aggressive by the smoking population.

Some experts advocate the inclusion of these warnings on cigars and pipe tobacco. But the more general opinion is that those warnings are unnecessary, because people who use that type of tobacco do not normally inhale the smoke, and extending these warnings would lead more likely to a disregard of the messages as a whole. This is why the prevalent opinion is that the warnings should be applied only to cigarette packs. A reference to second-hand smoke has not, for the moment, been considered, but it is not an option that should be discarded.

Smoking Restrictions in Public Spaces

Forbidding smoking in public spaces is one of the most effective regulatory instruments. These prohibitions can significantly reduce the number of people exposed to second-hand smoke and, in addition, can reduce smokers’ daily cigarette consumption. The common complaints by owners of public spaces, such as hotels, restaurants, recreational facilities, dance halls, theatres and so forth, are based on the argument that these measures will result in a loss of customers. However, if governments implement these measures across the board, the negative impact of a loss of clientele will occur only in the first phase, because people will eventually adapt to the new situation.

Another possibility is the design of specific spaces for smokers. The separation of smokers from non-smokers should be effective in order to obtain the desired benefits, creating barriers that prevent non-smokers from inhaling tobacco smoke. Separation must thus be physical and, if the air-conditioning system uses recycled air, the air from smoking areas should not be mixed with that from non-smoking areas. Creating spaces for smokers therefore implies construction and compartmentalization expenses, but may be a solution for those who want to serve the smoking public.

Aside from locations where smoking is obviously forbidden for security reasons because of possible explosion or fire, there should also be areas—such as health care and sports facilities, schools and day-care centres—where smoking is not permitted even though there are no safety risks of that kind.

Smoking Restrictions at Work

Smoking restrictions in the workplace may also be considered in light of the above. Governments and business owners, together with trade unions, can establish programmes to reduce the use of tobacco at work. Campaigns to curtail smoking at work are generally successful.

Whenever possible, creating non-smoking areas to establish a policy against tobacco use and to support people who defend the right not to be second-hand smokers is recommended. In case of a conflict between a smoker and a non-smoker, regulations should always allow the non-smoker to prevail, and whenever they cannot be separated, the smoker should be pressured to abstain from smoking at the workstation.

In addition to places where for health or safety reasons smoking should be forbidden, the possibility of synergism between the effects of chemical pollution in the workplace and tobacco smoke should not be ignored in other areas either. The weight of such considerations will result, without a doubt, in a broad extension of smoking restrictions, especially in industrial workplaces.

Greater Economic Pressure against Tobacco

Another regulatory tool governments rely on to curb the use of tobacco is levying higher taxes, chiefly on cigarettes. This policy is intended to lead to lower tobacco consumption, which would justify the inverse relation between the price of tobacco and its consumption and which can be measured when comparing the situation in different countries. It is considered effective where the population is forewarned of the dangers of tobacco use and advised of the need to stop consuming it. An increase in the price of tobacco can be a motivation to quit smoking. This policy, however, has many opponents, who base their criticisms on arguments briefly mentioned below.

In the first place, according to many specialists, the increase in the price of tobacco for fiscal reasons is followed by a temporary reduction in the use of tobacco, followed by a gradual return to the previous consumption levels as the smokers get used to the new price. In other words, smokers assimilate a rise in the price of tobacco much in the same way that people get used to other taxes or to the rise in the cost of living.

In the second place, a shift in the habits of smokers has also been observed. When prices go up they tend to seek out cheaper brands of lower quality that probably also pose a greater risk to their health (because they lack filters or have higher amounts of tar and nicotine). This shift may go so far as to induce smokers to adopt the practice of making home-made cigarettes, which would completely eliminate any possibility of controlling the problem.

In the third place, many experts are of the opinion that measures of this kind tend to bolster the belief that the government accepts tobacco and its consumption as yet another means to collect taxes, leading to the contradictory belief that what the government really wants is that people smoke so that it can collect more money with the special tax on tobacco.

Limiting Publicity

Another weapon used by governments to reduce tobacco consumption is to restrict or simply forbid any publicity for the product. Governments and many international organizations have a policy of forbidding publicity for tobacco in certain spheres, such as sports (at least some sports), health care, the environment, and education. This policy has unquestionable benefits, which are especially effective when it eliminates publicity in those environments that affect young people at a time when they are likely to take up the smoking habit.

Public Programmes that Encourage People to QuitSmoking

The use of anti-smoking campaigns as a normal practice, adequately funded and organized as a rule of conduct in certain spheres, such as the world of work, has been shown to be highly successful.

Campaigns to Educate Smokers

Complementing what was said above, educating smokers so that they will smoke “better” and cut down on their consumption of cigarettes is another avenue available to governments to reduce the adverse health effects of tobacco use on the population. These efforts should be directed at reducing the daily consumption of cigarettes, at inhibiting the inhalation of smoke as much as possible, at not smoking the butts of cigarettes (the toxicity of smoke increases towards the end of the cigarette), at not keeping the cigarette steadily at the lips, and at adopting preferences for brands with lower tar and nicotine.

Measures of this type evidently do not reduce the number of smokers, but they do reduce how much smokers are harmed by their habit. There are arguments against this type of remedy because it may give the impression that smoking is not intrinsically a bad habit, since smokers are told how best to smoke.

Concluding Remarks

Regulatory and legislative action by different governments is slow and not sufficiently effective, especially given what would be required due to the problems caused by tobacco use. Often this is the case because of legal hurdles against implementing such measures, arguments against unfair competition, or even the protection of the individual’s right to smoke. Progress in the use of regulations has been slow but it is nonetheless steady. On the other hand, the difference between active smokers and second-hand or passive smokers should be kept in mind. All the measures that would help someone to stop smoking, or at least to reduce daily consumption effectively, should be directed at the smoker; all the weight of regulations should be brought to bear against this habit. The passive smoker should be given every possible argument to support his or her right not to inhale tobacco smoke, and to defend the right to enjoy the use of smoke-free environments at home, at work and at play.

