Rebounding after a bomb

The huge bomb which devastated South Quay in London Docklands was one of the last big bombs to hit the UK. Hopefully there will be no more but we may have to face the unpalatable truth that the age of terrorism has some way to run before UK buildings and people can be free of bomb threats. Abroad, these threats are very much alive. This means that there is a market for British skills in refurbishing bombed-out buildings – particularly with the expertise accumulated in refurbishing services after a blast.

The IRA bomb on 9 February 1996 exploded adjacent to the shopping mall at South Quay¹ causing considerable damage to the surrounding buildings, including the eight year old South Quay Plaza 2.

Laing Management engineering services manager George Willsher was tasked with bringing the building back to life, working in cooperation with services consultant Hulley & Kirkwood, and contractors Sulzer Infra UK (mechanical) and Kvaerner Rashleigh Weatherfoil (electrical).

The bomb had an explosive force equivalent to 800 kg of trinitrotoluene (tnt). It left a crater in the ground 2 m deep and 10 m across and damaged a number of underground services.

The blastwave pressure caused by the explosion has been calculated at 75·5 kN/m² at an average distance of 55 m from the building at the middle of the south elevation.

This pressure shattered the external glazing in the curtain walling system. It then passed through the building and entered the ventilation ductwork system, which caused severe damage to the air handling units located in the roof plantroom.

Building services were crippled, but the engineers thought it would still be possible to revive the system: reusing the hvac equipment to breathe life into the building again.

The police moved in to secure the building straight after the bomb. This first hurdle delayed work by several days and it was not possible to isolate and drain down the services. The sump pumps were no longer working either, which caused water damage to the chiller plantroom in the basement.

Then engineers had a real stroke of luck. It was discovered that the main cold water storage tanks located to the south in the roof plantroom had been stripped down for a major refurbishment. This fluke took them out of the frame and, more importantly, meant that the building was not drowned in water – which would have damaged it even more.

The insurance company's initial inspection of the building determined that all of the services in the south side of the building (excluding the sprinkler pipework) were condemned. However, the vav boxes and ductwork on the north side of the building showed no visible signs of damage and the insurers' verdict was that they could be retained.

It was known from the St Mary's Axe and Bishopsgate explosions that ductwork suffers from huge internal pressures during a blast. It is over-stressed and its integrity must be checked before reuse. Tiny fragments of glass accumulate in vav boxes, which would cause a major health and safety hazard if reused.

The insurance company was advised to test the ductwork and remove the vav units to take out the glass. An autopsy of the sixth floor and riser ductwork found that both had failed. All the ductwork in the building was subsequently condemned and stripped out.

It was demonstrated that removing the vav units, cleaning out the glass shards, retesting and reinstating the units on-site would not be cost-effective. Unlike the existing plant, whose warranty had expired, new units would be fully warrantied.

Inspecting the roof plantroom's ahus found that they could be reinstated in-situ – simply replacing the damaged components. Most other major items of plant could also be retained but would be subject to testing once the ductwork systems had been reinstated.

Sequencing for weather protection

Work on putting the services back together started in May 1997, working to a completion date of July 1998. This ran in parallel to refurbishment of the building fabric. Services engineers worked through the building from the ninth floor down, while Scheldbouw, the contractor, rebuilt curtain walling from the ground floor up.

This sequence left the upper floors open to the elements, which would have made installing the services difficult – not to mention damp. A temporary screen was therefore built 1·5 m from the edge of the building, so the floors could be returned to later for completion of the perimeter services and commissioning.

The ahus and motor control panels located in the roof plantroom were mothballed to prevent further damage from the weather.

In December 1997, services engineers advised the insurance company to flush the sprinkler system. Almost inevitably, sediment would have formed while the system was drained down. The insurers agreed to flush the second floor only to gauge the extent of any problem. It was found that the metal had oxidised, causing considerable flaking. If left, this could have blocked the sprinkler head, so it was agreed to flush the complete sprinkler system.

The roof plantroom had to be scaffolded to repair the steelwork and reinstate the cladding. This delayed tests of the ahu heating and cooling coils. In the end, 13 of the 30 coils were found to have been damaged. It is suspected that this was caused shortly after the bombing by frost – deep into February it was cold enough to freeze the water around the coils.

Replacing the coils brought further problems because there was not enough space to remove them. Ultimately, it was necessary to cut them out and replace them with coils manufactured in two sections. The new coils incorporated extra commissioning stations so the four sections could be balanced.

In some ways, the insurer was actually quite enlightened. Their policy had a clause stating that any upgrades required by new Building Regulations will be reimbursed. This meant that the curtain walling could be improved to match current U-value requirements.

Other upgrades included relocating the fire alarm panel in the building management suite, and linking this to a fire telephone system serving all staircase landings.

The existing humidifiers had to be replaced, but it was not possible to do this on a like for like basis. The new humidifiers had a higher electrical power requirement, making it necessary to replace the supply cabling from the motor control panel.

The ahus turned out to have moved following the bomb blast leaving no choice but to replace the anti-vibration mountings on the supply and extract fans.

The ahus operated without a hitch for some three months after the initial commissioning. But then the framework began to show signs of stress – vertical members in the pentapost structure became distorted. The original damage appeared to be making the units implode.

John Heaphy, of quantity surveyor Silk & Frazier, estimates that refurbishing existing plant instead of throwing it away and replacing it saved the insurance company "around a million pounds".

The hurdles faced in reviving this building's services could equally have been found on another refurbishment project. The experience holds lessons UK plc as a whole can use to sell its skills abroad – including to the unfortunate countries where the risk of bombing has yet to be defused.

George Willsher MCIBSE is an engineering services manager at Laing Management.

The management contractor for this project was Laing Management, working for Baxtergate. QS was by Silk & Frazier, with project management by DTZ Debenham Thorpe. The Equus Partnership worked as Acoustic Consultant. This article was written with assistance from services consultant Hulley & Kirkwood, and the contractors: Sulzer Infra (UK) and Kvaerner Rashleigh Weatherfoil.