The role of national codes in drainage and vent system design
The complex nature of the unsteady water and entrained airflow conditions within building drainage networks have been discussed in this book. It is important to understand that during the early stages of drainage and vent system development, in the late 1800s, the necessary analytical and experimental monitoring techniques and equipment were not available to assist in the design of safe sanitation systems that would meet the requirement that both odour ingress and cross-contamination were avoided by retention of appliance trap seals. National codes were developed based primarily on ‘what was known to work’ at the time. While early enlightened researchers such as Putnam (1911) recognised the fluid mechanics principles underlying system operation, in general this insight was not available. Thus, in a Darwinian sense, each ‘legislative’ zone developed in isolation, with design advances sometimes, but not always, making the transition between zones, for example the US experience of internal systems in the 1920-30 period led to the ‘one-pipe system’ being adopted in Europe. However the principles of the UK single stack system, introduced in the 1960s and currently also acceptable in Australia, were not recognised in the USA until the ‘invention’ of the Philadelphia system in the 1990s.