Initially it posed a problem for developers, but it wasn’t long before the redevelopment of London’s O2 Arena provided a huge hurdle for plumbing engineers to overcome.

It has attracted its fair share of criticism over the past few years, but the Millennium Dome, built originally as a temporary structure for the millennium celebrations in Greenwich, London, UK, has developed into an amazing permanent venue.

The Millennium Dome was intended initially to have a one-year lifespan, but was quickly considered for a long-term purpose and ultimately renamed The O2. Although it sat idle for six and a half years, it was given a multi-million-pounds injection by its new owners and now ranks among the world’s most exciting sports and entertainment precincts.

The O2 has an overall diameter of 365m (400 yards), an internal diameter of 320m (350 yards), a circumference of 1km (.6 mile) and is 50m (54 yards) high at its central point.

Apart from the huge music and sports arena with a seating capacity of 23,000 (which has already hosted some of the biggest rock bands from around the world), The O2 includes a massive 667,000 sq ft of restaurants, bars, retail outlets, night clubs, even a skating rink and exhibition space. There is also an 11-screen cinema complex, an indoor beach, two concert halls and an exhibition space that is currently home to Tutankhamun’s treasures – all housed under the huge tented roof.

When at full capacity, the entire building will be able to hold 60,000 patrons.

The O2’s owners, AEG Europe, claim to have alleviated the ‘50-minute queue for the loo’ by installing 548 toilets; and there lies part of the problem faced by some of the UK’s best plumbing engineers.

For the massive redevelopment, the local Greenwich Council dismissed the use of open stacks within the tented area because of perceived threats of SARS and other airborne viruses.

Enter Studor – a global manufacturer of a range of products which offer solutions for venting buildings’ drainage systems, eliminating the need for roof penetrations.

“Basically, the entire structure underwent a complete rebuild,” says Studor technical manager Steven White, “and this introduced a drainage design problem. Originally it was designed as a temporary structure for the millennium celebrations, having open stacks terminating within the structure.”

With the new design, there weren’t many options left to the developers but to run ventilation to the outside – which happens to be around 180m (196 yards) away – the equivalent in height of a 60-story building. With the Studor System we were able to offer a solution which avoided the need to penetrate the clean lines of the building’s exterior with vent pipes to the atmosphere, providing the sealed drainage system required.”

Normally, vent stacks stabilize the air pressures within the soil stack to maintain it at near atmospheric pressure and help to reduce the incidence of negative and positive transient pressures which have the potential to cause induced siphonage of trap seals within the system – the only barrier between the drainage system and the living space. In extreme cases positive transient pressures can lead to trap water-seals blowing out of or bubbling within the fixture and leaking sewer gases into the building’s interior.

The solution to this has been to use AAVs (Air Admittance Valves) and P.A.P.A.s (Positive Air Pressure Attenuators). Originally developed for high-rise buildings and comprising a large bladder within a cylinder, the P.A.P.A. unit acts like a shock absorber, attenuating pressure waves and stopping them affecting the plumbing system, hence eliminating the need for vent piping and, in the case of The O2, roof penetrations.

Studor, together with the Drainage Research Group at Heriot-Watt University in Edinburgh, Scotland, led by Prof. John A. Swaffield, worked together to develop a suitable system for The O2 and to prove to building control that the system would work.

It was a difficult project because this was breaking new ground for all parties – this type of project hadn’t been done before so no typical model existed.

A major design concern was the potential sewer gas build-up when the arena area was not in use. White explains how the problem was overcome.

“The university team determined that any gas build-up would follow the water flow. By placing all urinals on a 12-hour flush cycle this greatly alleviates the potential of any gas build-up problem. We (Studor), in conjunction with Heriot-Watt University, proposed the sealed system solution to M&E (consulting engineers for the project).

“Together we worked on this unique design, analyzing system operation and also fault occurrences to ensure a safe drainage system design. Inside The O2 all vent terminals are sealed within the structure. However, outside pump stations are situated in external structural pillars with open vents, spaced 300m (328 yards) apart to dispense any odours and utilized to relieve sewer gases generated within the complex.

“With The O2 being planned as a major world-class music, entertainment and sports venue, no expense was spared to ensure building services were of the highest quality and functionality.”

Playing their part

Prof Swaffield explains the university’s role in the system.

“We have developed a concept of a sealed building drainage and vent system that relies on both active control by AAV and P.A.P.A. as well as allowing diversity of discharge to multiple sewer connections to provide airflow paths to vent the system. These considerations allow roof terminations to be dispensed with. The proposed technique was described in a paper titled: Swaffield J.A. Sealed building drainage and vent systems – an application of active air pressure transient control and suppression.’ Building and Environment, 41 (October 2006) pp1435-1446.”

Prof Swaffield confirms that the project was unique. “We believe this is the first time that open roof terminations have been rejected for a system that incorporates planned active control of air pressure transient propagation in response to appliance discharge within a building and drainage system.”

Proving to building control and the Greenwich Council that the system would work was a considerable challenge in itself.

“We simulated the operation of the network under load conditions. The major challenge was adequately representing the boundary condition to represent the range of sewer connections.”

Active control is a relatively new concept. Prof Swaffield says that while AAVs have been available for around 25 years to deal with negative transients, a whole system had to await the development of the Positive Air Pressure Attenuator – a variable volume containment device that reacts to positive air pressure transients within the system – of the sort propagated following a surcharge either at an offset or at the base of the stack.

The success of the modelling and the entire project is reflected in the way the system currently operates at O2.

“Our development of simulation techniques and a reliable computer model allows us to consider a range of system conditions that would not be assessable otherwise without extensive laboratory test rigs. The availability of these simulations does allow us to look at a range of cases not otherwise possible and we do this at regular intervals for a range of clients. In addition we used our simulations to model the SARS event in Amoy Gardens which demonstrated the applicability of the model to forensic post-event investigations.”

Prof Swaffield is constantly engaged in actively working with industry on other applications.