 

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Wednesday, 09 March 2011 17:05

Indoor Air Quality: Introduction

The connection between the use of a building either as a workplace or as a dwelling and the appearance, in certain cases, of discomfort and symptoms that may be the very definition of an illness is a fact that can no longer be disputed. The main culprit is contamination of various kinds within the building, and this contamination is usually referred to as “poor quality of indoor air”. The adverse effects due to poor air quality in closed spaces affect a considerable number of people, since it has been shown that urban dwellers spend between 58 and 78% of their time in an indoor environment which is contaminated to a greater or lesser degree. These problems have increased with the construction of buildings that are designed to be more airtight and that recycle air with a smaller proportion of new air from the outside in order to be more energy efficient. The fact that buildings that do not offer natural ventilation present risks of exposure to contaminants is now generally accepted.

The term indoor air is usually applied to nonindustrial indoor environments: office buildings, public buildings (schools, hospitals, theatres, restaurants, etc.) and private dwellings. Concentrations of contaminants in the indoor air of these structures are usually of the same order as those commonly found in outdoor air, and are much lower than those found in air in industrial premises, where relatively well-known standards are applied in order to assess air quality. Even so, many building occupants complain of the quality of the air they breathe and there is therefore a need to investigate the situation. Indoor air quality began to be referred to as a problem at the end of the 1960s, although the first studies did not appear until some ten years later.

Although it would seem logical to think that good air quality is based on the presence in the air of the necessary components in suitable proportions, in reality it is the user, through respiration, who is the best judge of its quality. This is because inhaled air is perceived perfectly through the senses, as human beings are sensitive to the olfactory and irritant effects of about half a million chemical compounds. Consequently, if the occupants of a building are as a whole satisfied with the air, it is said to be of high quality; if they are unsatisfied, it is of poor quality. Does this mean that it is possible to predict on the basis of its composition how the air will be perceived? Yes, but only in part. This method works well in industrial environments, where specific chemical compounds related to production are known, and their concentrations in the air are measured and compared with threshold limit values. But in nonindustrial buildings where there may be thousands of chemical substances in the air but in such low concentrations that they are, perhaps, thousands of times less than the limits set for industrial environments, the situation is different. In most of these cases information about the chemical composition of indoor air does not allow us to predict how the air will be perceived, since the combined effect of thousands of these contaminants, together with temperature and humidity, can produce air that is perceived as irritating, foul, or stale—that is, of poor quality. The situation is comparable to what happens with the detailed composition of an item of food and its taste: chemical analysis is inadequate to predict whether the food will taste good or bad. For this reason, when a ventilation system and its regular maintenance are being planned, an exhaustive chemical analysis of indoor air is rarely called for.

Another point of view is that people are considered the only sources of contamination in indoor air. This would certainly be true if we were dealing with building materials, furniture and ventilation systems as they were used 50 years ago, when bricks, wood and steel predominated. But with modern materials the situation has changed. All materials contaminate, some a little and others much, and together they contribute to a deterioration in the quality of indoor air.

The changes in a person’s health due to poor indoor air quality can show up as a wide array of acute and chronic symptoms and in the form of a number of specific illnesses. These are illustrated in figure 1. Although poor indoor air quality results in fully developed illness in only a few cases, it can give rise to malaise, stress, absenteeism and loss of productivity (with concomitant increases in production costs); and allegations about problems related to the building can develop rapidly into conflict between the occupants, their employers and the owners of the buildings.

Figure 1. Symptoms and illnesses related to the quality of indoor air.

AIR010T1

Normally it is difficult to establish precisely to what extent poor indoor air quality can harm health, since not enough information is available concerning the relationship between exposure and effect at the concentrations in which the contaminants are usually found. Hence, there is a need to take information obtained at high doses—as with exposures in industrial settings—and extrapolate to much lower doses with a corresponding margin of error. In addition, for many contaminants present in the air, the effects of acute exposure are well known, whereas there are considerable gaps in the data regarding both long-term exposures at low concentrations and mixtures of different contaminants. The concepts of no-effect-level (NOEL), harmful effect and tolerable effect, already confusing even in the sphere of industrial toxicology, are here even more difficult to define. There are few conclusive studies on the subject, whether relating to public buildings and offices or private dwellings.

Series of standards for outdoor air quality exist and are relied on to protect the general population. They have been obtained by measuring adverse effects on health resulting from exposure to contaminants in the environment. These standards are therefore useful as general guidelines for an acceptable quality of indoor air, as is the case with those proposed by the World Health Organization. Technical criteria such as the threshold limit value of the American Conference of Governmental Industrial Hygienists (ACGIH) in the United States and the limit values legally established for industrial environments in different countries have been set for the working, adult population and for specific lengths of exposure, and cannot therefore be applied directly to the general population. The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) in the United States has developed a series of standards and recommendations that are widely used in assessing indoor air quality.

