Safe access to drainage
Michelle Fleming from Wavin Plastics explains how access to inspect and maintain drainage systems can be effective and safe
Well-proven tradition or new technology? Direct or remote access? Is the way we build and maintain drainage systems in line with modern construction methods? Designing and building drainage systems, be it for foul water or surface run-off, is a complex task. The design engineers responsible have to take several factors into consideration, such as location and ground conditions, along with the volume and type of sewage or run-off.
The basic rules are laid down in building regulations but they can, however, leave room for various interpretations. One basic fact is that every drainage system needs to be inspected and maintained. Therefore access has to be an integral part of the design. Going back in time, the simplest form of access for inspection were lamp holes. These were openings, put in at regular intervals throughout the drainage system, which allowed for a lamp to be lowered down. A mirror inserted in the next hole down the drain would reflect the light, thus proving the drain was clear and straight.
Although effective for simple inspection, the small opening would not allow any major maintenance or repair of the drain. Part H (England and Wales) of the building regulations names the following types of access point to drainage systems:
According to the regulations, access points should be positioned near the head of each drain run, at a bend or change of direction, where the pipe diameter in a run changes, at a change in gradient and at a junction (unless each run can be cleaned from an access point). Manholes are traditionally the most widely used means of access to drainage systems because they allow direct access to the drain for maintenance personnel. In recent years, there have been increasing concerns over the health and safety aspects of working in confined spaces. Official figures show that 70 people were killed on construction sites in 2003-2004.
Although most fatal accidents resulted from falls from height, a number of fatalities have been attributed to working in confined spaces. According to the Health & Safety Executive a confined space is “any space of an enclosed nature where there is a risk of death or serious injury from hazardous substances or dangerous conditions”. The dangers of confined spaces include lack of oxygen, poisonous gases, fire, dust and hot conditions. In order to comply with health and safety regulations, employers must carry out a risk assessment to decide what safety measures are necessary or face prosecution. Working methods must avoid entering confined spaces where possible.
This has led to the development of other types of access chambers to replace manholes, which allow inspection and maintenance of sewers and drains remotely from the surface. From April 2002 Part H and part M (Scotland) of the building regulations made provision for a deep inspection chamber as an alternative to a manhole, but with restricted entry to ensure accidents and fatalities cannot occur as a result of people falling into the inspection chamber or working in a confined space.
In terms of construction design and management (CDM) a design engineer has a duty of care to design out potential dangers for the client’s health and safety. Design engineers must therefore consider non-entry inspection chambers wherever possible when planning a drainage system. A deep inspection chamber is defined as an inspection chamber that is deeper than 1.2m.
A key factor for this type of unit is that the access must be restricted to a maximum of 300mm x 300mm or 350mm diameter. In many cases the non-entry inspection chamber is interchangeable with a full-size manhole. The Scottish Association of Building Standards Managers, representing the Local Authority Building Standards in Scotland and Scottish Water, have conducted extensive tests of non-man-entry deep access chambers.
The authority has confirmed “they are acceptable in appropriate circumstances and, in particular, acceptable in principle, for use as disconnecting chambers between the private house drains and public sewers”. Although disconnecting chambers are private and not adopted by the water authority, Scottish Water still needed evidence of compliance before allowing their use.
Restricted access, for example, non-entry inspection chambers, do not present any problem for inspection and maintenance work. Trained operatives with the right equipment are able to inspect the drains and sewers remotely from the surface and remove debris if necessary. Drains can also be rodded from the surface. Any major repairs to a drain run will require a trench whether the access for inspection is via a manhole or from the surface, therefore surface access minimises the need to work in a confined space.
Part H of the building regulations also states “small, lightweight access covers should be secured (for example, with screws) to deter unauthorised access”. This is to prevent accidents involving, for example children, entering the chamber or drains. Combined with the appropriate cover and frame combination, inspection chambers, non-entry or not, can guarantee this. At the moment, building and health and safety regulations leave a lot of room for individual interpretations.
Depending on specific interests, on most projects the case can be made for or against the use of a non-entry system. These interests are, however, based on different motivations and drivers. Developers are usually open to new solutions and products if they have been proven to be “fit-for-purpose”.
Key considerations include cost and compliance with building regulations and standards. Non man-entry inspection chambers have been developed to comply with building regulations and various systems have received official approvals such as Local Authority National Type Approval Confederation (LANTAC) and Scottish Type Approval Scheme (STAS), demonstrating their suitability for use on a private sewer system. Building or groundworks contractors will, in most cases, wish to use a system, which is quick and easy to install.
Non-entry systems are lightweight and require less excavation work when compared to a manhole. This makes installation much quicker, easier and safer. They are also more cost-effective to install than full-size manholes and no more expensive to maintain. Building control officers are concerned with building regulations and safety compliance during construction and post-construction.
As already suggested, non-entry systems fully comply with building regulations and particularly with safety regulations. As a result of this, non-entry systems are being more widely used in England, Wales and Scotland on private sewer systems. In public sewer systems, however, the same cannot be claimed.
The UK water and sewerage companies are starting to consider the merits of non-entry systems, however, to date this relatively new technology has not yet been embraced. Asset management is a priority consideration for the UK water and sewerage companies, therefore time-tested performance is usually necessary for new practices to be adopted.
This perhaps over cautious approach obviously ensures the sewerage company is not investing in a new product or system that proves to be unreliable but does, however, mean cost and usage benefits are not taken advantage of as soon as they are available. In the rapidly changing world of the utility market, most sewerage companies are now adopting a more progressive approach to new practices and are keen to trial new systems, particularly if they offer health and safety benefits.
The first steps have been taken by companies such as Scottish Water to accept non-entry systems as disconnecting chambers from the private sewer systems and many are now considering their use as the demarcation chamber from a private property into the public sewer system. There is still some work to be done, however, in ensuring this safer means of inspecting and maintaining sewer systems is more widely adopted throughout the water and sewerage companies.
There is a clear case for the use of non-entry systems in many, but not all applications, but there remains some inertia to its use. Time will tell if non-entry inspection is to gain its true position in the future of drainage inspection.
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