Effect Of Diesel Fumes From Buses “Negligible”

Press, Volume XCVIII, Issue 28922, 16 June 1959, Page 18

Effect Of Diesel Fumes From Buses “Negligible”

“Exhaust fumes from petrol vehicles are much more poisonous than those emitted from diesel buses,” said the general manager of the Christchurch Transport Board (Mr J. F. Fardell). He was replying to the following letter about fumes from buses, to the editor of “The Press”:—

Sir,—The time seems opportune for action on another serious cause of air pollution—that Of motor-vehicle exhaust fumes. The black fumes which one notices belching from under diesel buses, besides being much more poisonous, are exhausted in greater quantity from diesel than from petrol motors. As more diesel buses are taking the place of trams for our cities, it is high time the authorities took what steps are possible to lessen diesel exhaust pollution of the air. A simple means of minimising the breathing of these fumes by most people would be to lead the exhaust outlets of diesel buses and trucks operating in cities to their roof level. From here, the warm fumes would continue to rise and dissipate.—Yours etc., SEMI-GASSED. May 15, 1959

“In fact, experiments carried out by both medical and motor industries research associations in Great Britain and America have found that the constituent parts of exhaust gases which are toxic are present in much greater quantities in the exhaust fumes from the petrol-engined vehicle, and it is authoritatively stated by the medical experts that today they are much more concerned with the toxic effects of carbon monoxide than the effects of benzpyrene in the exhaust gases,” Mr Fardell said.

Output of Gases Volume 24, August, 1955 of the “Industrial. Medical and Surgery Journal” in the United States showed that above idling speed the ordinary carbon monoxide output of diesel engines was less than one part in 10,000 of exhaust gas, whereas petrol engines normally produced carbon monoxide at a rate of about 1500 parts in 10,000 of exhaust gas, he said. “This means that petrol engine exhausts pollute the air with carbon monoxide at a rate of 1500 times greater than the diese] engine.” There were 53,366 registered motor-vehicles in metropolitan Christchurch at December, 1957, compared with 234 diesel vehicles —of which the board owned 155, said Mr Fardell. “The ratio of motor-vehicles to

buses is 228:1, and from this it will be seen that the diesel buses' contribution to carbon monoxide pollution is negligible. The toxic effects from petrol-engine vehicles can be high and can reach proportions which might be considered injurious to persons prone to pulmonary and bronchial disorders.

Position of Pipe “Experiments with exhaust pipe at roof level position both from wind-tunnel and operations tests have shown that terminating the exhaust pipes of diesel buses above the roof level has disadvantages which outweigh any benefits.” said Mr Fardell. “The air stream caused by movement of the vehicle frequently draws the exhaust gases inside the vehicles, especially in conditions of dense and slow-moving traffic. “The constituents of the diesel exhaust gases, being heavier than air, would still tend to ground level with the roof position type of exhaust. Condensation of the exhaust gases in the outlet pipe—a phenomenon which is always present in some measure—would tend to be accentuated if the exhaust pipes were lengthened to achieve this elevated point of ejection. It has been found that the most satisfactory position for the exhaust pipe to be fitted is brought out to the rear offside of the vehicle, as is the case in the board’s buses.”

Every effort was being made to prevent the emission of black smoke from exhausts, and each time it was seen, vehicles had their injection systems adjusted to alleviate this condition, Mr Fardell said.