Another aspect that should be considered as part of the quality of indoor air is its smell, because smell is often the parameter that ends up being the defining factor. The combination of a certain smell with the slight irritating effect of a compound in indoor air can lead us to define its quality as “fresh” and “clean” or as “stale” and “polluted”. Smell is therefore very important when defining the quality of indoor air. While odours objectively depend on the presence of compounds in quantities above their olfactory thresholds, they are very often evaluated from a strictly subjective point of view. It should also be kept in mind that the perception of an odour may result from the smells of many different compounds and that temperature and humidity may also affect its characteristics. From the standpoint of perception there are four characteristics that allow us to define and measure odours: intensity, quality, tolerability and threshold. When considering indoor air, however, it is very difficult to “measure” odours from a chemical standpoint. For that reason the tendency is to eliminate odours that are “bad” and to use, in their place, those considered good in order to give air a pleasant quality. The attempt to mask bad odours with good ones usually ends in failure, because odours of very different qualities can be recognized separately and lead to unforeseeable results.

A phenomenon known as sick building syndrome occurs when more than 20% of the occupants of a building complain about air quality or have definite symptoms. It is evidenced by a variety of physical and environmental problems associated with non-industrial indoor environments. The most common features seen in cases of sick building syndrome are the following: those affected complain of non-specific symptoms similar to the common cold or respiratory illnesses; the buildings are efficient as regards energy conservation and are of modern design and construction or recently remodelled with new materials; and the occupants cannot control the temperature, humidity and illumination of the workplace. The estimated percentage distribution of the most common causes of sick building syndrome are inadequate ventilation due to lack of maintenance; poor distribution and insufficient intake of fresh air (50 to 52%); contamination generated indoors, including from office machines, tobacco smoke and cleaning products (17 to 19%); contamination from the outside of the building due to inadequate placement of air intake and exhaust vents (11%); microbiological contamination from stagnant water in the ducts of the ventilation system, humidifiers and refrigeration towers (5%); and formaldehyde and other organic compounds emitted by building and decoration materials (3 to 4%). Thus, ventilation is cited as an important contributory factor in the majority of cases.

Another question of a different nature is that of building-related illnesses, which are less frequent, but often more serious, and are accompanied by very definite clinical signs and clear laboratory findings. Examples of building-related illnesses are hypersensitivity pneumonitis, humidifier fever, legionellosis and Pontiac fever. A fairly general opinion among investigators is that these conditions should be considered separately from sick building syndrome.

Studies have been done to ascertain both the causes of air quality problems and their possible solutions. In recent years, knowledge of the contaminants present in indoor air and the factors contributing to a decline in indoor air quality has increased considerably, although there is a long way to go. Studies carried out in the last 20 years have shown that the presence of contaminants in many indoor environments is higher than anticipated, and moreover, different contaminants have been identified from those that exist in outside air. This contradicts the assumption that indoor environments without industrial activity are relatively free of contaminants and that in the worst of cases they may reflect the composition of outside air. Contaminants such as radon and formaldehyde are identified almost exclusively in the indoor environment.

Indoor air quality, including that of dwellings, has become a question of environmental health in the same way as has happened with control of outdoor air quality and exposure at work. Although, as already mentioned, an urban person spends 58 to 78% of his or her time indoors, it should be remembered that the most susceptible persons, namely the elderly, small children and the sick, are the ones who spend most of their time indoors. This subject began to be particularly topical from around 1973 onwards, when, because of the energy crisis, efforts directed at energy conservation concentrated on reducing the entry of outside air into indoor spaces as much as possible in order to minimize the cost of heating and cooling buildings. Although not all the problems relating to indoor air quality are the result of actions aimed at saving energy, it is a fact that as this policy spread, complaints about indoor air quality began to increase, and all the problems appeared.

Another item requiring attention is the presence of micro-organisms in indoor air which can cause problems of both an infectious and an allergic nature. It should not be forgotten that micro-organisms are a normal and essential component of ecosystems. For example, saprophytic bacteria and fungi, which obtain their nutrition from dead organic material in the environment, are found normally in the soil and atmosphere, and their presence can also be detected indoors. In recent years problems of biological contamination in indoor environments have received considerable attention.

The outbreak of Legionnaire’s disease in 1976 is the most discussed case of an illness caused by a micro-organism in the indoor environment. Other infectious agents, such as viruses that can cause acute respiratory illness, are detectable in indoor environments, especially if the occupation density is high and much recirculation of air is taking place. In fact, the extent to which micro-organisms or their components are implicated in the outbreak of building-associated conditions is not known. Protocols for demonstrating and analysing many types of microbial agents have been developed only to a limited degree, and in those cases where they are available, the interpretation of the results is sometimes inconsistent.

Aspects of the Ventilation System

Indoor air quality in a building is a function of a series of variables which include the quality of the outdoor air, the design of the ventilation and air-conditioning system, the conditions in which this system operates and is serviced, the compartmentalization of the building and the presence of indoor sources of contaminants and their magnitude. (See figure 2) By way of summary it may be noted that the most common defects are the result of inadequate ventilation, contamination generated indoors and contamination coming from outside.

Figure 2. Diagram of building showing sources of indoor and outdoor pollutants.

AIR010F1

Regarding the first of these problems, causes of inadequate ventilation can include: an insufficient supply of fresh air due to a high level of recirculation of the air or a low volume of intake; incorrect placement and orientation in the building of intake points for outside air; poor distribution and consequently incomplete mixing with the air of the premises, which can produce stratification, unventilated zones, unforeseen pressure differences giving rise to unwanted air currents and continuous changes in the thermohygrometric characteristics noticeable as one moves about the building—and incorrect filtration of the air because of lack of maintenance or inadequate design of the filtering system—a deficiency which is particularly serious where the outdoor air is of poor quality or where there is a high level of recirculation.

