Accessing the pillars of one of Britain’s busiest road bridges is no easy task, especially when they loom hundreds of feet above the River Thames. It was a challenge not lost on aircraft warning lighting installation specialists, the Delta Group, whose subsidiary company Delta International Steeplejacks (DSJ) recently replaced the aircraft warning system on the Queen Elizabeth II road bridge across the Thames in Dartford.
At 137m high, the bridge is Britain’s second highest cable-stayed road bridge (behind the Severn Crossing), but due to its role linking northern and southern sections of the M25 it is easily Britain’s busiest, with 180,000 cars passing over it daily. When renovation, cleaning or maintenance work is required, careful consideration needs to be taken to ensure access is quick, effective and, most importantly, safe.
Its location under the flight path of nearby London City Airport means its visibility to descending pilots is of utmost importance, particularly at night. Since 1991, its pillars have been illuminated by an arrangement of white xenon flashers, but recent changes to civil aviation legislation have banned their use prompting the need for a full system overhaul.
That task was put out to tender by the bridge’s controlling authority in August 2008 and the contract was subsequently awarded to DSJ’s sister company Delta Obstruction Lighting (DOL), who specialise in designing and manufacturing Aircraft Warning lighting systems. DOL managing director, Tariq Mukhtar said: “We were delighted to be awarded the QEII job because it was a mark of how far we’ve come and of what we are capable of.”
DOL’s brief was to design, manufacture and install a lighting system that was compatible with the bridge’s remote-controlled supervisory control and data acquisition (SCADA) framework, with six lights at each fixing point lasting at least 100,000 hours. It subsequently commissioned DSJ for the installation phase.
DOL’s innovative approach was illustrated perfectly on the pre-installation scouting mission, when the design team’s proposal to incorporate both duty and standby at each fixing point was eagerly accepted by the bridge’s contractors.
After pursuing a number of ways of doing this, including fitting duty, standby side by side and one on top of the other, DOL developed the Dual WL2500 (duty and standby) medium-intensity aviation obstruction light, which incorporates both duty and standby LEDs within one casing – an industry first.
With six of the WL2500s ready to go, a four strong team of highly skilled DSJ operatives headed to London in late January to carry out first fix installation. Their task over five days was to fit a single light at mid level – 50m above deck – on each of the bridge’s four pillars and a further light on the upper levels of the southwest and northeast pillars – 100m above deck level.
Tariq’s brother, DOL operations manager, Asif Mukhtar led the DSJ team. He said: “Access to the bridge was particularly tricky. A service lift inside each tower and a hand-railed platform at each level made work up the tower relatively safe, but the only way to get to the pillars was from the A282’s inside lanes and, with such incredible volumes of traffic crossing the bridge daily, that was no easy task.”
The tough decision was made to close one lane of the four-lane carriageway for 10min each morning and again when the team needed to disembark each evening. Each time, temporary speed limits were introduced and a roadblock of six highway trucks ushered vehicles into the central lanes to protect Delta’s team.
Beginning on the southeast tower, the four men used ropes and harnesses to access parts of the tower unreachable from the platform. They worked their way northwards, using the already laid cable from the previous system as a feed for the WL2500s. Despite bitterly cold and windy conditions, the job flowed without snag as the lights were attached to the bridge with a bracket and pole.
Asif said: “Our lads have installed systems on BT towers in the Outer Hebrides so they are well used to unfavourable conditions. In January, the main issue was time. We aimed to be off the bridge before nightfall each day, but the short days put extra pressure on us,” added Asif.
DSJ’s first fix was finished within the five days allocated and a test was carried out in accordance with the Institute of Engineering and Technology (IET) BS 7671 17th edition – a British standard. The team then returned to Oldham to await further instruction from the bridge’s chief contractors. They have since been called back twice to overcome snags relating to interfacing with the previous system. The system has now passed a function test and testing to ensure that it has fully interfaced with the bridge’s control tower. It has now been signed off by the client.
Tariq said: “It’s very important we take on huge structures like the QE2 Bridge and do a first class job. It is the ultimate shop window for us as it demonstrates to thousands that our products are of excellent build quality and our workforce is highly skilled at fitting them.”