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The most important difference is in the treatment of furnaces
emitting only small amounts of sulphur dioxide. In the 1963
Memorandum, the minimum chimney height indicated by Appendix
I is 40 feet, and even quite low rates of emission take the height
considerably above that level. Experience has shown that these
levels are unduly onerous having regard to the smallness of the
emission. Appendix I of "Chimney Heights" accordingly allows
for uncorrected chimney heights starting at 16 feet and makes no
provision for emissions of less than 3 lbs./hr. S02; a new Appendix
VI gives final chimney heights for small furnaces starting at 25 feet.
Like the earlier Memorandum, "Chimney Heights" is issued
without prejudice to the Ministers' consideration of any appeal
under section 10 (3) of the Act.
Joint Circular 52/67 and 23/67—Grit and Dust.—This
Circular issued on 1st August, 1967, refers to the publication "Grit
and Dust" on the reduction of air pollution and grit discharged
from boiler and furnace chimneys.
"Grit and Dust" supplements the Explanatory Memorandum on
the industrial provisions of the Clean Air Act, 1956. It is based
on the Report of a Working Party which the Clean Air Council
agreed should be set up in 1964 to consider ways and means of
measuring grit and dust emissions and to advise on appropriate
levels of emission in relation to furnaces burning fuel equivalent
to 100-50,000 pounds per hour of coal.
It contains general guidance on the reduction of grit and dust,
explains in detail a method of measuring emissions and gives
advice on its use, and recommends levels to which it should
normally be possible to reduce emissions. A wider range is covered
than the grit and dust provisions of the 1956 Act since sections
6 and 7 do not apply to furnaces burning less than one ton an hour
of solid fuel (other than pulverised fuel) or solid waste, and none
of the provisions applies to oil fuel furnaces. "Grit and Dust",
however, does not cover emissions from furnaces where the
material being heated contributes to the emission, as further investigation is necessary.
Local authorities, especially those in the black areas (Greater
London is one), are called on to review all sources of grit and
dust, and to take all practical steps to get the emissions reduced
to acceptable limits.
As regards the measurement of emissions, attention is drawn
to the following points :—
(a) Any defects in maintenance and use of the plant should
be eliminated beforehand.