Origins of Contaminants

Indoor contamination has different origins: the occupants themselves; inadequate materials or materials with technical defects used in the construction of the building; the work performed within; excessive or improper use of normal products (pesticides, disinfectants, products used for cleaning and polishing); combustion gases (from smoking, kitchens, cafeterias and laboratories); and cross-contamination coming from other poorly ventilated zones which then diffuses towards neighbouring areas and affects them. It should be borne in mind that substances emitted in indoor air have much less opportunity of being diluted than those emitted in outdoor air, given the difference in the volumes of air available. As regards biological contamination, its origin is most frequently due to the presence of stagnant water, materials impregnated with water, exhausts and so on, and to defective maintenance of humidifiers and refrigeration towers.

Finally, contamination coming from outside must also be considered. As regards human activity, three main sources may be mentioned: combustion in stationary sources (power stations); combustion in moving sources (vehicles); and industrial processes. The five main contaminants emitted by these sources are carbon monoxide, oxides of sulphur, oxides of nitrogen, volatile organic compounds (including hydrocarbons), polycyclic aromatic hydrocarbons and particles. Internal combustion in vehicles is the principal source of carbon monoxide and hydrocarbons and is an important source of oxides of nitrogen. Combustion in stationary sources is the main origin of oxides of sulphur. Industrial processes and stationary sources of combustion generate more than half of the particles emitted into the air by human activity, and industrial processes can be a source of volatile organic compounds. There are also contaminants generated naturally that are propelled through the air, such as particles of volcanic dust, soil and sea salt, and spores and micro-organisms. The composition of outdoor air varies from place to place, depending both on the presence and the nature of the sources of contamination in the vicinity and on the direction of the prevailing wind. If there are no sources generating contaminants, the concentration of certain contaminants that will typically be found in “clean” outdoor air are as follows: carbon dioxide, 320 ppm; ozone, 0.02 ppm: carbon monoxide, 0.12 ppm; nitric oxide, 0.003 ppm; and nitrogen dioxide, 0.001 ppm. However, urban air always contains much higher concentrations of these contaminants.

Apart from the presence of the contaminants originating from outside, it sometimes happens that contaminated air from the building itself is expelled to the exterior and then returns inside again through the intakes of the air-conditioning system. Another possible way by which contaminants may enter from the exterior is by infiltration through the foundations of the building (e.g., radon, fuel vapors, sewer effluvia, fertilizers, insecticides and disinfectants). It has been shown that when the concentration of a contaminant in the outdoor air increases, its concentration in the air inside the building also increases, although more slowly (a corresponding relationship obtains when the concentration decreases); it is therefore said that buildings exert a shielding effect against external contaminants. However, the indoor environment is not, of course, an exact reflection of the conditions outside.

Contaminants present in indoor air are diluted in the outdoor air that enters the building and they accompany it when it leaves. When the concentration of a contaminant is less in the outdoor air than the indoor air, the interchange of indoor and outdoor air will result in a reduction in the concentration of the contaminant in the air inside the building. If a contaminant originates from outside and not inside, this interchange will result in a rise in its indoor concentration, as mentioned above.

Models for the balance of amounts of contaminants in indoor air are based on the calculation of their accumulation, in units of mass versus time, from the difference between the quantity that enters plus what is generated indoors, and what leaves with the air plus what is eliminated by other means. If appropriate values are available for each of the factors in the equation, the indoor concentration can be estimated for a wide range of conditions. Use of this technique makes possible the comparison of different alternatives for controlling an indoor contamination problem.

Buildings with low interchange rates with outdoor air are classified as sealed or energy-efficient. They are energy-efficient because less cold air enters in winter, reducing the energy required to heat the air to the ambient temperature, thus cutting the cost of heating. When the weather is hot, less energy is also used to cool the air. If the building does not have this property, it is ventilated through open doors and windows by a process of natural ventilation. Although they may be closed, differences of pressure, resulting both from the wind and from the thermal gradient existing between the interior and the exterior, force the air to enter through crevices and cracks, window and door joints, chimneys and other apertures, giving rise to what is called ventilation by infiltration.

The ventilation of a building is measured in renewals per hour. One renewal per hour means that a volume of air equal to the volume of the building enters from outside every hour; in the same way, an equal volume of indoor air is expelled to the exterior every hour. If there is no forced ventilation (with a ventilator) this value is difficult to determine, although it is considered to vary between 0.2 and 2.0 renewals per hour. If the other parameters are assumed to be unchanged, the concentration of contaminants generated indoors will be less in buildings with high renewal values, although a high renewal value is not a complete guarantee of indoor air quality. Except in areas with marked atmospheric pollution, buildings that are more open will have a lower concentration of contaminants in the indoor air than those constructed in a more closed manner. However, buildings that are more open are less energy-efficient. The conflict between energy efficiency and air quality is of great importance.

Much action undertaken to reduce energy costs affects indoor air quality to a greater or lesser extent. In addition to reducing the speed with which the air circulates within the building, efforts to increase the insulation and waterproofing of the building involve the installation of materials that may be sources of indoor contamination. Other action, such as supplementing old and frequently inefficient central heating systems with secondary sources that heat or consume the indoor air can also raise contaminant levels in indoor air.

Contaminants whose presence in indoor air is most frequently mentioned, apart from those coming from outside, include metals, asbestos and other fibrous materials, formaldehyde, ozone, pesticides and organic compounds in general, radon, house dust and biological aerosols. Together with these, a wide variety of types of micro-organisms can be found, such as fungi, bacteria, viruses and protozoa. Of these, the saprophytic fungi and bacteria are relatively well known, probably because a technology is available for measuring them in air. The same is not true of agents such as viruses, rickettsiae, chlamydias, protozoa and many pathogenic fungi and bacteria, for the demonstration and counting of which no methodology is as yet available. Among the infectious agents, special mention should be made of: Legionella pneumophila, Mycobacterium avium, viruses, Coxiella burnetii and Histoplasma capsulatum; and among the allergens: Cladosporium, Penicillium and Cytophaga.

