Accidents in sewers : report on the precautions necessary for the safety of persons entering sewers and sewage tanks.

  • Great Britain. Committee on Accidents in Sewers.
Date:
1934
Catalogue details

Licence: Public Domain Mark

Credit: Accidents in sewers : report on the precautions necessary for the safety of persons entering sewers and sewage tanks. Source: Wellcome Collection.

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    Ny ‘ Classes of Danger 6. Dangers which may be anticipated in sewers a sewage tanks fall naturally under two heads :— | (1) Flooding. (2) Gases. (a) asphyxiating gases. (5) poisonous gases. e . (c) inflammable gases. LO ne ee Flooding i= 13 a] i © { > RES EASES AE 7. The danger of injury to men working in a sewer Thode rush of sewage or water is likely to arise from (a) storms ; (b) ‘abnormal tide action in sewers under tidal influence or (c) the sudden releasing of large volumes of sewage. The occurrence of (a) and (5) cannot generally be anticipated and reliance must be placed on the alertness of the staff. As regards (c) such an occurrence could arise only from lack of co-ordination between the persons responsible for the discharge of sewage and the persons in charge of men working in the sewers. It is our view, and this has ‘been agreed generally by our witnesses, that it is highly desirable that bars or chains should be provided at all man-holes in sewers in which men can work so that they can be fixed across the sewer at the manhole below the point at which any man is working. Gases in Sewers and Sewage Tanks Gases in Sewers 8. The composition of the atmosphere in sewers normally varies very little irom that of the outside atmosphere. In certain circumstances, however, it is possible for the atmosphere in sewers to be considerably modified in composition either as a result of relative stagnation of the sewage due to structural defects in the sewers or by the wilful or accidental admission into the sewers of gases such as coal gas or of liquids which readily vaporise. 9. In sewers which are laid at a very flat gradient or which have been subject to subsidence it often happens that the sewage is comparatively stagnant and that the solid matters in the sewage settle out and remain lodged in one position. These solids, if they remain long enough, undergo fermentation and absorb oxygen from the air in the sewer. If the air is comparatively stagnant its composition is quickly altered both by the emission of fermentation gases and by the absorption of the oxygen. The fermentation or digestion of sewage solids gives rise in the early stages to very objectionable odours and an acid condition of the solids. The gases evolved at this stage are mainly carbon-dioxide, hydrogen, sulphuretted hydrogen and some methane. As ithe fermentation proceeds the solids become alkaline in character due to the predominance of other organisms and the gases evolved consist very largely of a mixture of methane (60 per cent. to 80 per cent.) and carbon-dioxide (15 per cent. to 20 per cent.). 10. It will be obvious that if the air in the sewer is comparatively stagnant these evolved gases will coliect and gradually displace the air with the result that the sewer atmosphere will become ‘rrespirable owing to the reduction of its oxygen content, and even explosive owing to the presence of the inflammable gas methane. Sulphuretted hydrogen is also inflammable but is hardly likely to occur in sufficient quantities to give an explosive