In particular, when operatives enter the sewerage system, it is vital to observe very high safety standards.
As in all areas of operations, rules are often ignored and while accidents are relatively rare, carelessness creeps in, leading to a growing number of serious injuries and even death.
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.
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 the German Association for Water, Wastewater and Waste’s (DWA) leaflet M 143-17, and the specifications for the mortars in the German Society for Trenchless Technology’s Information sheet number 18.
The DWA advocates the development of a secure and sustainable water industry and is a politically and economically independent organisation that works in the specialist fields of water management, wastewater, waste and the protection of soil.
A German Institute for Standardisation (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, which is the only German approval body for construction products and types of construction.
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 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 not in a confined space, he wears protective goggles against small flying stones and follows health and safety regulations as prescribed.
When jetting at high pressure, a lance of length 700 mm 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 1 m diameter shaft without using the M-Coating apparatus and its components, says Hermes.
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 health and 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 – together with the site manager and the employer – is running an incalculable risk. The contractor scheduling the work is liable because it is assumed that it is known 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. It is now possible for shaft cleaning to be carried out without operators being sent into the shaft and questions of liability no longer arise for the site manager and the contractor.
Shaft coating with 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 that cannot be recoated. They can be circular or rectangular, with a diameter of 600 mm to 3 m, and of any depth. The deepest shaft treated so far measured 25 m.
The coating can also vary between 5-100 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, which contributes to maintaining employees’ health.
It is nearly always the case that sickness in the workplace is only recognised as an industrial disease after it has around for many years, many employees have fallen ill and the law has become involved.
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 still work accurately after eight hours.
To give a clearer comparison of the various systems, we have set out the safety aspects involved, in Table 1.
Conclusion
The ratings given in Table 1 give a clear indication of the advantages of each technique and enable one to choose the right method for specific applications.
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; the slightly higher outlay compared with conventional methods is justified by the efficiency, quality and high safety standards provided.