Investigating Indoor Air Quality

Experience so far suggests that the traditional techniques used in industrial hygiene and heating, ventilation and air-conditioning do not always provide satisfactory results at present for solving the ever more common problems of indoor air quality, although basic knowledge of these techniques permits good approximations for dealing with or reducing problems rapidly and inexpensively. The solution to problems of indoor air quality often requires, in addition to one or more experts in heating, ventilation and air-conditioning and industrial hygiene, specialists in indoor air quality control, analytical chemistry, toxicology, environmental medicine, microbiology, and also epidemiology and psychology.

When a study is carried out on indoor air quality, the objectives set for it will profoundly affect its design and the activities directed at sampling and evaluation, since in some cases procedures giving a rapid response will be required, while in others overall values will be of interest. The duration of the programme will be dictated by the time required to obtain representative samples, and will also depend on the season and on meteorological conditions. If the aim is to carry out an exposure-effect study, in addition to long-term and short-term samples for evaluating peaks, personal samples will be required for ascertaining the direct exposure of individuals.

For some contaminants, well-validated and widely used methods are available, but for the majority this is not the case. Techniques for measuring levels of many contaminants found indoors are normally derived from applications in industrial hygiene but, given that the concentrations of interest in indoor air are usually much lower than those occurring in industrial environments, these methods are frequently inappropriate. As for the measurement methods used in atmospheric contamination, they operate with margins of similar concentrations, but are available for relatively few contaminants and present difficulties in indoor use, such as would arise, for example, with a high-volume sampler for determining particulate matter, which on the one hand would be too noisy and on the other could modify the quality of the indoor air itself.

The determination of contaminants in indoor air is usually carried out by using different procedures: with continuous monitors, whole-time active samplers, whole-time passive samplers, direct sampling and personal samplers. Adequate procedures exist at present for measuring levels of formaldehyde, oxides of carbon and nitrogen, volatile organic compounds and radon, among others. Biological contaminants are measured using techniques of sedimentation on open culture plates or, more frequently nowadays, by using active systems that cause the air to impact on plates containing nutrient, which are subsequently cultured, the quantity of micro-organisms present being expressed in colony-forming units per cubic meter.

When a problem of indoor air quality is being investigated, it is usual to design beforehand a practical strategy consisting of an approximation in phases. This approximation begins with a first phase, the initial investigation, which can be carried out using industrial hygiene techniques. It must be structured so that the investigator does not need to be a specialist in the field of indoor air quality in order to carry out his work. A general inspection of the building is undertaken and its installations are checked, particularly as regards the regulation and adequate functioning of the heating, ventilation and air-conditioning system, according to the standards set at the time of its installation. It is important in this respect to consider whether the persons affected are able to modify the conditions of their surroundings. If the building does not have systems of forced ventilation, the degree of effectiveness of the existing natural ventilation must be studied. If after revision—and adjustment if necessary—the operational conditions of the ventilation systems are adequate for the standards, and if despite this the complaints continue, a technical investigation of a general kind will have to ensue to determine the degree and nature of the problem. This initial investigation should also allow an assessment to be made as to whether the problems can be considered solely from the functional point of view of the building, or whether the intervention of specialists in hygiene, psychology or other disciplines will be necessary.

If the problem is not identified and resolved in this first phase, other phases can follow involving more specialized investigations concentrating on potential problems identified in the first phase. The subsequent investigations may include a more detailed analysis of the heating, ventilation and air-conditioning system of the building, a more extensive evaluation of the presence of materials suspected of emitting gases and particles, a detailed chemical analysis of the ambient air in the building and medical or epidemiological assessments to detect signs of disease.

As regards the heating, ventilation and air-conditioning system, the refrigeration equipment should be checked in order to ensure that there is no microbial growth in them or accumulation of water in their drip trays, the ventilation units must be checked to see that they are functioning correctly, the air intake and return systems must be examined at various points to see that they are watertight, and the interior of a representative number of ducts must be checked to confirm the absence of micro-organisms. This last consideration is particularly important when humidifiers are used. These units require particularly careful programmes of maintenance, operation and inspection in order to prevent the growth of micro-organisms, which can propagate themselves throughout the air-conditioning system.

The options generally considered for improving indoor air quality in a building are the elimination of the source; its insulation or independent ventilation; separating the source from those who may be affected; general cleaning of the building; and increased checking and improvement of the heating, ventilation and air-conditioning system. This may require anything from modifications at particular points to a new design. The process is frequently of a repetitive nature, so that the study has to be started again several times, using more sophisticated techniques on each occasion. A more detailed description of control techniques will be found elsewhere in this Encyclopaedia.

Finally, it should be emphasized that, even with the most complete investigations of indoor air quality, it may be impossible to establish a clear relationship between the characteristics and composition of the indoor air and the health and comfort of the occupants of the building under study. Only the accumulation of experience on the one hand, and the rational design of ventilation, occupation and compartmentalization of buildings on the other, are possible guarantees from the outset of obtaining indoor air quality that is adequate for the majority of the occupants of a building.

 

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Wednesday, 02 March 2011 16:24

Waste Anaesthetic Gases

The use of inhaled anaesthetics was introduced in the decade of 1840 to 1850. The first compounds to be used were diethyl ether, nitrous oxide and chloroform. Cyclopropane and trichloroethylene were introduced many years later (circa 1930-1940), and the use of fluoroxene, halothane and methoxiflurane began in the decade of the 1950s. By the end of the 1960s enflurane was being used and, finally, isoflurane was introduced in the 1980s. Isoflurane is now considered the most widely used inhalation anaesthetic even though it is more expensive than the others. A summary of the physical and chemical characteristics of methoxiflurane, enflurane, halothane, isoflurane and nitrous oxide, the most commonly used anaesthetics, is shown in table 1 (Wade and Stevens 1981).

