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*-- __ _-- __ - “ _I - NATURAL GAS AND IN I DOMESTIC PREMISES

COMBUSTION DU GAZ NATUREL ET QUALITE DE L’AIR A L’INTERIEUR DES HABITATIONS

Lucian0 Occhio, Angelo Riva Snam, Italy

Franco Canci, Valter Scevarolli Italgas, Italy

ABSTRACT

Indoor air quality depends on many factors; combustion appliances are one of the sources of emissions inside dwellings. Their installation is regulated by UNI-CIG standards which also establish the ventilation and aeration requirements needed to guarantee the safety and healthiness of the environment. In order to critically evaluate the effect on indoor air quality of using gas appliances under different operational regimes and in different types of building, Snam and ltalgas have developed a research project in co-operation with Enitecnologie and Turin Polytechnic, even to provide theoretical and experimental support for standardisation activities. The results of the presented research include experimental measurements made in real buildings, mathematical modelling and analysis of Italian and international literature. The results show that use of combustion appliances has little influence on indoor air quality and does not affect people’s health.

RESUME

La qualit6 de I’air dans les interieurs depend de beaucoup de facteurs ; les appareils de combustion sont une source d’emissions B I’interieur des habitations. Leur installation est reglementee par les normes UNI-CIG qui etablissent aussi les exigences de ventilation et d’aeration afin d’assurer la securite et la salubritk.

Afin d’evaluer quelle est I’influence de I’emploi des appareils A gaz sur la qualite de I’air interieur, pour diverses conditions de fonctionnement et differentes caracteristiques des batiments, Snam et ltalgas ont developpe un projet de recherche en cooperation avec Enitecnologie et le Polytechnique de Turin, en ayant aussi pour but de fournir un support technique et experimental pour I’activite de normalisation.

Ce memoire presente les resultats de cette recherche, qui comprend des mesures experimentales dans des batiments reels, des modelisations mathematiques et une analyse de la litterature nationale et internationale ; on met en evidence que I’utilisation des appareils de combustion a peu d’influence sur la qualite de I’air interieur et qu’elle n’affecte pas la sante des personnes. DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. I.INTRODUCTION

Indoor Air Quality (IAQ) is an important factor in human health and wellbeing. It depends on many factors, including - but not limited to - the quality of outdoor air, the presence of sources inside the dwellings, the physical characteristics of the buildings (volume, air change rate, building materials ...) and on the habits and lifestyles of the people who live in them. Houses are not aseptic environments; they are places where people live and carry out a variety of activities which may cause emission of pollutants. The very presence of the people themselves has an effect on air quality. Reduction in natural or forced ventilation in buildings after energy-saving measures favours accumulation of pollutants within the dwelling. These substances may be chemical (such as volatile organic compounds, carbon monoxide, nitrogen dioxide .. .), physical (asbestos, radon, electromagnetic radiation ...) and biological (fungi, bacteria, pollen, parasites .. .). There are many emission sources in dwellings: the building materials, furniture, people, pets, plants, cigarette smoke, combustion appliances, electrical appliances, the cooking of food, home cleaning products and so on. The paper examines the correlation between use of combustion appliances, which are only one of the emission sources, and indoor air quality, on the basis of the results of experiments, modelling and studies published in the literature, giving the results of measurement programmes in dwellings, with the aim of also providing technical and experimental support for the formulation of standards.

2. COMBUSTION APPLIANCES

2.1 Use of Combustion Appliances

Appliances which burn gas are widely used for cooking, hot water production and heating. In Italy there are over 13 million gas cookers (1996), over 7 million of which work on both gas and electricity, and over 12 million gas heating systems, over 9 million of which are heating systems for individual houses or flats. Appliances and devices powered by gas oil, liquefied petroleum gas and solid fuels are also employed. TABLE 1 shows fuel consumption for domestic use in Italy.

