Emissions to the atmosphere I

In our modern society there are a variety of sources of undesirable imissions to the atmosphere. The largest emissions of airborne pollutants come from the combustion of fossil fuels (both for heating and the production of energy) and from the transport sector (including cars, buses, shipping, trains and planes). As an example it can be mentioned that of 56 Mton carbon dioxide (CO2) that was emitted to the atmosphere in Sweden, 1993, more than 22 Mton came from industry (combustion of fossil fuels) while close to 25 Mton came from the transport sector. Only 8 Mton (i.e., <15%) came from other sources such as households, the service sector and the retail sector. Corresponding total emission levels of other environmentally important gases were: carbon monoxide (CO): 1.1 Mton, nitrogen oxides (NOx): 0.4 Mton, and sulfur dioxide (SO2): 0.1 Mton. Only a negligible amount of these species (<1%) came from sources other than industry and the transport sector.

The sources mentioned above are all regulated in terms of acceptable emission levels. In Sweden the combustion of fossil fuels, for example, may not give rise to higher particulate emissions than 0.5 g/kg fuel burnt in a furnace that produces more than 10 MW. In this context the term 'particulate' refers to an undefined mixture of soot, tar, unburned hydrocarbons and inorganic material that has not been removed in the exhaust treatment process. The same furnace may by law only emit 1-8 g NOx per kg solid fuel.

One source of pollutants, that has until now been spared scrutiny in terms of its environmental impact, is fires. According to information from the Swedish Fire Protection Association and the Swedish National Rescue Services Board between 30-40 000 fires are reported in Sweden each year. Approximately 30 % of all fires are domestic while the remainder are commercial, including industrial and rural sources. Amongst domestic fires approximately 200-300 occur where the premises are fully burnt while the corresponding number for industrial fires is about 10-20. In the latter case buildings with an area of several thousand square meters may be involved. Emissions from such fires can be of local significance while having an unknown national or global impact. As a comparison to the emission levels imposed on industry it should be noted that wood fires produce more than 10 g particulate matter per kg fuel burnt even when the fire has a ready supply of oxygen. The corresponding figure for plastic can be up towards 200 g/kg. In other words fires can give rise to emissions of particulate matter of the order of 20-400 times the acceptable level for a controlled combustion source. In cases where the fire has poor access to oxygen or the fire is merely smouldering particulate emissions are even higher.

A full study of pollutant emissions from fires is desirable not only as a means for establishing the importance of fires as pollutant sources relative to other sources but also to provide a sound basis for the determination of the most effective way to fight fires based, at least partially, on their potential environmental impact. This question should be considered on several levels, i.e., both in terms of working environment for firemen, living environment for civilians close to large fires and in terms of long-term environmental effects. These questions are interrelated but not entirely overlapping and the importance of the various emissions may be different in each case. As an example, the emission of CO from fires is of great importance in the immediate vicinity of the fire (as very high local concentrations of CO can accumulate) and it is believed that CO inhalation is one of the major causes of death in fires. The amount of CO emitted from fires is, however, minor compared to other sources of CO and thus fires are of minor importance for national CO levels.

In this project a first collation of the level of emission, of a variety of toxic species when various materials burn, has been made. The most commonly occurring types of material in housing, apartments, schools etc. have been taken into account. The total amount of emission from fires has then been determined based on fire statistics from the Swedish Fire Protection Association, the National Rescue Services Board and Insurance Federation. The levels of emission that have been calculated are, of course, uncertain but they do give an indication of the magnitude of fire emission and provide the basis for a meaningful discussion of the importance of fire emissions relative to other sources.

Details of this project can be found in SP report 1995:70 (in Swedish) or in Fire Technology, Volume 34 (3) 1998.

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Margaret Simonson McNamee

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SP Technical Research Institute of Sweden, Box 857, SE-501 15 Borås Phone +46 10-516 50 00, E-mail info@sp.se