When the tunnellers made their breakthrough on 15 October they were carrying photographs of eight men as they climbed through from behind the TBM cutterhead. They were remembering and commemorating those who have lost their lives in the course of the huge Gotthard excavation.
But despite the tragedy of such fatalities for families and work colleagues particularly, the Gotthard and its sister Lotschberg base tunnel projects have also coincided with a significant increase in the tunnelling safety culture in Switzerland. New measures were developed specifically because of the extraordinary challenges of this projects and applied on them for the first time, and others have emerged partly because of the experiences made in the work.
“In the 1980s and 1990s tunnelling was part of the general construction risk sector for our insurance,” says Martin Vogel of Suva, a financially independent body dealing with prevention and insurance of accidents and incorporated under public law in Switzerland.
“But the construction industry pressed for separation of the tunnelling risk sector fearing high costs and premiums as the big AlpTransit projects started to gather pace.”
This was done, he says, and the figures for the new sector initially reflected the special risks of underground work. The annual accident frequency was running at more than 400 per thousand employees though it must be added that that figure has to be understood in the light of Swiss practice, which is to report every accident such as a minor scratch.
But the accident frequency in tunneling has been halved in the last 10 years “and is now getting close to the construction industry average,” says Vogel.
US Tariffs are shifting - will you react or anticipate?
Don’t let policy changes catch you off guard. Stay proactive with real-time data and expert analysis.
By GlobalDataA large part of the decrease, and a general improvement of health below ground, reflects a new safety culture developed around the AlpTransit works.
Among the most significant safety measures are diesel particulate filters, a ban on dry mix shotcrete, mandatory rear cameras on plant for reversing and onboard fire extinguishing systems for locomotives and heavy machinery.
Specifically for the base tunnels, new regulations for work under warm and humid conditions have been introduced for tunnels. A temperature limit of 28 degrees C dry temperature was set, along with limits on allowable humidity, which makes work very exhausting. The limits are part of all the contracts, says Vogel.
Much beyond these temperatures it becomes almost impossible to work. A team of Swiss tunnellers, including Suva, visited South Africa in the 1990s while drawing up the safety concepts to assess conditions in shaft sinking and in gold mines.
“There they allow in certain specialized mine workings a maximum of 30.5 degrees C with very high humidity. But the miners for those areas have to pass stringent medicals. It is only about 10 per cent of the workforce.”
The large dimensions of the Swiss tunnel projects and new threshold limits led to an insistence on elimination of diesel particulate exhaust.
“Before, ventilation dilution was used but the air quantities in such long tunnels are not available for this,” says Vogel.
But no adequate filters existed. A special research programme on reduction of diesel-emissions in tunneling was pursued in the 1990s to develop diesel particulate filters, which was finally successful in the late 1990s. Diesel particulate filters are now mandatory in tunnel construction “and the filters are increasingly common on normal cars and trucks in Europe,” says Vogel. They were initially expensive to install, however.
For shotcrete the Swiss industry has traditionally used dry-mix guns that fill the air with cement dust and reduces visibility. The Suva tunnel division drew on Scandinavian experience where wet-mix was introduced earlier. The result is a shift from 90 per cent dry-mix use to 90 per cent wet-mix use not only in Switzerland, but also in Germany and Austria with huge advantages for quality, quantity and health conditions, he says.
Vehicle reversal in tunnels is the greatest source of fatal accidents, he says. Suva introduced mandatory rear cameras on trucks, trains and other machines and he says the incident rate has plunged. Nothing else previously made much impact, he adds. “Audible warnings and bleeps get lost in a tunnel where there is a lot of ambient noise and constant sounds from other equipment.”
Fires, too, are a critical problem for tunnels. “Figures from German mining suggested that we had to expect at least one fire from a locomotive every year,” says Vogel. “That is too high and would create a risk we could not tackle.”
It was decided that locomotives be fitted with fire suppression equipment in the engine compartments and the result has been very successful, he says. In the whole time of the project there have only been few fires on the trains and these were contained.