TABLE. 1: FUEL CONSUMPTION IN THE DOMESTIC SECTOR IN ITALY (1996)

(ktoe)

NATURAL GAS OIL OTHER SOLID FUELS GAS PETROLEUM PRODUCTS

COOKING 1078 - 541 8 - single fuel 549 - 297 8 - mixed (gas + electricity) 529 - 244 - HOT WATER 2123 . 248 I 175 I 44 HEATING 12528 3174 1346 950 - centralised heating 2669 1333 88 14 - independent heating 9552 1841 925 233 - other 306 - 333 703 2.2 Installation of Combustion Appliances

Installation of gas appliances in the home is governed by standards [l], which, among other prescriptions, lay down the ventilation requirements needed for that environment to be safe and healthy. Appliances with a direct external and open combustion chamber (Type B models) take, in the combustion, air from the interior environment and, if correctly installed, do not modify the indoor air quality. Appliances with a direct external flue gas and a close combustion chamber (Type C models), which take air directly from outdoors, have no effect on indoor air quality. Only stoves with no direct exterior flue gas can affect indoor air quality. Stoves must be installed in places where there are ventilation openings of a suitable size for the heat output and these openings must always discharge the combustion products via a suitable hood connected to a , flue pipes or directly to the external environment (FIG. 1). Filter hoods which are not connected to a flue system venting to the outside are not deemed suitable for the venting of combustion products. In cases where it is not possible to use a hood an electric may be used, if installed on an exterior window or wall and operating at the same time as the stove. Important prescriptions were introduced in Presidential Decree No. 21 8, [2] which established safety requirements for gas appliances realised before the 13.03.90. Presidential Decree procedures [3] introduce the concepts of ventilation (air required for combustion, meaning openings or holes to the exterior) and ventilation (air change required both for disposal of combustion products and to avoid a build-up of unburnt gas). In the room where the stove is installed the ventilation holes do not have to be made if the volume of the room is greater than 20 m3 and if it is equipped with a flue venting system, hood (expulsion not recirculation) or electric fan ventilation system (sucking) or a ventilation opening larger than 100 cmz located high up in the room. All these requirements ensure correct evacuation of combustion products and maintenance of indoor air quality.

FIG. 1: EXAMPLES OF GAS STOVES INSTALLATION

3. RESEARCH ON INDOOR AIR QUALITY

Snam, in co-operation with Italgas, Enitecnologie and Polytechnic University of Turin has carried out a three-year theoretical and practical research, the scope of which has been to evaluate the influence of the utilisation of natural gas combustion appliances on indoor air quality. Snam is the company which heads the Eni sector in charge of the supply, transmission, primary distribution and sale of natural gas in Italy. ltalgas is also an Eni company and is one of Europe's largest distributors of natural gas. Enitecnologie is the Eni group's industrial basic research company. The Energetic Department of Engineering Faculty of the Polytechnic University of Turin has been working on these issues since many years. It should be noted that there are no specific limits or regulations governing air quality in indoor environments. There are, however, recommended general levels suggested by certain bodies, including the World Health Organisation WHO) [4], or limits laid down by decrees which generally refer to the air quality of air outdoors, such as D.P.C.M. 28/3/1983 [5],Ministerial Decree D.M. 25- 11-94 [6] and Council European Directive 1999/30/CE [7]. There are also specific limits for working environments, which usually set thresholds which relate to continuous exposure as 8 hours (TLV- TWA) or acute exposure as 15 minutes (TLV-STEL); the body which sets these latter limits is the ACGIH (American Conference of Government Industrial Hygienists) [8]. TABLE 2 summarises carbon monoxide limits. TABLE 2: CONCENTRATION LIMITS FOR CARBON MONOXIDE

STANDARD CONCENTRATION LIMIT WHO 10 mg/rr? for 8 hour average concentration 30 mg/rr? for 1 hour average concentration 60 mgldfor 30 minute average concentration 100 mglrr? for 15 minute average concentration D.P.C.M. 28/3/1983 10 mgld as average 8 hour concentration; 40 mg/d as average 1 hour concentration. D.M. 25-1 1-94 Attention level 15 mg/d (average 1 hour) or 10 mglrr? (average 8 hours); alarm level = 30 mglrr? (average 1 hour) ACGIH 55 mg/rr? for 8 hours and for 40 working hours per week (TLV-TWA) 440 mg/rr? for 15 minutes (TLV-STEL)

3.1 Measurement of Emissions

The appliances selected for the test were two stoves, an oven, a type B water heater and a type B . The emissions were measured in accordance with existing standards. TABLE 3 gives stoves emissions from different sources and the emissions from the two stoves used in the experiment.

