Service Delivery 4

1. Service Delivery 4 Sewers

2. Learning Outcomes At the end of the session students will be able to: • Understand the practical implications of access to sewers through manholes, shafts and chambers • Be aware of ventilation considerations and the danger from sewer gas • Understand the method of effecting rescues from sewers.

3. Sewerage system • Today's underground systems have developed since the Victorian period and form a complex underground network of pipes and chambers • By the very nature of the waste products being transported, access and rescue require a certain amount of specialist knowledge.

4. Sewerage system • In most cities and large towns a vast complicated network of sewers has been established for the discharge underground of domestic sewage, trade wastes and rain water.

5. Sewerage system • Sewers form an intricate arrangement of pipes ranging in size from about 150mm diameter to as large as 7 metres in diameter • Local sewers are small in diameter and they discharge into the larger main sewer system which in turn carries the waste materials eventually to one of the purification works for ultimate disposal.

6. Sewerage system • The system of sewage pipes is arranged in such a way that should work of any kind be required in a section, flow may be diverted by the use of sluice gates and penstocks to alternative routes.

7. Manholes • To enable repairs and maintenance to be easily carried out, and to facilitate ventilation, sewage systems are provided with vertical access shafts • Engineers may gain access from street or footpath level from these • It is from these manholes that any sewer rescue must be carried out.

8. Limited access • Manholes and shafts are designed primarily for use by workers carrying only a few tools • The firefighter wearing breathing apparatus will naturally experience considerable restriction to their movements when ascending or descending.

9. Sewer gas • The collapse of workers in sewers is usually caused by the presence of sewer gas • This gas is a mixture of sulphuretted hydrogen and methane, both of which are toxic and flammable • The mixture may burn explosively when mixed in the correct proportions with air.

10. Sewer gas • These gases are formed during the decomposition of sludge lying on the bottom of slow moving or stagnant sewers, e.g. in level section or upstream of blockages • The gases form a honeycomb of bubbles in the sludge where they are trapped.

11. Sewer gas • When the sludge is disturbed or waded through the gas is released and bubbles up to the surface into the air space above. Sludge Gas Honeycomb

12. Benchings • The benchings in sewer chambers slope towards the sewer invert to facilitate drainage • When wet these benchings present a hazard to the firefighter, especially when wearing rubber boots.

13. In many sewers a safety chain or guard bar is placed across the sewer immediately downstream from the manhole to act as a handgrip for personnel working upstream from it.

14. Where the invert of a sewer is more than about 6m below the surface it is normal for the ladder climb to be interrupted by a platform placed halfway.

15. Underwater spurs • A danger frequently encountered is the underwater spur at the junction of two sewer pipes • The spur projects for some distance and may cause the rescuers to stumble or fall.

16. Underwater spurs.

17. Underwater hazards • Bars suspended from the roof of the sewer and/or safety chains are frequently used to indicate underwater spurs and other hazards, such as a sudden drop in the sewer level • This can be as much as 1 or 2 metres in a large sewer.

18. Sewer rescues • Speed is essential • BA should be donned en-route • Check with Brigade Control that an ambulance has been mobilised.

19. Surface contact • When workers are employed in a sewer a surface contact is invariably left above ground to keep in touch with the persons working below • The surface person should be contacted to find out exactly where the workers below are located.

20. Light and ventilation • As soon as the probable position of the people to be rescued is established, manhole covers either side should be removed for light/ventilation and ease of rescue • Two firefighters in breathing apparatus should make their way down the shaft and proceed along the sewer.

21. Breathing apparatus • A third firefighter should descend the shaft to the foot of the ladder while a fourth remains above ground so that contact may be maintained between rescuers and surface at all times • BA must be worn by all four firefighters.

22. Raising to street level • The casualty should be moved to the nearest available shaft • The best method of raising the casualty to ground level is using the body harness which all sewer workers wear and use of the confined space equipment.

23. Sudden flooding • During any rescue attempt that entails entering a sewer, the rescuer(s) must always be fully alert to the possibility of sudden flooding.

24. Changes in weather.

25. Changes in weather Among the typical warnings for sudden flooding are; • Movement of air through sewer • Rising level of effluent • Increase in speed of flow • Increase in noise.

26. Bacterial infection • Weil's disease is found in sewers and originates from the urine of rats • In the early stage Weil's disease is often mistaken for influenza, pneumonia, tonsillitis or some other common ailment.

27. Hygiene precautions • After working in contact with sewerage hands and forearms must be washed with soap and warm water • Clothing, boots and equipment, which are contaminated with sewage, must be thoroughly washed • It is essential to bathe on return to the station if contaminated with sewage.

28. Confirmation Assessments will be based on this lesson and the corresponding study note Learning Outcomes • Understand the practical implications of access to sewers through manholes, shafts and chambers • Be aware of ventilation considerations and the danger from sewer gas • Understand the method of effecting rescues from sewers.

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