Book - School of Science and Technology

External distribution systems 173PedestrianareasLink bridgeAccess coverVandal-proofenclosureGarageFigure 6.22 External pipework protected by overhead walkwaysoffer the prospect of other routes for external piping, as shown in Figure 6.22, whereprotection to insulation by way of cladding may not be required.Basements and subwaysIn an era when the availability of skilled plant operators is limited, it is more than everdesirable that full consideration should be given to facilities for the day-to-day routine ofpreventative maintenance. The existence of a basement corridor through which pipeworkmay be routed is a bonus in this respect, in particular where no suspended ceiling is fittedbelow the service route. Between buildings, a tunnel or subway of sensible size is needed:by the time that an excavation has been made and a waterproof construction formed, it isbarely relevant in terms of real cost whether the cross-section is 1.5 m by 1.5 m or a metrebigger either way.In terms of pipework installation, what little saving might have been made in constructingthe small tunnel, rather than the larger subway, will have been swallowed up as aresult of the sheer difficulty of working on hands and knees. As to subsequent maintenance,leaking valve glands, dripping joints, distorted flanges, corroded supports anddamaged insulation would all go unnoticed were they to occur in the small tunnel.Underground ducts, etc.Traditional methods of pipe enclosure underground have of recent years come underscrutiny, particularly since practice in the USA and in Europe was known to be atvariance with that in the British Isles. Following an expected pattern, developments inNorth America have been towards the production of relatively complex factory builtunits, with intent to reduce site works to a minimum. In contrast, European tendencieshave been either towards simplification in choice of materials or to adapt and refinetransatlantic usage.The principal hazard to which underground enclosures are exposed is ground watersince, when an excavation is made preparatory to the construction work proper, the