TABLE. 3: EMISSIONS FROM GAS STOVES (glGJ)

I co ' . NOx I NO FUEL EXPERIMENTAL STATION [9] Interval 30+107 17+40 Average value 76 27

~~ ~ LABORATORY MEASUREMENTS [lo] Interval 13+320 1941 12+21 5+1 9 Average value 60 31 16 9 US LITERATURE [lli151 Interval 1Ot240 30~60 1040 5-4 8 Average value 55 40 20 10 STOVE 1 Interval 1747 28i33 12+16 6+10 Average value 27 31 15 8 STOVE 2 Interval 13+146 31~41 1346 9+19 Average value 77 35 15 13

(*) Results are for burners turned up to maximum The different values are seen to correspond closely; the differences which occur are due to the type and age of the appliance and to the conditions of use. 3.2 Tests

The tests were carried out at the ltalgas testing station at Venaria Reale (TO). The buildings were constructed to simulate single family dwellings. They were fitted out for comparative thermotechnical tests on the various systems and components used in and space heating. The kitchen, where the tests were conducted, has a floor surface area of around 14 rr? and a volume of around 38 m3. Combustion products are vented through a flue, whilst local ventilation is ensured by openings ventilation of the type and size laid down in the standards and which can be vaned to suit the needs of the test. (FIG. 2).

FIG. 2: PLAN OF ITALGAS TEST BUILDINGS

I U I

The tests examined air changes rate and the influence on indoor air quality f vented appliances and stoves fitted in different plant configurations. Air changes rate were measured using the 'tracer gas' technique based on inflow, monitoring and breakdown over time of a selected quantity of a gas with suitable characteristics (it must not be toxic, it must not be present in the atmosphere and must be easily mixed with air); sulphur hexafluoride (SF6) is normally used. As far as concern tests on gas stoves a number of different use profiles were selected on the basis of conservative assumptions. The first series of experiments consisted of tests in extreme conditions of use. These tests were made referring to safety, rather than indoor air quality, and involved using all four rings as well as the oven, producing temperatures of up to 50°C near the cooker and simulating a level of gas use for cooking which was even 6 times higher than the standard consumption of 100 m3. The second set of tests involved conditions of heavy use. The conditions, still with conservative assumptions, were as follows: 0 stove functioning with an annual consumption of gas of 150 m3, which is over 50% more than the average consumption for an Italian family; 0 stove profile use in continuous or throughout the whole day, with the gas lit for a period in the morning, another period at midday and a period in the evening; 0 maintenance of static conditions in the kitchen (for example doors and/or windows closed); 0 analysis of installations which did not conform to standards (without ventilation openings, without an appropriate chimney for flue gas evacuation, without hoods). 3.3 Results

Analysis and interpretation of results obtained in experimental and modelling activities highlighted a series of correlations between installation and gas appliance use versus safety and indoor air quality.

3.3.1 Air Change Rate

Tests to measure air changes rate N were carried out while the range top was working. FIG 3 shows the air changes while 2 rings were working, with ventilation opening with the hood connected to the flue. It may be noted that N increases during the period when the gas has just been lit, due to the increase in temperature under the hood which generates an increased draught in the flue. After the two rings have been turned off the number of air changes decreases and then levels off. This phenomenon, which was also seen in other tests, established that the effect of the ventilation openings cannot be associated with a preset air change value, since variations of up to 100% in air change were measured, depending on the heat input from the hob, quite apart from the conditions of installation.

