Air pollution in diesel bus garages.

Abstract

Motor vehicles emit exhaust products which are potentially noxious to a degree which depends on their ultimate concentration in the ambient air. Fitton (1957) has discussed some aspects of air pollution by road transport and has compared the emission of pollutants from petrol and diesel engines ; well maintained and properly operated diesel engines emit much less carbon monoxide and unburnt fuel than petrol engines. Diesel engines are, however, liable to emit black smoke; in well maintained vehicles this may be limited to a small puff on acceleration, but in others dense black clouds may be emitted, particularly at full load. Kotin, Falk, and Thomas (1955) have reported the presence of carcinogenic hydrocarbons in smoke from an inefficiently operating diesel engine. Other poten tially harmful exhaust products include oxides of nitrogen and aldehydes; these are emitted in similar concentrations by both petrol and diesel engines. Though much analytical work on the composition of motor exhausts has been published, relatively little is known about the concentrations of pollu tants (other than carbon monoxide) which traffic may produce in the air men breathe; without this information it is difficult to make any reasonable assessment of possible hazards to health. The work reported in this paper is the first part of a larger attempt to fill this deficiency in our knowledge of air pollution. We have studied air pollution in diesel bus garages where there are clearly defined groups of men who are regularly exposed to relatively high concentrations of exhaust products. In some cases the same men have been employed on similar work over long periods and sickness records are available. Raffle (1957) has studied the deaths, retirements due to ill health, and transfers to alternative work due to lung cancer amongst various groups of London Transport employees. Results of pollution measurements in any garage are only applicable to the particular types of vehicle involved and to the running conditions obtaining within it, but they are of direct relevance to the health of the men em ployed there. The m asurements reported here were made in two Lond Transport garages, and form part of a larger programme of work in which individual bu es are also being tested under various running conditions. An interim report on smoke in one of the garages has already been published (Commins, Wa l r, and Lawther, 1956). Pollution in London stree s is also being measured and further work is planned to study pollution in tunnels and in garages housing petrol-engined vehicles. London Transport's central fleet is made up of two main types of diesel bus, designated RT and RTL; for reasons of engineering maintenance they a segregated in different garages. Both have 6-cylinder engines of 9*6 litres capacity. There are also many variations in the sizes and plans of garages. In consultation with London Transport two garages with relatively poor ventilation were select d for study. The first was Merton (Fig. 1) which houses nearly 200 buses the majority of which are RTs. It is situated in a residential and manu facturing area about seven miles to the south of C aring Cross. The second was Dalston (Fig. 2) where about 120 buses, mainly RTLs, are housed. This is in a densely populated area in north-east London. Merton garage was constructed in 1913 and Dalston in 1907. Both garages are ventilated only by natural draught. Most of the buses leave the garages in the early morning and some return for periods during the day. All finally return during the evening, when each bus is washed and re-fuelled before being parked. There are three sets of conditions which cause pollution. First, when the buses are started up from cold in the mor ing a lachrymatory mist is produced for short periods; the intensity and duration of this mist varies with the temperature of the engine and of the ambient air. Secondly, a few buses remain in the its for repairs during the day and smoke is some times emitted when the engines are tested, but pipes are provided to carry this away. Thirdly, high pollution is produced during the run-in in the evening; drivers leave their buses with the engine 232