| Home | Fire
Safety | Skyscrapers Home Emergencies | Glossary |
|
Some of the essential activities taking place within and around a building are liable to encourage the growth of bacteria, insects and vermin, which could cause pollution, disease and foul smells. It’s therefore necessary to control carefully the conditions most favorable to the development of these unwanted infestations: the provisions for drinking-water, food preparation and washing, and the generation of waste products, refuse and dirt. As far as the building designer is concerned, this involves a careful analysis of suitable water supply and storage systems, and the effective methods of waste and refuse removal. Decisions in these areas must be closely related to the selection of materials least subject to contamination, and the provision in design for efficient cleaning and freedom from deterioration. Drinking-water, food preparation and washing In the US and UK, the supply of water to a building is subject to statutory undertakings, mostly controlled by the provisions of the Water Acts, the Water Industry Act, a separate Water Industry Act and the Water Act. These are supplemented by the Water Supply (Water Fittings) Regulations: Specification for design, installation, testing and maintenance of services supplying water for domestic use within buildings and their curtilages: Specifications for installations inside buildings conveying water for human consumption, Design. They seek to empower the water authorities to protect drinking-water supplies, effect more efficient use of water, enforce prevention of waste, undue consumption, and misuse or contamination of water. Clean and potable water is therefore generally in ample supply even during times of drought and, as the same source is used for all purposes in a building, installations are of simple design. The principal mechanical requirements for the system are that all pipework used should be non-corrodible, capable of being tightly jointed, and resistant to deformation and mechanical damage; the layout of pipework should provide the minimum resistance to water flow and should be protected from freezing; and forming, sup porting and connecting techniques to appliances should reduce the possibility of noise generation and transmission. The water supply system or plumbing allows the water not intended for human consumption to be stored in a replenishable cistern, incorporating its own feed system to sanitary appliances such as WCs, bidets, basins and baths; washdown points; and the hot water system supplied via another storage vessel and cylinder. The provision of separate water storage facilities, isolated from the mains, reduces the risk of misuse and contamination of the water within the rising main. Misuse could adversely affect the supply source, as well as the water to be used for direct human consumption (drinking and food preparation) within a building. The storage cistern also ensures a continued supply of water in the event of the mains supply being cut off for a short period due to damage or maintenance work. By installing the storage tank at high level in a building, sufficient supply pressure can be ensured. However, if the pressure of the water in the mains supply is insufficient or likely to fluctuate dramatically owing to demand, the mains water must be pumped to the required level for a building to be adequately serviced. ----1 Typical traditional domestic water supply system (pipe sizes are for outside diameter copper). ----2 Principles of a mains-fed hot-water and heating system. It’s usual to provide a cold water storage cistern as this assists in reducing the size of the pipe used for the mains supply. To avoid the possibility of pollution, there must be a clear gap between the float-valve-controlled water outlet of the supply pipe and the top surface of the stored water; the gap is maintained by siting an overflow pipe at a distance below the supply pipe. Regulation of the flow of water is achieved by a hollow plastic ball attached to the valve mechanism. A similar air gap must be provided between the outlets on taps supplying water to sanitary fitments, e.g. bath, basin, etc., and the spillover level or rim of these fitments. An overflow will normally control overspill, but this is ignored for provision of an air gap, as it could be obstructed. As a result of research based on systems in North America and some European countries, most ---- local authorities now allow taps to sanitary appliances to be fed directly from the mains without involving water storage cisterns. --- indicates such a plumbing system, and pollution is prevented by using an anti-vacuum valve which maintains a positive pressure in the system to prevent any possibility of water backflow (back syphonage). Sealed hot water heating systems are currently used, but the diagram also indicates a sealed system for the hot water supply. The latter is similar to that which is widely employed in other EU countries and has now been introduced. In addition to the mechanical and technical criteria, it’s very important that detailed consideration is given to the appearance of a water supply system within a building. Pipework, ancillary devices and appliances must be carefully integrated as an essential part of the design of a building. No plumbing system should 'occur' in a building as an afterthought; if adequately considered during the early stages of design, the system can enhance the appearance of purely practical areas, or be successfully concealed in other areas by incorporation with other services within structural elements, e.g. wall, floor and roof construction. Waste products, refuse , dirt Depending upon its precise function, a building usually must also provide installations which facilitate the disposal of water-borne organic waste matter, including human excrement (sewage); permit the collection of rainwater otherwise liable to cause some form of deterioration; and allow other organic and non-organic waste (refuse) to be removed. Sanitary fittings (WCs, bidets, urinals, baths, showers, basins and sinks) which receive the sewage are designed on the basis of specific anthropometric data for efficient function; they also flush away bacteria, and prevent foul smells. They are manufactured from non-porous, smooth, durable and easily cleaned materials, and they incorporate a water-filled trap to prevent gases escaping into the building from the pipework beyond. Further precautions against smells and other forms of pollution are provided by building designs which promote good ventilation in rooms used for bathrooms, laboratories, operating theatres, abattoirs, etc., where sanitary