FIG. 3: AIR CHANGE TREND

2.50

2.00

s 1.50

1 .oo

0.50

3.3.2 Tests on Appliance with Exhaust Flue Gas

Tests on a water heater (21 kW) were carried out varying the position and area of the ventilation opening, the permeability of the room and the cross-section of the flue. A total of 134 tests were carried out; 109 in the sealed chamber at ltalgas laboratory in Asti and 25 at Venaria experimental buildings. The tests in the experimental buildings showed that, when the appliance was correctly installed, the variation in the position and cross-section of the openings ventilation did not influence the CO concentration in the indoor environment. When the room was completely closed (without openings) no appreciable CO concentration was noted in the area, a sign that sufficient ventilation was provided by the permeability of the building (FIG. 4). With the cross-section of the flue gas reduced by 60% (dn 75 mm. instead of 120 mm) the CO remains at around 6 mg/m3. (FIG. 5).

The tests in the laboratory sealed chamber showed that, when the appliance was correctly installed, the reduction in the opening ventilation (up to 75%) does not influence the CO concentration in the environment. If, however, there are conditions which limit the draught (reduced flue section or use of extractor fans) then the opening ventilation should be in accordance with the standards. ' FIG. 4: CO CONCENTRATION - VENTILATION OPENING CLOSED, NORMAL FLUE (dn=120)

10

9

8 I

E

E5W z4 3

2

1

0 ~~000000000~000000 ""x-tz"$?zA------r?r??YWr: 0000 0 time (h) FIG. 5: CO CONCENTRATION - VENTILATION OPENING CLOSED, REDUCED FLUE (dn=75)

10

9

8 I

$6E

W25 s4 3

2

1

0 0 0 00 0 0 0 0020 g2 o! 9 F! 0020c! 222 2 $0M M time (h) 3.3.3 Tests on Gas Stoves

The tests on gas stoves (8 kW) also evaluate non-standard installations, such as lack of ventilation I opening, lack of flue to vent the combustion products or lack of hood or electric fan. Tests on gas stoves in conditions of extreme use (18 tests) showed that, as far as concern CO I concentration, under no conditions including those where standards were not complied with and those

I where 4 rings and the oven were on at the same time, there were no conditions of slightest danger. With regard to air quality, in the case where 2 rings were on, even the CO exposure limits recommended by the World Health Organisation (WHO) were never exceeded. The gas stoves heavy use tests (40 tests) showed that, under all conditions, including those where the standards were not complied with, the CO concentration recommended by the WHO was never exceeded. The results of some of the conditions analysed are shown in TABLE 4, whilst FIG. 6 shows typical concentration levels for CO over time measured in the kitchen compared with WHO recommended exposure limits. The first series of tests was carried out with 2 rings alight (3.5 kW) for 80 consecutive minutes. The second series of tests was carried out with the following cycle: 1 small ring was lit at breakfast time for 15 minutes., 1 medium-sized ring at lunch time for 60 minutes and 2 medium-sized rings for 42 minutes at dinner time.

TABLE 4: CO CONCENTRATION IN THE KITCHEN

19 I 7.9 1 , 3.9 .I 2.3 I ~~ 2 RINGS 80' - CIG open+flue 6.4 5.4 2.6 2 6.1 5.1 2.4 1.8 3.4 3.1 1.9 1.8

6 5.1 3.6 2.5

~~ ~ CYCLE - CIG open 5.3 4.5 . 2.8 1.9

3.3 2.4 ~ 1.8 1.4 3.4 2.9 1.6 1.3 CYCLE - CIG open+hood 3.3 2.8 1.3 1.1 r

RECOMMENDED VALUE - HO I I I 30 10 I CIG open = presence of ventilation opening (prescribed by CIG, Italian Gas Committee standardisation)

FIG. 6: CO CONCENTRATION

5

4

g3 a WE

1

0 0 2 4 6 8 10 12 14 16 18 20 22 time (h) It may be noted that the presence of ventilation opening reduces CO concentrations by around 20%. The effect of the flue alone or the flue coupled with the ventilation opening is greater than the effect of the ventilation opening alone (average reduction of 40%). The average reduction with the electric fan (35%) is lower than that obtained with the flue, whilst with the hood there is a 70-80% reduction. ..

