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Report of the Medical Officer of Health.
153
Trent) are stated to have no arrangements for ventilation of sewers
whatever and that seven have no surface ventilators and that they
experience no difficulty. On the other hand it has been shewn
the number of gratings complained of in the Borough in one year
was 123, that there are 1,581 such gratings open, a percentage of
only about eight per cent., and although the smell may be disagreeable,
it is not necessarily dangerous and is as far from the
houses as possible, and is soon diluted by fresh air. That it is
necessary to provide ample fresh air in the sewers themselves
and that this cannot be efficiently done by tall shafts only. That
it is necessary to allow for the air expelled by sudden influxes of
sewage and storm water into sewers which might in the absence
of surface gratings, be forced through the interceptor traps of
house drains and so give rise to greater nuisance than at present.
That sufficient tall shafts to equal the area of the road gratings
would mean a very large addition to the present number and that
they would be less efficient on account of the height of the
column of air, and further, cases have been mentioned of nuisance
from these tall shafts in certain conditions of the atmosphere. It
is impossible to compare the conditions of London with those in
other towns.
The Committee therefore makes the following recommendations:—
That ventilating columns or shafts be placed—
(a) at the dead ends of sewers,
(b) elsewhere where found necessary,
arranged to rise from the crown of the sewer by a conical or
bell-shaped enlargement.
That it is advisable to have, in some cases, these shafts proceeding
from the house drain between the interceptor and the
sewer, the sewer flap trap being omitted.
That in case of combined drainage the interceptor on the
main drain should be omitted and a ventilating shaft or column
fixed at the summit of the drain.
That wherever possible dead ends of sewers should be made
to communicate with other sewers in the neighbourhood.