No place for tunnel vision
At the time, the experts reckoned the 600-metre long Jack Lynch Tunnel, which runs under the river Lee from Mahon to Dunkettle, would take up to 18,000 vehicles a day out of Cork city.
But over the last decade, the double-bore four-lane tunnel on the N25, administered by the National Roads Authority (NRA) and managed by Cork City Council, has become one of the state’s busiest road arteries — handling up to 50,000 vehicles per day at weekends, rising to an incredible 68,000 vehicles every weekday.
Now, it’s poised to close for six nights a week from early next year for its biggest safety upgrade — a massive retrofitting of fire retardant slabs to the tunnel walls to bring it into line with new EU standards.
Contractors will bolt high-quality calcium silicate cement boards to the walls and ceiling of the tunnel structure.
It is the first project of its kind in Ireland.
The design and build contract, estimated to be worth up to €7 million, is being funded by the NRA.
The initial proposal to carry out the work seven nights a week over six months, running right through the Christmas period, sparked outrage amongst the city’s business leaders. But following lengthy talks a compromise has been agreed.
The works are now set to begin in the second week of January. The timings of the closures have also been scaled back, to facilitate businesses.
Both tunnel bores will close to traffic six nights a week, from 9.30pm to 6.30am, for six months, The tunnel will remain open every Friday night.
City officials hope the compromise will ensure the works can be done as efficiently, quickly and safely as possible, while minimising disruption to both motorists and businesses.
Engineers, conscious of the impact the closure will have on motorists and businesses, stress they have no choice but to carry out the upgrade.
It is based on recommendations arising from EU regulations following the 1999 Mont Blanc Tunnel disaster.
A total of 39 people died when a Belgian transport truck carrying flour and margarine caught fire in the 11.5km tunnel which runs under Mont Blanc mountain, linking Chamonix in France to Courmayeur in Italy.
Most drivers who were caught in the inferno rolled up their windows and waited for rescue. But the tunnel’s ventilation system drove toxic smoke back down the tunnel faster than anyone could run to safety.
The fumes quickly filled the tunnel and stalled vehicle engines which needed oxygen to run.
Many drivers near the blaze who attempted to leave their cars and seek refuge points were quickly overcome.
Some victims escaped to the tunnel’s fire cubicles — fire-door sealed small rooms set into the tunnel walls every 600 metres.
The fire doors were rated to survive for two hours but the tunnel fire burned for 56 hours and reached temperatures of 1,000 degrees Celsius.
A total of 27 people died in their vehicles. Ten died trying to escape on foot. Of the initial 50 people trapped by the fire, 12 survived.
It took five days for the tunnel to cool sufficiently for anyone to go back in to start repairs.
The tunnel remained closed for three years for renovations and a massive overhaul of fire detection and safety systems.
Cork City Council engineers say their decision to close both bores of the Jack Lynch tunnel for the duration of the works, instead of introducing a contra-flow operation in one bore, is based on a detailed risk assessment and international best practice.
To outline the complexities and risks involved in closing one of the state’s busiest roads, I was invited to watch tunnel manager, Dan O’Neill, coordinate his, and the tunnel’s, 49th maintenance closure last Tuesday.
The work — carried out every three months — makes up part of the tunnel’s annual €2m maintenance bill.
A fleet of maintenance vehicles began gathering around the tunnel maintenance building, located on the Dunkettle side of the tunnel, from early on Tuesday evening ahead of the scheduled 8pm closure.
Up to 70 men in hi-vis jackets waited for the go-ahead from Mr O’Neill.
I thought it would be a simple process — throw a few traffic cones onto the road and switch on the ‘tunnel closed signs’.
But when a hush fell in Mr O’Neill’s control room just before 8pm, and I saw the CCTV screens showing hundreds of cars and trucks whizzing through the tunnel, I realised just how difficult it was going to be.
Traffic management experts, Fitzpatrick’s, were first to roll, beginning a carefully choreographed sequence of lane closures.
One of their large trucks, with a massive “stay left” flashing arrow facing oncoming traffic and a special air cushion at the rear to protect against collisions, drove along the N25’s northbound lane, about a mile from the tunnel leading to Mahon Point shopping centre, and dropped traffic cones to gradually close this lane.
Mr O’Neill used a joystick in his control room to swivel CCTV cameras and monitor the operation — in constant contact by walkie talkie with crews on the ground.
He also used a special computer programme, called SCADA, to automatically switch road signs up to 8km away warning motorists of the impending closure.
Fitzpatrick’s closed the northbound slow lane next, and diverted traffic up onto the ramp to Mahon Point.
Then they closed the off-ramp leading from Mahon Point to the tunnel, effectively closing the tunnel’s northbound bore to traffic.
The final step was to shut off access from the Dunkettle roundabout to the southbound bores. The entire operation was completed by 8.50pm.
Mr O’Neill then gave the signal for the maintenance crews at the management building to roll out.
Cars, jeeps, specialist washing trucks from Britain, and elevator platforms were driven the wrong way down the tunnel maintenance ramp, towards the Dunkettle roundabout, before swinging left into the southbound bore.
This is one of the key reasons why a contra-flow operation during the safety works wouldn’t work, city council senior engineer, Tony O’Sullivan said.
“If a contra-flow was in operation in the southbound bore, contractors trying to get access to the northbound bore would have to cross two lanes of traffic,” he said.
“Strict health and safety rules, and a risk-management assessment have deemed a contra-flow system simply too dangerous to implement.”
Mr O’Neill then played a 2005 CCTV clip taken from inside the tunnel showing a car ablaze.
The fire began slowly near the car’s front right wheel as it drove in the slow-lane of the southbound bore, before its occupants abandoned it.
Within minutes, the flames had taken hold of the front of the car and were shooting up to four metres towards the tunnel roof, filling the bore with thick black smoke.
Mr O’Neill points out a phenomenon called “back-layering”.
Air, which flows through the tunnel at an average speed of three metres per second, can cause smoke to arch, and blow back on itself.
If a contra-flow system was in operation during a fire like this, tunnel managers would have to make an impossible decision — to turn on the tunnel’s extractors fans and decide against which lane of traffic to blow the smoke.
In the case of the 2005 incident, fire fighters were on the scene within minutes and no-one was injured.
But Mr O’Sullivan said the incident highlights the risk of contra-flow.
Engineers who oversaw similar fire safety upgrades on the Dartford Tunnel in London, and who are overseeing the work on the Tyne Tunnel in Newcastle, also opted for complete closure, rather than contra-flow.
Maintenance crew worked through the night, before the tunnel was reopened just after 6am for morning rush-hour. The same operation took place on Wednesday night.
As Tuesday’s maintenance continued, Mr O’Neill led a group of contractors hoping to bid for the fire safety upgrade, on a walk-through tour of the tunnel. A Texan company is among those interested in bidding.
The contract will be awarded before Christmas, with works due to get under way by January 9.