Passive samplers were used to measure exposure to nitrogen dioxide in a kitchen with a gas cooker. The passive samplers are devices which generally consist of small containers which can "capture" the substance which is to be analysed. The sampler used to measure nitrogen dioxide comprises a small cylinder with two opposing surfaces: one allows diffusion and is transparent to gas molecules to be sampled, whilst the other is of the absorbent type. The molecules which diffuse in are captured by the active surface in different ways depending on the substance to be analysed. Nitrogen oxides are measured by chemical adsorption capturing the molecules and irreversibly trapping them through a chemical reaction which radically alters their nature (the nitrogen dioxide is chemically adsorbed by triethanolamine (TEA), in which form the nitrites and nitrates that can be easily quantified). The variability of average daily concentrations, measured under normal living conditions for an installation which complies with the standards, is below WHO recommended levels, as summarised in TABLE 5. The table also shows the background concentration measured outside the dwellings.

TABLE 5: NITROGEN DIOXIDE CONCENTRATION IN KITCHEN

1 CONCENTRATION 1 BACKGROUND I WHO RECOMMENDED LEVELS IN KITCHEN CONCENTRATION (average 24 hrs) (average 24 hrs)

NO2 27 + 39 pg/d 10 + 13 pg/d 200 pg/d (average concentration over 1 hour)

40+50 pg/d (average annual concentration)

The nitrogen dioxide concentrations measured by the passive samplers were checked using ' continuous monitoring (FIG. 7). Comparison of the results obtained enabled the accuracy degree of the sampling devices, which proved to be excellent, with an. average difference of 15%.

FIG. 6: NO2 CONCENTRATION

500

400

300

hW 0"z 200

100

0 0 2 4 6 8 10 12 14 16 18 20 22 time (h) 3.4 Chemical and Physical Changes to Nitrogen Dioxide

The nitrogen dioxide adsorption by materials commonly present in the home environment was investigated. Studies in the literature have shown that NOs is removed from the indoor air through reaction with different materials present in the home. This process significantly lowers the life of nitrogen dioxide in interior environments, with a consequent reduction in exposure for human beings. In order to measure this phenomenon a specially designed glass room was constructed in the laboratory, in which the decay of nitrogen dioxide was to be measured. The materials selected were: colored wallpaper, woollen carpeting, wood covered with formica, plaster and cotton. The experiments conducted demonstrated the existence of significant nitrogen dioxide removal phenomena by the materials selected, particularly high for cotton, plaster and carpet, with reductions of between 34% and 48%.

3.5 Simulation Models

The presence of many parameters which influence experimental evaluation of indoor air quality, some of which such as climatic factors cannot be controlled, the need to have suitable test conditions available for long periods and the cost of managing the tests, have encouraged investigation of the possibilities of representing the diffusion phenomenon of gaseous substances in confined spaces through suitable mathematical models. The models which can be used for description of the phenomenon may be grouped as: 0 CFD models (commercial calculation programs based on the principles of ); 0 zone models; concentrated parameter models.

CFD (Computational Fluid Dynamics) methods are numerical methods based, in practical terms, on calculation programs which are available on the market and are used on very powerful computers. They allow the problem of pollutant diffusion in confined spaces to be solved with very precise spatial definition. At operational level the volume, for example the kitchen volume, is subdivided into basic cells with chemical, physical and geometrical characteristics which are known and held to be constant. The precision of the model depends on the number of cells considered. The differential equations which describe the phenomenon are resolved numerically by assigning finite values in a given interval to the physical values measured. Models of this sort currently available on the market are FLUENT (suitable for study of diffusion in a confined space) and COME (suitable for study of flows between different environments). Where practical application is concerned, however, there are considerable obstacles, which may be identified as: 0 availability of sufficient computing power; 0 considerable machine time required for resolution; difficulty on knowing and/or representing surrounding conditions exactly. The costs of applying CFD models suggest that they are suitable for limited use for a few specific survey situations rather than for routine evaluation; comparison of experimental data from some tests carried out at Venaria building and the result supplied by the FLUENT gives a 30% error.

