Working in Manhole Shafts & in Sewers Demands Extra Care with Safety Issues

Working in shafts and sewers has always been dangerous, since they are affected by dirt, noise, humidity and in some cases sewer gases.

In particular, when operatives enter the sewerage system, it is vital to observe very high safety standards. Unfortunately, as in all areas of operations, here too the rules are often ignored. Where accidents are relatively rare, carelessness creeps in, leading to a growing number of serious injuries and even deaths.
Wherever working inside the shaft or sewer can be limited as far as possible, or even avoided altogether, while maintaining high safety standards, then risk to the workforce is kept to a minimum.

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There are many methods currently available for rehabilitating sewer shafts. The principal method is to coat the shaft with cement-based mortar. The techniques are described in DWA’s leaflet M 143-17, and the specifications for the mortars in GSTT’s Information sheet nº 18. A DIN standard is in preparation, to be called DIN 19573. It will be based on EN 1504.  DWA M 143-17 covers coating by hand, the wet spray technique and the centrifugal spray procedure. The M-COATING centrifugal spray process developed by Hermes Technologie of Schwerte is the only such process to have achieved DiBt approval. This process, which is also approved for use in drinking water protection zone, comprises cleaning, sealing off leaks, injection even in the worst cases of erosion or groundwater infiltration, and coating.

M-COATING: Cleaning with the Highest Safety Standards

In the M-Coating procedure, Hermes Technologie offers fully automated shaft cleaning using high pressure water jets and, in the latest version, fully automated sand-and-water blasting. This technique removes the need to go into the shaft in order to perform the blast-cleaning procedure. The whole operation is set up and observed from above, outside the shaft. Although the operator is not in close proximity to the jet nozzles and hence not in a confined space, nevertheless he wears protective goggles against small flying stones and follows the UV regulations as prescribed. When jetting at high pressure, a lance of length 70 cm is stipulated. It is also true that blast-cleaning is best when the jet strikes at right angles. It is questionable whether this is feasible in a 100 cm diameter shaft without using the M-Coating apparatus and its components.

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In practice, operators decide on what they suppose is a good position to work from, shorten the lance, work inside the shaft and so constantly break the UV safety rules. Moreover, jet-blasting inside the shaft means that it is not possible to take measurements of gas levels: there is no equipment that can continue to function in the presence of such large amounts of water. By taking this approach, the operator – and with him, his site manager and his employer – is running an incalculable risk. The contractor scheduling the work is liable because it is assumed that he knows that the work is not being carried out in compliance with the rules.

Where the M-Coating system with the TSSR or the HDS jet is used, the picture is completely different. Cleaning is automated and is directed from above, outside the shaft. Thus it is possible nowadays for shaft-cleaning to be carried out without operators being sent into the shaft. Questions of liability no longer arise for the site manager and the contractor.

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Shaft Coating with the Same High Safety Standards   

Even when coating shafts, it is no longer necessary for operators to stand inside the shaft, thus avoiding the immediate dangers  presented by wet spray coating or coating by hand in confined spaces. Young operators in particular often underestimate the health risk posed by working day after day in wet shafts.  In the past this was unavoidable, but today the M-Coating system has been developed with particular regard to the health of the operator. There are hardly any shafts which cannot be recoated. They can be circular or rectangular, with a diameter of from 60cm to 300cm, and of any depth. The deepest shaft treated so far measured 25 m.  The coating, too, can vary as required between 5 mm and 100 mm. The cement-based ERGELIT mortars used have very positive ratings both from an environmental point of view and with regard to their impact on health. The dry mortar is mixed with drinking-quality water, and the cleaning is carried out using drinking-quality water, so that using ERGELIT dry mortars is a real contribution to maintaining employees’ health.

It is nearly always the case that sickness in the workplace is only recognized as an industrial disease after it has around for many years, many employees have fallen ill  and the law has become involved. Prudent employers must take this into account and from the outset plan techniques and materials that are not a cause for concern because employees are never exposed to immediate danger. If user-friendly equipment like the M-Coating system is adopted, there is an immediate benefit in terms of the employees’ working conditions, which is the first step towards excellent quality assurance! When working conditions reflect high technical standards, workers make fewer mistakes. They do not tire so quickly and are still working accurately after 8 hours. Even older workers can perform skilled tasks in difficult situations such as manhole shafts. It is difficult to send a 62-year-old employee into a shaft to coat it, but he can easily supervise operations from the top, since everything is automated. The M-Coating system means that this employee can continue to work up to 67.

