WET News

wwtonline.co.uk | DECEMBER 2018 WET NEWS 23 manhole cover and frame. When the manhole is constructed, the number of courses used can affect the actual distance to the first step. To assist safe access into and egress from manholes and other chambers, the use of a handhold is strongly recommended. Handholds are not always included as part of the manhole construction and their omission may place operatives at greater risk. Specifiers are advised to consider handholds as an inte- gral part of the manhole design. Caswick offer handholds in various sizes, fixing methods and materials. The handhold remains fully within the cham- ber when not in use and can be easily raised into position once the access cover has been removed. The handhold is locked into position and used to provide stability to the person as they transition from the surface level onto the steps in the cham- ber. When extended, the hand- hold also creates a visual aid to indicate the location of the man- hole to other people in the area. Once work is complete and the operative is out of the chamber, the handhold is lowered back into the chamber beneath the level of the surface until it is required again. The Caswick handhold connects directly onto Caswick steps and does not require tools to operate it once it has been highways drainage is generally managed autonomously and designed to separate regional highways specifications. Product standards and specifications In the United Kingdom, there are harmonised product stand- ards relating specifically to manhole steps and to fixed lad- ders. There are also standards and industry specifications relating to manhole assemblies and standards relating to com- plete drainage systems where requirements for manhole steps, ladders and associated access systems are included in the specification. For innovative products that fall outside the scope of these standards, inde- pendent assessment and third- party certification is advised. In the UK, Type D plastic encapsulated double steps are generally specified. They pro- vide high visibility and corro- sion protection. In most areas, single steps are not allowed. Single steps are considered less safe and those made from cast iron are prone to corrosion and risk of failure. Steps are usually specified for manholes with a depth up to 3.0m from cover level to the sof- fit of the pipe. Fixed ladders are usually specified for manholes with a depth between 3.0m to 6.0m from cover level to the soffit of the pipe. The requirements in some industry specifications may demand different values for steps and ladders than the mini- mum requirements of the prod- uct standard; these can be more onerous than the product stand- ard or they can be less demand- ing. In these situations, it is advisable to consult the contract documents and confirm with the client which specification should take precedent. Differences in quality and performance The process of designers specifying to a product standard to meet a minimum level of performance and the installer procuring products that conform to those standards is an efficient and established method throughout the construc- tion supply chain. However, designers, developers and asset owners should beware. Manholes are dangerous underground con- fined spaces where only authorised personnel should have access with the knowledge, equipment and the security means to carry out rele- vant inspection and maintenance work. In the vast majority of cases, access is made once or twice a year for routine maintenance. Sometimes chambers are not visited for years, only when an incident occurs. When the man- hole cover is li‹ed, the steps or ladders found were probably installed when the system was built. Each step inside the chamber can be a leap of faith. There may be a spectrum of quality for standard-compliant products; those that only mar- ginally conform to the minimum requirements can result in lower long-term performance over the lifetime of the asset. In the case of steps and ladders, this could compromise safety and result in higher whole life (Totex) costs when compared with products of a superior quality that have the potential to perform better, for longer. It is important that specifiers and users understand what they are getting for their money and how added benefits can be real- ised, even when using stand- ard-compliant products. For example, the steel used for Cas- wick manhole steps is high ten- sile steel for precision applica- tions; lower quality steps are not made from high tensile steel and do not provide the same degree of dimensional stability and robustness. As deteriora- tion is progressive, this risk may not be immediately apparent but only become evident over time. Exceedance of minimum standard requirements can therefore provide future-proof- ing to ensure satisfactory long- term performance. Additionally, the preferred material for manhole steps in accordance with most Water Undertakers' Adoption require- ments to ensure sufficient protec- tion from corrosion is plastic encapsulation. Standard Caswick manhole steps use a special grade PP encapsulation which provides greater protection from impact, mechanical and thermal stress cracking and ageing. The actual thickness of the plastic encapsula- tion for Caswick steps is generally in excess of 4mm compared with a minimum requirement of 2.5mm (BS EN13101). These factors are important – plastic becomes brittle as it ages, and if cracks appear in the encapsulation, this can expose the metal underneath and lead to corrosion and, over time, potential failure of the step. Moving between the chamber and the surface The transition from ground level into the manhole chamber on entry and vice versa on exit is a critical part of safe working in a confined space. Most specifications stipulate that the distance from ground level to the top of the first step should be a maximum of 675mm (BS EN752, Sewers for Adoption 8th Edition pre-implementation version, Highway Construction Details, Welsh standards for new gravity foul sewers and lat- eral drains). Sewers for Scotland 3rd Edition requires the distance to be no less than 500mm and no more than 700mm. Within these documents, there are dif- ferent requirements relating to the minimum number of courses of "adjusting" brickwork between the cover slab and the Product standards: Steps (BS EN13101:2002) for manholes and other underground entry chambers Essential Characteristics Requirement Clauses in BS EN13101 Notes Requirement Width of Tread 4.3.2.2c) Test according to clause 5. Min size in mm (dimension T) at least 20mm Stand-off distance (projection) 4.3.2.2e) Test according to clause 5. Min size in mm (dimension P) at least 120mm Vertical loading 4.3.7 Test according to clause 5. Vertical loading in kN with corresponding values of initial and permanent deflections in mm See Table 2 Pull-out/anchorage 4.3.9 Test according to clause 5. Pull-out loading in kN at least 5kN Proof load (grey cast iron) 4.3.8 Test according to clause 5. No visible crack 12kN Impact (where applicable) 4.3.10 Test according to clause 5. Impact resistance demonstrated by step withstanding a mass (kg) dropped from a height (m) 20kg dropped from a height of 1m Twist 4.3.6 Test according to clause 5. Twist demonstrated by variability of front edge of tread from flat surface. Single step: less than 3mm. Double step: at least 5mm Durability 4.1 and 4.3.5 and 4.3.2.2b) where applicable Test according to clause 5 for the relevant requirement 4.3.2.2b) at least 2.5mm for plastic encapsulation Product standards: Ladders (BS EN14396:2004) fixed for manholes and other underground entry chambers Essential Characteristics Requirement clauses in standards Notes Value Design Requirements (width of tread, stand off distance, etc) 4.3 Width of tread at least 300mm. Stand off at least 150mm. 250-300mm between rungs. At least 20mm tread width Load bearing capacity 4.4 Ladders meeting the requirements of 4.4.2 are considered to have satisfactory impact resistance 2.6kN with permanent deflection. At most 0.3% tread and no damage Durability 4.2 Suitable materials specified. Ladders shall be resistant to corrosion. Materials and corroson protection systems selected appropriate to mechanical and chemical loading and thermal stresses according to operating conditions installed. The handhold remains fully within the chamber. Caswick is continuously developing improvements to existing products and develop- ing new solutions to make man- hole access as safe as possible. Examples of recent innovations (with patents applied for) include the Caswick Riser Frame and the Caswick Safety Grate. Manhole safety – a duty of care Making the workplace and the infrastructure around us as safe as possible should be the first priority. All activities from new construction, operation, inspection and maintenance through to decommissioning at the end of asset life should be considered in the original manhole design and its serviceability evaluated continually throughout the operating life. The designer, asset owner, installer and maintenance oper- ator have a duty of care to their employees and to the public to ensure that every activity, authorised or unauthorised, is managed to eliminate risk or to reduce the risk of harm to a min- imum. It is their responsibility to be aware of the best solutions avail- able and to take reasonable meas- ures to assess risk and deploy appropriate techniques to manage safety throughout the asset life.

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