The uzones" model allows solution of problems where a single room can be divided into clearly distinct zones. The kitchen is a practical example where it's possible to distinguish between the volume above and below the level of the cooker hob. The method also allows solution of problems where different confined spaces have easily identifiable characteristics. A practical example is the definition of air quality, or the level of pollution present in different rooms in a flat. In the mathematical model the zones (rooms) become nodes in the model, whilst appropriate equations are used to describe the link between them, such as the flow of gaseous substances and the difference in pressure and temperature between the rooms in question.

Concentrated parameter models are the simplest means of mathematical representation and are based on the principle that the variations in physical size within the 'boundaries' under consideration are negligible or have no Influence on the solution to the problem; through solution of equations of conservation of mass they can give 'average values' for pollutant concentration in the room considered. This model (simplified) is applied by starting from the mass balance, from which it is found that the quantity of a given gas accumulated in a given volume in the unit of time is equivalent to the difference between the quantity entering the system and the quantity leaving that system; therefore this gives the quantity generated within the space analysed. In strictly mathematical terms, the equation which models the phenomenon, assuming for simplicity that the mixing of air is approximately ..

uniform (or supposing that, at a ,given moment, the concentration is equal in all points in the room), is as follows:

dC S -- -P.R.Co+--(R+K).C dt V

where the symbols represent: C = concentration of indoor pollutant (g/m3); R = number of air changeshour (Ihr); t = time(hrs); P = penetration of pollutant from outside (nondimensional); Co =concentration of pollutant in the external environment (g/m3); . S = hourly pollutant emission (ghr); V = volume of the room (m3); K = speed of pollutant removal processes different from air changes (llhr).

By comparing the experimental values with the simulated values from the simplified model it is seen that there is a good match, so much so that conclusions obtained from measured data are largely the same as those which would be drawn from use of simplified model only. Use of simplified models makes it possible to overcome some inevitable limitations due to the specific features of the tests and the condition of the systems analysed. FIG. 8, given here as an example, shows CO concentration over time taken from real data from the testing station and the corresponding simulated data.

FIG. 8: CO CONCENTRATION OVER TIME

7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 hours

3.6 Analysis of literature

A number of studies [16+21] conducted by organisations or companies involved in gas industry, public bodies or independent institutes and by gas companies in co-operation with public bodies or independent institutes were analysed and evaluated. . _-

The study carried out in the USA in 1995 by three gas and electricity distribution companies [I61 gives the methods and results of an experiment measuring CO and other pollutants in dwellings in California during the winter. The 300 dwellings analysed were selected in a statistically representative manner in order to evaluate the influence of building characteristics, geographical location, weather conditions, ventilation, type of combustion appliance and the habits of the occupants on indoor air quality. The information gained was collected by means of questionnaires. For each dwelling sampling was carried out over a 48 hour period by continuous CO monitoring with electrochemical sensors and passive sampling for other pollutants, including nitrogen dioxide and volatile organic compounds. The results obtained are summarised in TABLE 6.

TABLE 6: RESULTS OF BIBLIOGRAPHICALANALYSIS [I61

MEASURED NO. CASES AVERAGE CONCENTRATION INDOOR OUTDOOR CARBON MONOXIDE (ppm) 277 1.6 1 MAX CONCENTRATION 8 hours (ppm) 277 2.9 2 MAX. CONCENTRATION 1 hour (ppm) 277 4.5 3.8 NITROGEN DIOXIDE (ppb) 21 1 25 23 AIR CHANGE (lhr) 287 0.57 -

It was found that: 0 internal CO concentration is closely related to the external concentration; 0 there are no significant differences in CO concentrations in dwellings with electric cookers and those with gas cookers without a pilot light; 0 in 13 dwellings out of 293 there were CO concentrations over the limit of 9 ppm for 8 hours, but for 8 of these 13 dwellings the external concentration was already over the permitted limit.