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To give a clearer comparison of the various systems, we have set out the safety aspects involved, in Table 1.

A comparative rating of shaft renovation systems: the techniques contrasted.

Ratings:
– – = poor
+ = good
– = suitable to only a limited extent
+ + = very good
N = satisfactory
Criteria
Manual Method
Spray coating (Dense flow)
>M-Coating System
RequirementsElectricity – water
High pressure cleaner
Electricity – water
High pressure cleaner
Water
Rating
N
N
++
Effort involved in cleaning structureHigh, labour intensive and high riskHigh, labour intensive and high riskVery low,automated and safe
Rating
++
Operational Safety RatingCritical, long time spent in shaftCritical, long time spent in shaftHigh level of safety, short time spent in shaft
Rating
++
Complexity of OperationSimple, but time-consuming and requires experienceJetting certificate and experience requiredSimple, since automated
Rating
+
N
++
 Bonding coatEssentialNot required – occurs as part of processNot required -occurs as part of process>
Rating
++
++
Application of materialWet-on-wet on bonding coat, so stress factorSteady application requires experienced operatorsAutomated control, therefore simple
Rating
+
++
Evenness of coatingRequires experienced operatorsNo problem for experienced jet- operatorsAutomated control
Rating
N
+
++
Surface finishSmooth, looks attractiveRough  sprayed finish, looks satisfactoryOrange-peel, looks good
Rating
++
N
_
Material consumed Optimal where staff are experiencedAlmost optimal given low rebound (approx >5%)Close to optimal, rebound limited by system to approx 2 %
Rating
++
+
+
Choice of materialWide choice, many manufacturersWide choice, many manufacturersOnly using thewide range of ERGELITmaterials
Rating
++
++
+
Follow-up treatmentMin. 3 days, better 7 daysMin. 3 days, better 7 daysMin. 3 days, better 7 days
Rating
N
N
N
Areas of applicationAll types of structure, smaller surface areasAll types of structureCircular structures,and rectangular upto a L:B ratio of 1:1.5
Rating
+
++
+
Shaft diameter> 0.8 m> 1.00 m> 0.5m  to < 3.00m
Rating
+
++
+
Possible profilesAny possibleAny possibleAny possible, but manual finishing may be required in some cases
Rating
++
++
+
Depth of structure Any possible, with scaffolding, safety measures and ventilationAny possible, with scaffolding, safety measures and ventilationFrom 0-30 m withoutany additional facilities
Rating
N
N
+
Staffing requiredMin 2-3 operatorsMin 2-32
Rating
N
N
+
Need to clean up tools & equipmentLowHighHigh
Rating
+
Cost of purchasing tools and equipmentLowHighHigh
Rating
+
Quality of executionDepends on staff, can varyDepends on staff, can varyQuality constantsince processautomated
Rating
++
Analysis of over-all ratingsManual Method
+  = 16
N = 5
– =  7
Spray coating (Dense flow)
+ = 13
N = 6
–  = 6
M-Coating System
+ = 24
N = 1
– = 2

Conclusion

The ratings given above give a clear indication of the advantages of each technique and enable one to choose the right method for specific applications.

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The observations contained in the text and ratings table above highlight safety aspects. Safety in the workplace is a matter of economics. Industrial accidents create unforeseen and incalculable costs in terms of sick days, delays and missed deadlines. When choosing an operating method, the possibly higher outlay should not deter one from opting for modern, machine-aided techniques. Shaft rehabilitation is the M-Coating system’s speciality, no other technique offers so many advantages when it comes to rehabilitating and recoating shafts. The slightly higher outlay compared with conventional methods is justified by the efficiency, quality and high safety standards provided.

In addition, it must be borne in mind nowadays that employees in the workplace are getting older. Automation is the key to maintaining their operational efficiency.  

This article was submitted by Hermes Technologie Ltd., which is headquartered in East Sussex, United Kingdom.

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