View report page

66
and whereas complaints have been dealt with in respect to objectionable
smells emanating from the fresh air inlet shafts from the
larger traps, no similar complaints have been received in respect to
air inlets in connection with 4-in. traps.
In respect to the retention or abolition of the trap, from our
general experience we are strongly of opinion that, provided the
interceptor is selected with reasonable care as regards its shape and
size, and fixed with, say, a 2-in. seal, the gradient of the drain being
sufficient, it will work well, and that the likelihood of a blockage is
remote. When a blockage does occur, a considerable amount of
sewage may collect in the manhole before the stoppage is discovered,
and for this reason we consider that the trap should not have direct
connection with the manhole : i.e., a manhole should be constructed
over the trap to provide means of access only, and in order to
examine the interior of such trap it would be necessary to remove
certain water-tight stoppers provided for the purpose.
In the event of the intercepting trap being abolished we do not
consider that the additional ventilation of the sewers would render
the air in them as innocuous as the air in house drains, which are
disconnected from the sewers, and abolition of the trap would certainly
not be justifiable in order to prevent the occurrence of a very
small percentage of blockages, many of which are caused through
bad workmanship. Moreover, the removal of the interceptor would,
in our opinion, be attended with grave risk of sewer gas gaining
access to the inside of dwelling houses or their immediate surroundings,
and, consequently prove a menace to health. It may be said
that if the drains were made perfectly water-tight it would not be
possible for sewer gas to escape from them. But experience proves
that drains which are constructed with glazed stoneware pipes embedded
in concrete cannot be relied upon to remain air or watertight
(even for short periods in many instances) owing to movements
of the soil and to the expansion of the cement used for jointing the
pipes. (See Annual Reports for Finchley for the years 1902, pages
59 and 60, and 1906, pages 69 and 70.) This difficulty may be largely
oVercome by constructing drains with heavy cast-iron coated pipes
and the soil pipes and ventilating shafts with heavy cast-iron coated
pipes or solid drawn lead, but, even in the event of these precautions
being taken, there would always be the risk of wr.c. traps and gullies
being broken, or of such traps becoming unsealed from various causes.