Table 1. Properties of inhaled anaesthetics

 

Isoflurane,
Forane

Enflurane,
Ethrane

Halothane,
Fluothane

Methoxyflurane,
Penthrane

Dinitrogen oxide,
Nitrous oxide

Molecular weight

184.0

184.5

197.4

165.0

44.0

Boiling point

48.5°C

56.5°C

50.2°C

104.7°C

Density

1.50

1.52 (25°C)

1.86 (22°C)

1.41 (25°C)

Vapour pressure at 20 °C

250.0

175.0 (20°C)

243.0 (20°C)

25.0 (20°C)

Smell

Pleasant, sharp

Pleasant, like ether

Pleasant, sweet

Pleasant, fruity

Pleasant, sweet

Separation coefficients:

Blood/gas

1.40

1.9

2.3

13.0

0.47

Brain/gas

3.65

2.6

4.1

22.1

0.50

Fat/gas

94.50

105.0

185.0

890.0

1.22

Liver/gas

3.50

3.8

7.2

24.8

0.38

Muscle/gas

5.60

3.0

6.0

20.0

0.54

Oil/gas

97.80

98.5

224.0

930.0

1.4

Water/gas

0.61

0.8

0.7

4.5

0.47

Rubber/gas

0.62

74.0

120.0

630.0

1.2

Metabolic rate

0.20

2.4

15–20

50.0

 

All of them, with the exception of nitrous oxide (N2O), are hydrocarbons or chlorofluorinated liquid ethers that are applied by vapourization. Isoflurane is the most volatile of these compounds; it is the one that is metabolized at the lowest rate and the one that is least soluble in blood, in fats and in the liver.

Normally, N2O, a gas, is mixed with a halogenated anaesthetic, although they are sometimes used separately, depending on the type of anaesthesia that is required, the characteristics of the patient and the work habits of the anaesthetist. The normally used concentrations are 50 to 66% N2O and up to 2 or 3% of the halogenated anaesthetic (the rest is usually oxygen).

The anaesthesia of the patient is usually started by the injection of a sedative drug followed by an inhaled anaesthetic. The volumes given to the patient are in the order of 4 or 5 litres/minute. Parts of the oxygen and of the anaesthetic gases in the mixture are retained by the patient while the remainder is exhaled directly into the atmosphere or is recycled into the respirator, depending among other things on the type of mask used, on whether the patient is intubated and on whether or not a recycling system is available. If recycling is available, exhaled air can be recycled after it is cleaned or it can be vented to the atmosphere, expelled from the operating room or aspirated by a vacuum. Recycling (closed circuit) is not a common procedure and many respirators do not have exhaust systems; all the air exhaled by the patient, including the waste anaesthetic gases, therefore, ends up in the air of the operating room.

The number of workers occupationally exposed to waste anaesthetic gases is high, because it is not only the anaesthetists and their assistants who are exposed, but all the other people who spend time in operating rooms (surgeons, nurses and support staff), the dentists who perform odontological surgery, the personnel in delivery rooms and intensive care units where patients may be under inhaled anaesthesia and veterinary surgeons. Similarly, the presence of waste anaesthetic gases is detected in recovery rooms, where they are exhaled by patients who are recovering from surgery. They are also detected in other areas adjacent to operating rooms because, for reasons of asepsis, operating rooms are kept at positive pressure and this favours the contamination of surrounding areas.

Health Effects

Problems due to the toxicity of anaesthetic gases were not seriously studied until the 1960s, even though a few years after the use of inhaled anaesthetics became common, the relationship between the illnesses (asthma, nephritis) that affected some of the first professional anaesthetists and their work as such was already suspected (Ginesta 1989). In this regard the appearance of an epidemiological study of more than 300 anaesthetists in the Soviet Union, the Vaisman (1967) survey, was the starting point for several other epidemiological and toxicological studies. These studies—mostly during the 1970s and the first half of the 1980s—focused on the effects of anaesthetic gases, in most cases nitrous oxide and halothane, on people occupationally exposed to them.

The effects observed in most of these studies were an increase in spontaneous abortions among women exposed during or before pregnancy, and among women partners of exposed men; an increase in congenital malformations in children of exposed mothers; and the occurrence of hepatic, renal and neurological problems and of some types of cancer in both men and women (Bruce et al. 1968, 1974; Bruce and Bach 1976). Even though the toxic effects of nitrous oxide and of halothane (and probably its substitutes as well) on the body are not exactly the same, they are commonly studied together, given that exposure generally occurs simultaneously.

It appears likely that there is a correlation between these exposures and an increased risk, particularly for spontaneous abortions and congenital malformations in children of women exposed during pregnancy (Stoklov et al. 1983; Spence 1987; Johnson, Buchan and Reif 1987). As a result, many of the people exposed have expressed great concern. Rigorous statistical analysis of these data, however, casts doubt on the existence of such a relationship. More recent studies reinforce these doubts while chromosomal studies yield ambiguous results.

The works published by Cohen and colleagues (1971, 1974, 1975, 1980), who carried out extensive studies for the American Society of Anaesthetists (ASA), constitute a fairly extensive series of observations. Follow-up publications criticized some of the technical aspects of the earlier studies, particularly with respect to the sampling methodology and, especially, the proper selection of a control group. Other deficiencies included lack of reliable information on the concentrations to which the subjects had been exposed, the methodology for dealing with false positives and the lack of controls for factors such as tobacco and alcohol use, prior reproductive histories and voluntary infertility. Consequently, some of the studies are now even considered invalid (Edling 1980; Buring et al. 1985; Tannenbaum and Goldberg 1985).