The 1993 English study carried out by the University of Bristol in co-operation with British Gas, [17] measured NOz levels in 921 dwellings, where there were children, over a two-week period in March 1993. These were selected in a statistically representative manner. The children were aged between 3 and 9 months. Passive samplers were used, installed in the breathing zone of each house. For around half the dwellings external exposure was also measured. A questionnaire on building characteristics, ventilation and type of combustion appliance was supplied to each occupier, including a list of symptoms relating to the child's health during the observation period. . NO2 concentration measured in the bedroom was from 0.6 + 86 ppb, with an arithmetical mean of 8.9 ppb; outdoor NO2 concentration was 1.7 + 46 ppb, with an arithmetical mean of 13.3 ppb. The environmental factors influencing NO2 concentration are traffic, cigarette smoke, ventilation of rooms and use of gas cookers. The final analysis showed that there is no statistically significant relationship between health symptoms and the level of NO2 in the house, including the absence of any association with use of gas cookers. The only associatiqns which emerged as causes of respiratory symptoms were the presence of damp and moulds.

The study carried out in Italy by the Milan University Institute of Health in co-operation with the University of Trento and the Multizone Health and Prevention Councils for Milan and Monza, [I81 gives the results of an experiment conducted in Monza area in 1995-96, with the aim of measuring exposure to CO of 75 patients affected with heart disease. Internal, external and personal passive samplers were used, capable of showing the cumulative concentration over 24 hours. Information on the characteristics of the dwellings and the people's habits was collected by means of a questionnaire. The results obtained are summarised in TABLE 7. TABLE 7: RESULTS OF BlBLlOGRAPHlCALANALYSIS [I81

ENVIRONMENT or APPLIANCE

ACCUMULATED EXTERNAL CONCENTRATION ACCUMULATED INTERNAL CONCENTRATION ACCUMULATED PERSONAL CONCENTRATION 36.1

ACCUMULATED EXTERNAL CONCENTRATION - FLATS NEXT TO ROAD 27 25.8 - FLATS NEXT TO ROAD BELOW 3RDFLOOR 42 - FLATS NEXT TO ROAD ABOVE 3RDFLOOR 14 - FLATS ON INTERNAL COURTYARD 48 14.7 ~~ DIFFERENCE BEMlEEN ACCUMULATED CONCENTRATION (INTERNAL- EXTERNAL): -WINDOWS OPEN FOR OVER 2 hrs. (") 34 4.7 - WINDOWS OPEN FOR UNDER 2 hrs. (") 41 7.1 - NON-SMOKERS (") 34 5.2 - SMOKERS PRESENT (") 12 13.8 - PASSIVE SMOKERS (**) 29 14.4 - HEATING (") 75 4-9 - GAS COOKER (") 75 not measurable

(*) = difference between internal and external contribution (**) = difference between personal end external Contribution It was found that the cumulative concentration measured with personal samplers is higher than the internal contribution, which in its turn is higher than the external contribution. The external CO contribution caused by traffic is substantial and is retated to the floor on which the dwelling is situated and the exposure of the windows. Exposure to CO is influenced by the way the windows are opened, by use of heating appliances and by the presence of smokers. There is no evidence for any influence from the use of a gas cooker. The study confirms that the CO values measured indicate the exposure level is low or moderate and that it does not appear to constitute a health risk.