Fire dangers have also seen other measures introduced. In particular there is a hazard from the heat in the tunnels for rescue crews using rebreathers and normal fire protection clothing. The heavy protection worn by firemen becomes a problem precisely because it is an insulator and causes heat retention, which is compounded by the internal heat generated in the lungs by rebreathing apparatus.
Rescue crews needed special training and other lighter equipment is required. At Sedrun there is a special rescue volunteer forces called “Grubenwehr” drawn from the tunnel crews because the local fire service was not available for that purpose.
Other measures for the industry which have been developing include the notion of the “rescue concept.” Rather than imposing specific measures on a contractor for ensuring tunnel miners can be rescued, this insists on a formalized risk assessment process being undertaken. A fairly long checklist of possible dangers is matched against solutions, with safety measures only having to be taken if a risk is present.
“If a measure is not used this must be declared and a reason given” he says. This flexible method was introduced after examining practice elsewhere he says, such as in Germany “where the rules are strict and detailed but do not give you much scope in finding solutions.”
The major element in rescue provision of rescue chambers in the tunnels with a protected line of air supply and communication to the exterior. They are provisioned with water cooling, emergency air, drinking water and food.
An important issue was that situations should be assessed according to the particular circumstances.
Working on this principle with AlpTransit a number of measures were discussed for example at Sedrun, one of the more difficult project sectors, because it was accessed only by shaft. One issue was the addition of a second access such as a smaller shaft— later enlarged on the contractor’s bid.
“During shaft sinking and excavation of the first cavern safety needed to be able to evacuate the whole shift in one lift in the shaft in the event of flood,” says Vogel.
Suva has also drawn further lessons from incidents on the tunnel, he explains, particularly analysing the fatalities.
Two of these were early during the shaft sinking in Sedrun, one caused by a drilling rod falling 800m because it has been badly fixed when hauled up and the other by a sudden spoil discharge into a kibble during maintenance work. “An air pressurised cylinder for a shutter holding spoil in a chute was released due to a jam from small stone in the mechanism,” says Vogel.
During later tunnelling at Sedrun an accident with the unloading of muck trucks from the shaft hoisting equipment occurred at the shaft top.
At Amsteg there was an accident due to the use of an improvised system to unwind a cable drum which caused the cable drum to slip sideways.
“There was a bad accident fairly early on with the railway muckout at Bodio,” he says. Here a truck bogie in the middle of a train jumped the switch point during a crossover between two parallel tracks and the rear half of the train continued on the wrong track. “A fully loaded truck with a bogie running on each track was pulled like this along the tunnel and killed two people in the way after the collision with a service train.” He says the cause is not certain yet.
There were no fatal accidents in later years, he says, until 2009 when a staff member was killed while guiding a party of visitors. He was caught at the open door of the personnel transportation car by a steel construction with low clearance.
Vogel hopes all of these experiences will feed into other important projects and the whole tunnelling industry, and that despite the tragedy of their occurrence, will help increase standards in an industry now much improved from the past.
“It is worth remembering that on the first Gotthard high tunnel over 100 years ago, there were 177 deaths in driving a tunnel of 15km,” he says. “Even on the Gotthard road tunnel in the 1970s there 17 fatalities on a similar length of 17km.”
Without understating the tragedy now, he says the figure is on another scale, particularly remembering that the length of tunnels driven is 153km in much deeper conditions.
The names of the eight men killed are:
• Andreas Reichardt 23.11.06
• Jacques du Plooy 13.03.01
• Heiko Bujak 03.04.03
• Albert Ginzinger 11.09.03
• Andrea Astorino 21.01.05
• Salvatore Di Benedetto 21.01.05
• Thorsten Elsemann 23.11.06
• Hans Gammel 24.06.09
Tunnelling accidents through the first decade of the 21st century compared to other construction industries Miners carried photos of their eight fallen comrades as they made the final breakthrough