Laboratory studies have shown that exposure of animals to ambient concentrations of anaesthetic gases equivalent to those found in operating rooms does cause deterioration in their development, growth and adaptive behaviour (Ferstandig 1978; ACGIH 1991). These are not conclusive, however, since some of these experimental exposures involved anaesthetic or subanaesthetic levels, concentrations significantly higher than the levels of waste gases usually found in operating room air (Saurel-Cubizolles et al. 1994; Tran et al. 1994).

Nevertheless, even acknowledging that a relationship between the deleterious effects and exposures to waste anaesthetic gases has not been definitively established, the fact is that the presence of these gases and their metabolites is readily detected in the air of operating rooms, in exhaled air and in biological fluids. Accordingly, since there is concern about their potential toxicity, and because it is technically feasible to do so without inordinate effort or expense, it would be prudent to take steps to eliminate or reduce to a minimum the concentrations of waste anaesthetic gases in operating rooms and nearby areas (Rosell, Luna and Guardino 1989; NIOSH 1994).

Maximum Allowable Exposure Levels

The American Conference of Governmental Industrial Hygienists (ACGIH) has adopted a threshold limit value-time weighted average (TLV-TWA) of 50 ppm for nitrous oxide and halothane (ACGIH 1994). The TLV-TWA is the guideline for the production of the compound, and the recommendations for operating rooms are that its concentration be kept lower, at a level below 1 ppm (ACGIH 1991). NIOSH sets a limit of 25 ppm for nitrous oxide and of 1 ppm for halogenated anaesthetics, with the additional recommendation that when they are used together, the concentration of halogenated compounds be reduced to a limit of 0.5 ppm (NIOSH 1977b).

With regard to values in biological fluids, the recommended limit for nitrous oxide in urine after 4 hours of exposure at average ambient concentrations of 25 ppm ranges from 13 to 19 μg/L, and for 4 hours of exposure at average ambient concentrations of 50 ppm, the range is 21 to 39 μg/L (Guardino and Rosell 1995). If exposure is to a mixture of a halogenated anaesthetic and nitrous oxide, the measurement of the values from nitrous oxide is used as the basis for controlling exposure, because as higher concentrations are used, quantification becomes easier.

Analytical Measurement

Most of the procedures described for measuring residual anaesthetics in air are based on the capture of these compounds by adsorption or in an inert bag or container, later to be analysed by gas chromatography or infrared spectroscopy (Guardino and Rosell 1985). Gas chromatography is also employed to measure nitrous oxide in urine (Rosell, Luna and Guardino 1989), while isoflurane is not readily metabolized and is therefore seldom measured.

Common Levels of Residual Concentrations in the Air of Operating Rooms

In the absence of preventive measures, such as the extraction of residual gases and/or introducing an adequate supply of new air into the operating suite, personal concentrations of more than 6,000 ppm of nitrous oxide and 85 ppm of halothane have been measured (NIOSH 1977). Concentrations of up to 3,500 ppm and 20 ppm, respectively, in the ambient air of operating rooms, have been measured. The implementation of corrective measures can reduce these concentrations to values below the environmental limits cited earlier (Rosell, Luna and Guardino 1989).

Factors that Affect the Concentration of Waste Anaesthetic Gases

The factors which most directly affect the presence of waste anaesthetic gases in the environment of the operating room are the following.

Method of anaesthesia. The first question to consider is the method of anaesthesia, for example, whether or not the patient is intubated and the type of face mask being used. In dental, laryngeal or other forms of surgery in which intubation is precluded, the patient’s expired air would be an important source of emissions of waste gases, unless equipment specifically designed to trap these exhalations is properly placed near the patient’s breathing zone. Accordingly, dental and oral surgeons are considered to be particularly at risk (Cohen, Belville and Brown 1975; NIOSH 1977a), as are veterinary surgeons (Cohen, Belville and Brown 1974; Moore, Davis and Kaczmarek 1993).

Proximity to the focus of emission. As is usual in industrial hygiene, when the known point of emission of a contaminant exists, proximity to the source is the first factor to consider when dealing with personal exposure. In this case, the anaesthetists and their assistants are the persons most directly affected by the emission of waste anaesthetic gases, and personal concentrations have been measured in the order of two times the average levels found in the air of operating rooms (Guardino and Rosell 1985).

Type of circuit. It goes without saying that in the few cases in which closed circuits are used, with reinspiration after the cleansing of the air and the resupply of oxygen and the necessary anaesthetics, there will be no emissions except in the case of equipment malfunction or if a leak exists. In other cases, it will depend on the characteristics of the system used, as well as on whether or not it is possible to add an extraction system to the circuit.

The concentration of anaesthetic gases. Another factor to take into account is the concentrations of the anaesthetics used since, obviously, those concentrations and the amounts found in the air of the operating room are directly related (Guardino and Rosell 1985). This factor is especially important when it comes to surgical procedures of long duration.

Type of surgical procedures. The duration of the operations, the time elapsed between procedures done in the same operating room and the specific characteristics of each procedure—which often determine which anaesthetics are used—are other factors to consider. The duration of the operation directly affects the residual concentration of anaesthetics in the air. In operating rooms where procedures are scheduled successively, the time elapsed between them also affects the presence of residual gases. Studies done in large hospitals with uninterrupted use of the operating rooms or with emergency operating rooms that are used beyond standard work schedules, or in operating rooms used for prolonged procedures (transplants, laryngotomies), show that substantial levels of waste gases are detected even before the first procedure of the day. This contributes to increased levels of waste gases in subsequent procedures. On the other hand, there are procedures that require temporary interruptions of inhalation anaesthesia (where extracorporeal circulation is needed, for example), and this also interrupts the emission of waste anaesthetic gases into the environment (Guardino and Rosell 1985).