4. CONCLUSIONS

Indoor air quality depends on many factors: combustion appliances are one of many sources of pollutant emissions which are found inside dwellings. Gas appliances and in particular cooker installations are regulated by UNI-CIG standards, which among other prescriptions establish the ventilation requirements which guarantee the safety and health of the environments through sufficient air changes, thereby avoiding the accumulation of pollutants which are also emitted by other internal sources. The tests performed, along with the development and application of mathematical models which have supplied results that closely match those from testing, have firstly supplied valid theoretical and experimental support for standardisation work. They have also established, confirming the literature research data from measurement programmes in dwellings, that use of gas appliances, including gas stoves with no external flue gas for discharge of combustion products has little influence on indoor air quality and does not affect human health. REFERENCES

UNI-CIG Standard 7129 ‘Impianti a gas per us0 domestico alimentati da rete di distnbuzione - Progettazione, installazione e manutenzione” Presidential Decree DPR 13 maggio 1998 n. 218 “Regolamento recante disposizioni in materia di sicurezza degli impianti alimentati con gas combustibile per us0 domestico” Official Gazette 9 July 1998 UNI Standard 10738 “Impianti alimentati a gas combustibile per us0 domestico preesistenti alla data del 13 marzo 1990 - Linee guida per la verifica delle caratteristiche funzionali” “Air Quality Giudelines for Europe“ World Health Organization (WHO-OMS) Reg. Pub. Geneva 1996 Decree of the President and Council of Ministers D.P.C.M. 28/3/1983 ”Limiti massimi di accettabilita delle concentrazioni e di esposizione relativi ad inquinanti dell’aria nell’ambiente esterno“ Ministerial Decree D.M. 25-11-94 ‘Rggiornamento delle norrne tecniche in materia di limiti di concentrazione e di livelli di attenzione e di allarrne per gli inquinanti atmosferici nelle aree urbane e disposizioni per la misura di alcuni inquinanti” G. U. n. 290 del 13.12 94 Council European Directive 1999/30/CE concerning environment air quality limit values for sulphur dioxide, nitrogen dioxide, nitrogen oxide, particulate and lead, 29 June 1999, L 163/41. Limits set by ACGIH (American Conference of Government and Industrial Hygienists) for working environments. Stazione Sperimentale per i Combustibili “Emissioni inquinanti da cucine a gas”, Report B30780, S. Donato Mil.se 20 december 1993 [lo] “Deterrninazione, in laboratorio, delle emissioni di ossidi di azoto da generatori di calore ad us0 civile“ ltalgas Testing and Research Centre, Asti, June 1989 [lI] “Field Measurements of NO2 gas range top burners emission rates” D.J. Moschandreas, S.M. Relwani, Proceedings of Indoor Air 87, Berlin West August 1987. 1121 “Control of NOx emissions from residential gas appliances” M.J. Murphy, A.A. Putnam, GRI REPORT 8510132 [13] “Characterization of emission rates from indoor combustion sources“ D.J. Moschandreas, S.M. Relwani, ed altri, GRI REPORT 85/0075 [14] “Emissions from residential fired appliances“ J.T. Cole! T.S. Zawacki, GRI REPORT 84/0164. [15] “Indoor Air Pollution due to emissions from unvented gas fired ‘space heaters” J G.W. Traynor, J.R. Girman, M.G. Apte, J.F. Dillworth, P. White , APCA March 1985, Vol. 35, 231:237. [I61 I.H. Billick, ed al. ”California residential indoor air quality study: an overview”, International Gas Research Conference, Cannes, France, 1995 Pag. 350-359 [17] P.J. Finch ed al. “A survey of residential nitrogen dioxide levels in Bristol, UK“ International Gas Research Conference, Cannes, France, 1995 Pag. 366-374 [18] “Extrenal carbon monoxide exposure levels of subjects“ studio lstituto d’igiene di Milano - Air Pollution V pag. 1005-1014, Bologna 1997 [19] “Estimation of pollutant emission from domestic combustion sources: their influence on indoor air quality”, Cavicchioli, Negri ed al. ClSE ENEL CRTN (MI) (1992) - International Conference on I “Energy and Environment towards the year 2000” Capri 3-5 Giugno 1992 [20] “Risultati di un monitoraggio della qualita dell’aria in 50 abitazioni milanesi“ Gallo F. Domino srl ARIA 94 Conference [21] W. Spicer ed al. ”Persistence and fate of natural gas appliance emissions” International Gas Research Conference, Cannes, France, 1995 Pag. 395-404