appliances are situated; by ensuring adequate space around a building; and by its correct location within a particular environment. ---- Plastic cesspool and septic tank set below ground in concreted surround. ----Typical centralized single stack sanitary installation and drainage for small building. Drainage systems The sanitary fittings discharge sewage along a network of gas- and watertight pipes which together form the drainage system of a building. This system conveys both solids and liquids to a treatment plant in the local authority sewage works or, if this plant is not available, to a cesspool or septic tank and filter bed in close proximity. Pipes which convey liquids only are generally called waste pipes, and those which convey solid matter and liquids are called soil pipes. Efficient and economic design considerations usually mean that the waste and soil pipe system in a building takes one of two forms. The simplest occurs when sanitary appliances can be fairly closely grouped around vertical discharge stacks (soil and waste pipes) which then convey sewage by the most direct route to underground drains. Such installations are found in many types of buildings, including blocks of flats, where the activities to be accommodated allow vertically repetitive planning arrangements. It’s now usual to combine the soil and the waste pipe into a centralized single discharge stack sys tem; the overall dimensions of this pipe are dictated by the amount and frequency of solid material it must transfer to the drains. Great care must be taken when designing the system to ensure that the water seals or traps in the sanitary fittings are not prevented from reforming after use. Seals may not reform because of induced syphonage, which occurs when the seal is sucked away by the force of water discharging from branch pipes on other floors as it passes down the vertical discharge stack. The rush of water down the stack absorbs air from the branch pipe of the fittings below and this causes the external air pressure on the seal to force the water out of the trap. This syphonic action can be prevented by ventilation pipes (antisyphon pipes) on the drain side of the sanitary fitting to equalize air pressure within the main stack. Alternatively, special antisyphon resealing traps can be used, which let air into the system without complete loss of trap seal. Nowadays it’s more usual to design the whole drainage system with careful regard to sizes, lengths, slopes and positioning of pipework. Design rules are based upon empirical and scientific analysis of water flow and air pressure characteristics. A variation suitable for repetitive domestic installations uses an air admittance valve at the top of the discharge stack. It does not allow foul air to escape and therefore can be located within the roof space to reduce installation and roofing costs. It also eliminates the unsightly stack projecting through the roof slope. However, every fifth dwelling must have a conventional stack to ventilate the sewer. When the activities within a building are complex and it’s not possible to group sanitary fittings around a centralized stack -- as in hospitals, schools and certain office layouts -- a satisfactory drainage system can be accomplished by grouping fittings in 'islands', and by providing extensive horizontal pipework connection to strategically located vertical soil and/or waste stacks. This system is expensive and more complicated than the centralized system because the necessary proliferation of horizontal pipes not only makes concealment by 'false' ceilings necessary, but also means that further syphonage problems must be overcome. Overlong horizontal lengths of pipework are liable to cause the discharged water from a sanitary fitting to remove the trap seal by self-syphonage. This occurs when a horizontal pipe flows full and prevents a build-up of positive pressure on the drain side of the trap until the last of the water has been drawn away. Fortunately, baths and large flat-bottomed sinks rarely suffer self-syphonage; this is because the last of the discharging water moves very slowly, allowing the seal to resettle, and the waste pipe of a WC is too large to flow at full bore. For other sanitary fittings with extensive horizontal lengths of pipework, larger sizes of pipe and greater depth of seal must be incorporated, and also probably an elaborate ventilating system. Rainwater collection A drainage system for the removal of waste should be planned in conjunction with the drainage system required for the collection of rainwater. This involves collection of rainwater falling on a building and perhaps around a building. The collected rainwater must then be conveyed in a similar manner as waste water to a local authority surface water drain. If this drain is not available, rainwater can be taken to a purpose-built soakaway situated away from areas likely to be detrimentally affected by excessive amounts of water, or to a conveniently located water course or a storage vessel for subsequent use as a water supply. Water falling on a building at roof level is collected and discharged into a rainwater pipe system by means of strategically located rainwater outlets. If a building is lower than about 5 storeys, easier means of access and maintenance generally make a system of collection involving guttering more acceptable. The water is conveyed to the vertical rainwater pipes, which discharge either directly into the drain below ground or over trap-seal gulleys at ground level. Pipe sizes for the design of rainwater drainage systems depend upon the expected risk involved: 50 mm/h of rainfall for flat roofs and other open paved areas; 75 mm/h for sloping roofs; or 150 mm/h when very occasional overflowing of rainwater outlets or gutters cannot be tolerated. (This amount is likely to fall only during short periods of heavy storms.) When considered together, there are three basic drainage systems approved by local authorities for the disposal of soil, waste and rainwater. Combined system: Both drains discharge into a common sewer. This is a simple and economic system because it involves less pipework and is easy to maintain. However, it has the disadvantage that vast amounts of liquids must pass through the sewage treatment works, particularly after heavy rainfall. Separate system: Two drains are provided. One of them receives the collected rainwater (or surface water) and conveys it directly to a suitable outfall without treatment, e.g. nearby water course or river. The second drain takes the soil and waste discharge and conveys it to the sewage treatment installation. This obviously involves more drainage pipes, but avoids the risk of overcharging the sewage treatment plant during periods following heavy rainfall. Partially separate system: A combined drain is used for soil, waste and rainfall. However, a second drain is also available to regulate the amount of rain or surface water discharging into the combined drain, according to the capacity of the sewage treatment installation. This may be by connecting some of the rainwater pipes and drains to the foul water drain. ---- Rainwater collection and methods of disposal. ---- Domestic drainage system: (a) combined drainage system; (b) separate drainage system; (c) partially separate drainage system. IC = inspection chamber, RWP = rainwater pipe. Table of Maximum spacing (m) of access facilities in drains up to 300 mm in diameter: Small access fitting | Large access fitting | Junction | IC | Manhole Drain Access Access to drains is necessary for inspection, testing and maintenance. The following means are acceptable:
Rodding eyes may be used at the head of a drain. They are in effect an extension of the drain up to surface level, terminated with an adaptor to a screw-sealed surface access plate. Access fittings are produced in plastic or clayware to suit the drainage system material. They too are limited to rodding, but in both directions. Fittings may be cut or adapted for depths up to 600 mm to invert (invert represents the lowest level that water will flow in a drainage channel). Inspection chambers are produced from a range of materials including brickwork, preformed plastic units and precast concrete sections. Each provides the option of a few branch channels in addition to through-flow. Limited bodily access is possible in depths of up to 1 m to invert. Manholes are sufficiently spacious at drain level for a person to work in. In depths over 1 m they require step irons or an attached ladder to aid accessibility. They are generally built of concrete (in situ or precast) or dense masonry to provide adequate strengths at depths of several meters. Note that small surface access plates are secured by screws to prevent unwarranted access, e.g. by children. Siting of access points should occur:
Systems Integration Whatever internal drainage arrangements are to be incorporated within a building, it’s always important to consider carefully their implication on the precise system to be adopted. Not only can considerable economy be achieved by adopting simple systems, but also the visual impact on a building can be quite considerable; pipework can be exposed, or concealed in service walls, floors or ducts, and false ceilings, etc. When requirements for buildings were much simpler, drainage specialists could arrive on site and, after initial competition for space with other trades, install their services. The new approach to the design of installation leading from a more sophisticated knowledge, together with the standardization of components for greater economy, now requires designers to give much greater thought to the incorporation of even simple drainage systems in a building. Indeed, the integration and coordination of services in relation to structures as a whole now becomes a paramount design criterion for such buildings as blocks of flats, offices, hospitals and schools, where all the engineering services (heating, lighting, plumbing, drainage, etc.) could account for 25-50 % of the overall capital costs. Problems relating to the installation of gas, electricity and telecommunications services are discussed here. Refuse collection / disposal It’s usually necessary for a building to incorporate adequate arrangements in its design for the collection and subsequent disposal of refuse. Methods which can be adopted for this will only operate efficiently if the precise type, form and amount of waste produce has been successfully identified(or anticipated) during the early stages of design investigation. Consideration may then be accurately given to efficient movement patterns of refuse about a proposed building and their influence on required standards of hygiene and safety. Generally, storage for more than a few hours within a building is undesirable, and the small receptacles in which refuse can conveniently be placed temporarily need frequent emptying. Unobstructed and direct circulation routes to facilitate refuse collection from a building should also be thoroughly planned, thereby furthering the desire for protection from the pollution caused by unpleasant smells, visual horrors and noise. Refuse which is not destroyed at source is taken to local sites where crude selection may take place to permit incineration, consolidation and/or transportation to centralized tips. Some non-toxic refuse may be used to backfill areas subsequently needed for building sites, or used for other forms of land reclamation. The design criteria for a building will vary when considering refuse collection and disposal methods applicable to medical, commercial, industrial or domestic activities, For example. A building designed to accommodate complex or multi-purpose activities (hospitals and certain factories) can generate many forms of waste, sometimes toxic, sometimes individually bulky, or sometimes accumulating in vast quantities over relatively short periods. Then different disposal systems, some incorporating incinerators, may have to be adopted within a building, requiring great skill from the designer to ensure maximum operational efficiency. But when convenient to the size and form of refuse, disposal can be satisfactorily accomplished by an independent water-borne pipe system installed within a building. This is very similar to the soil and waste drainage system already described, except that the refuse is conveyed to an external pit, from which it’s collected by specialists at convenient time intervals. Less costly methods are available, one of which involves the use of a dry chute, suitable for medium-rise multi-storey flats or maisonettes. The method consists of a vertical arrangement of jointed impervious pipes to provide a tube into which refuse is placed via a chute. The outlet of the tube deposits the refuse into bins conveniently located to facilitate mechanical emptying by the vehicles of the local authority cleansing department. ---- Refuse chute. Small amounts of refuse, such as are generated in houses, can be conveniently stored in dustbins or plastic bags for eventual collection by the local authority. Some domestic refuse--generally waste matter that putrefies - can be forced through a grinding unit below a sink unit, which then allows it to pass through a normal waste pipe and into the drainage system beyond. Previous: Lighting and ventilation |