Characteristics specific to the operating room. Studies done in operating rooms of different sizes, design and ventilation (Rosell, Luna and Guardino 1989) have demonstrated that these characteristics greatly influence the concentration of waste anaesthetic gases in the room. Large and non-partitioned operating rooms tend to have the lowest measured concentrations of waste anaesthetic gases, while in small operating rooms (e.g., paediatric operating rooms) the measured concentrations of waste gases are usually higher. The general ventilation system of the operating room and its proper operation is a fundamental factor for the reduction of the concentration of waste anaesthetics; the design of the ventilation system also affects the circulation of waste gases within the operating room and the concentrations in different locations and at various heights, something that can be easily verified by carefully taking samples.

Characteristics specific to the anaesthesia equipment. The emission of gases into the environment of the operating room depends directly on the characteristics of the anaesthesia equipment used. The design of the system, whether it includes a system for the return of excess gases, whether it can be attached to a vacuum or vented out of the operating room, whether it has leaks, disconnected lines and so on are always to be considered when determining the presence of waste anaesthetic gases in the operating room.

Factors specific to the anaesthetist and his or her team. The anaesthetist and his or her team are the last element to consider, but not necessarily the least important. Knowledge of the anaesthesia equipment, of its potential problems and the level of maintenance it receives—both by the team and by the maintenance staff in the hospital—are factors that affect very directly the emission of waste gases into the air of the operating room (Guardino and Rosell 1995). It has been clearly shown that, even when using adequate technology, the reduction of the ambient concentrations of anaesthetic gases cannot be achieved if a preventive philosophy is absent from the work routines of anaesthetists and their assistants (Guardino and Rosell 1992).

Preventive Measures

The basic preventive actions required to reduce occupational exposure to waste anaesthetic gases effectively can be summarized in the following six points:

  1. Anaesthetic gases should be thought of as occupational hazards. Even if from a scientific standpoint it has not been conclusively shown that anaesthetic gases have a serious deleterious effect on the health of people who are occupationally exposed, there is a high probability that some of the effects mentioned here are directly related to the exposure to waste anaesthetic gases. For that reason it is a good idea to consider them toxic occupational hazards.
  2. Scavenger systems should be used for waste gases. Scavenger systems are the most effective technical hardware for the reduction of waste gases in the air of the operating room (NIOSH 1975). These systems must fulfil two basic principles: they must store and/or adequately eliminate the whole volume of air expired by the patient, and they must be designed to guarantee that neither the respiration of the patient nor the proper functioning of the anaesthesia equipment will be affected—with separate safety devices for each function. The techniques most commonly employed are: a direct connection to a vacuum outlet with a flexible regulating chamber that allows for the discontinuous emission of gases of the respiratory cycle; directing the flow of the gases exhaled by the patient to the vacuum without a direct connection; and directing the flow of gases coming from the patient to the return of the ventilation system installed in the operating room and expelling these gases from the operating room and from the building. All these systems are technically easy to implement and very cost-efficient; the use of installed respirators as part of the design is recommended. In cases where systems that eliminate waste gases directly cannot be used because of the special characteristics of a procedure, localized extraction can be employed near the source of emission as long as it does not affect the general ventilation system or the positive pressure in the operating room.
  3. General ventilation with a minimum of 15 renewals/hour in the operating room should be guaranteed. The general ventilation of the operating room should be perfectly regulated. It should not only maintain positive pressure and respond to the thermohygrometric characteristics of the ambient air, but should also provide a minimum of 15 to 18 renewals per hour. Also, a monitoring procedure should be in place to ensure its proper functioning.
  4. Preventive maintenance of the anaesthesia circuit should be planned and regular. Preventive maintenance procedures should be set up that include regular inspections of the respirators. Verifying that no gases are being emitted to the ambient air should be part of the protocol followed when the equipment is first turned on, and its proper functioning with regard to the safety of the patient should be checked. The proper functioning of the anaesthesia circuit should be verified by checking for leaks, periodically replacing filters and checking the safety valves.
  5. Environmental and biological controls should be used. The implementation of environmental and biological controls provides information not only about the correct functioning of the various technical elements (extraction of gases, general ventilation) but also about whether the working procedures are adequate for curtailing the emission of waste gases into the air. Today these controls do not present technical problems and they can be implemented economically, which is why they are recommended.
  6. Education and training of the exposed personnel is crucial. Achieving an effective reduction of occupational exposure to waste anaesthetic gases requires educating all operating room personnel about the potential risks and training them in the required procedures. This is particularly applicable to anaesthetists and their assistants who are most directly involved and those responsible for the maintenance of the anaesthesia and air-conditioning equipment.

 

Conclusion

Although not definitively proven, there is enough evidence to suggest that exposures to waste anaesthetic gases may be harmful to HCWs. Stillbirths and congenital malformations in infants born to female workers and to the spouses of male workers represent the major forms of toxicity. Since it is technically feasible at a low cost, it is desirable to reduce the concentration of these gases in the ambient air in operating rooms and adjacent areas to a minimum. This requires not only the use and correct maintenance of anaesthesia equipment and ventilation/air conditioning systems but also the education and training of all personnel involved, especially anaesthetists and their assistants, who generally are exposed to higher concentrations. Given the work conditions peculiar to operating rooms, indoctrination in the correct work habits and procedures is very important in trying to reduce the amounts of anaesthetic waste gases in the air to a minimum.

 

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