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152
Report of the Medical Officer of Health.
2.—That the proper cleansing of the drains and traps requires
the provision of flushing cisterns of a larger capacity than
at present permitted and that in new buildings there should be
regulation as to the minimum internal diameter of the feed pipes
of the flushing cisterns at present in use, in accordance with the
head of water.
3.—That there is clear evidence to show that sewer air runs
along the crown of the sewer and that it does not follow any
constant direction, that it sometimes descends with the sewage
and sometimes ascends the sewers and will find exit by openings
at certain distances from its source, and particularly at the dead
ends and on the main lines of sewers.
4.—That the course of the sewer air and its retention in or
exit from a sewer depends, in the absence of artificial means of
ventilation, on the temperature and humidity of the outside air,
and the direction of the prevailing winds.
5.—That the proper ventilation of drains and the prevention
of nuisance arising in connection with it requires:—
(a) Sufficient fall of sewer in all cases where possible to
secure self cleansing.
(b) Sufficient flushings by water.
(c) Free admission of air to the sewers.
6.—That while it would undoubtedly improve the ventilation
of sewers if the interceptor trap on the house drains were removed.
it would at present be impossible, on account of the certain opposition
of the public, to adopt such a system. In case of combined
drainage the interceptor in the main drain should be omitted and
a ventilating shaft put at the summit of the drain.
7.—That it is necessary to ventilate not only the sewer, but
the branches opening into it between the interceptor trap and the
sewer.
With regard to the practical means to be taken to ventilate
sewers and at the same time to prevent a nuisance the Committee
has given much consideration to the question of closing all the
surface ventilators and constructing more tall shafts. In favour of
this policy is the fact of the complaints of nuisances—smells—
from these gratings, and that two towns (Bristol and Burton-on-