Recent revisions to Building Codes and Regulations contain little to affect the designer's input regarding plumbing and drainage systems.
Instead, the drivers for change have been requirements that have no relationship to hydraulic principles, but are just as important.
Two main issues regard sustainability, writes David George. One is the need to protect the environment by reducing carbon emissions without sacrificing quality of life. The other is about the sustainability of life itself: of those involved in the construction and maintenance of buildings. Both are becoming paramount in the way designers approach their work.
Fortunately, CDM regulations create a refreshing thought process that can reduce carbon emissions and prevent injury and loss of life within the construction industry.
The Health and Safety Executive (HSE) states that 2004 had the highest number of fatalities since 1997 in respect of ground works in trenches.
HSE inspectors are trying to ensure proper risk assessments are undertaken and a more holistic approach is integrated into the design phase.
But it is not always obvious to designers how to reduce potential hazards in drainage systems during construction.
Risk assessors say the longer workers are exposed to a hazard, the greater the risk of injury. So reducing construction time can reduce the risk. It may seem obvious, but some designers are not confident breaking with tradition. CDM regulations simply demand that hazards inherent in a building's design have been considered.
The hazard of trenching can be reduced by considering:
PIPES Generally, once a trench exceeds 1.2m in depth, its sides must be supported to reduce the risk of collapse. But this increases costs and lengthens construction time. This leads to supports being discarded in favour of a clearer work space and a speedier installation.
It can prove fatal.
Designers can mitigate this risk by keeping the pipe close to ground surface level (see diagram 1). They should protect the pipes from damage by choosing a robust pipe material or specifying a bed and surround that offers greater protection strength. The benefits include less excavation, safer trenches and faster installation.
DEATH OF THE MANHOLE Installing pipes in shallow ground will allow you to replace manhole chambers with inspection chambers or rodding point systems.
Any CDM assessment will benefit from having more inspection chambers to satisfy the access requirements. These are simple to assemble and, because of the superior flow characteristics of the chamber bases, are less likely to snag material and cause blockages.
The rodding point system (see diagram 2) allows clearing machinery to enter the drainage system through small-diameter access doors - a safer way to clear blockages from ground level.
Branch connections are made with standard pipe fittings and can take a more direct route to the carrier drain.