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downdraughts due to turbulence downwind of the building should be Height of building + 0.6 x uncorrected chimney height d) Clean Air Act, 3rd Memorandum on Chimney Heights. The 3rd Memorandum methodology is less complex. The pollutant level of hydrogen chloride is converted to a `sulphur dioxide equivalent' as above, but this is then multiplied by a 'district factor' which corrects for background levels of pollutants in different types of area. The uncorrected stack height is calculated directly from the pollution loading. Following this, the final chimney height is calculated by adding 0.6 x the uncorrected chimney height to the maximum height of the building. e) Secretary of State's Guidance (PG5/3(91) The Secretary of State guidance lays down that the minimum chimney or process vent height should be three metres above the roof ridge height of any building within a distance of five times the uncorrected chimney height, and in no circumstances should be less than eight metres above ground level. It is relevant to point out that the standard calculations specified by the methodologies outlined above apply to an incinerator sited on land which is essentially flat, and which does not have significant obstructions to reasonably smooth air flows across the site. In the Public Inquiry into the proposed Whiddon Down BSE Incinerator (Applicant Mr R Toms; April 1992) , it was held that relevant topographic features of the site should be taken into account in the calculation of the chimney height. The possibility that the siting of the crematorium may be such that downdraughts may develop behind the building(s) near the chimney therefore needs to be taken into account. It is generally agreed that the air flowing over a building is disturbed up to a height of 1.5 times above the height of the building. Moreover, disturbance of the air flow may extend to a distance of up to five times the height of the obstruction downwind of it (see note at the head of this section, above) . The presence of large trees on the upwind side of the site indicates that they are liable to cause disturbance of the air flow across the site for a very substantial distance downwind, and may therefore interfere with the idealised smooth air flow over the proposed buildings. The complex calculations required to determine the eventual dimensions of the chimney of the proposed facility appear not to have been provided in the Planning Application, and should be regarded as a significant and important defect in the application. This factor is discussed in the following sections. Any claim that the emission temperature of the Crematorium effluent will be so high that it would 'punch its way' up into the atmosphere should be viewed with considerable scepticism. Any observation of even the large municipal incinerator at Marsh Barton, Exeter, will show that such an idealised situation only occurs during periods of almost total calm-n o t a situation which is common on the verges of Dartmoor. For all normal operating purposes, it will be the horizontal mixing pattern that will determine the dispersion of the effluent plume = as I shall attempt to establish below, the topographical characteristics of this specific site suggest that there will be substantial interference with the idealised theoretical pattern of plume dispersal, which will be very different to the gentle upward dispersal pattern envisaged by the Proponents of the Application.