The last improvement suggested to give a better system of sewer ventilation in the City is the erection of shafts at the sides of the buildings where possible. A resolution was passed last year by the City Commissioners of Sewers to erect these shafts where practicable. The effect of this alteration will be to remove the nuisance from the street and carry it to a higher level. If it is intended to work these shafts in conjunction with the open gratings, the effect will be that in some streets the whole of the gas from the sewers adjoining will be pouring out of one shaft. In the summer time its density will be increased by the friction in the shafts, and the high temperature of the atmosphere will cause a more rapid decomposition in the sewage.
In low buildings or warehouses there is nothing to prevent the poisons from the sewers from being conveyed down the chimneys into the buildings, and the employés taking a zymotic disease whilst engaged in their work and at night taking it to various parts of the suburbs.
It is better to let the gas escape at a low level, where it could be purified when it is a nuisance, and especially in the case of an epidemic, than discharge gas with a greater density at a higher level.
The General Board of Health in 1848 issued the following minutes of information with reference to sewers and house drains—
“Make proper provision for the ventilation of sewers and drains in such a manner that there may be a free current of air in them in the direction of the sewage flow.”
It was also recommended “that the stack pipes should be connected with the sewers without the intervention of traps, in order to assist the ventilation, and there should be no trap between the trap at the inlet and the sewer.”
This system was found far worse than the open gulleys or shoots in the City in 1830, as at Croydon (which was one of the first towns to carry out works of sewage under the General Board of Health) no sooner had the sewers been in use before an outbreak of fever took place.
Dr. Niell Arnott and Mr. T. Page, C.E., were appointed by the Home Secretary to report on the outbreak at Croydon, and Mr. Page in his report states—
“Whenever a water-closet even with the best form of siphon trap is introduced into a house, it will be well to provide an escape into the open air. When several soil-pans or sinks from the apartments of a large house are discharged into a common soil-pipe or vertical main, the main should be continued up to the roof and to the open air, and if practicable it should be carried near the chimney. Pipe sewers must also have ample ventilation provided at all available points. If the air is confined it is most dangerous when it breaks forth, which sooner or later it will do, such evils would have been avoided.”
It is quite evident by these remarks that the system of ventilating the City sewers in 1830 was more perfect than at Croydon, and had Mr. Page tested the sewers and sanitary fittings by the compression of gases in them, he would have found that the action of the water in the pipe prevented the gas from being confined.