When airports across Europe reopened after the closure caused by the eruption of Iceland’s Eyjafjallajökull volcano, it was not because the amount of ash in the atmosphere had dropped, but because the risk that the ash posed to airplane safety had been reassessed.

Was it new scientific information that led to the lifting of the flight ban, or was it a reflection of the hardship, both personal and economic, that the ban was causing?

Over six days, about 95,000 flights were canceled, at a cost to airlines of more than $1 billion. An estimated five million people were stranded or delayed.

The British economy lost £1.5 billion, and others were similarly affected. Flower growers in Kenya, who depend on air transport to take their short-lived product to Europe, suddenly had no income.

Sixteen cancer patients in critical need of bone marrow for transplants were put at risk because the matching marrow could not be flown in from the United States or Canada.
In the past, jets flying into ash from volcanoes in the US, Indonesia, the Philippines, and Mexico have temporarily lost engine power, and in one case, dropped thousands of feet, although all managed to land safely.

But there was no evidence that the more widely dispersed ash blowing over Europe from Iceland would cause similar problems. The decision to ground flights was based on the view that any level of ash in the atmosphere posed some risk to aircraft, and that no matter how slight that risk might be, the government’s job was, as British Prime Minister Gordon Brown put it, "to make sure that safety was paramount.”

Indeed, in closing their skies, European governments seem to have given safety absolute priority over everything else. Yet none of them act on that principle in other areas. Some 3,000 people die on the world’s roads every day.

Cutting speed limits to, say, 10 kilometers per hour would prevent most accidents and save many lives. We don’t do it, because we give safety a lower priority than our desire to spend less time driving.

The price we are willing to pay for safety cannot be infinite. It is distasteful to put a price on human life, but the more we spend on safety, the less we will have for our other goals.

The British government uses a figure of a little more than £1 million as a general limit to the amount it is prepared to pay to save a statistical life – for example, by improving road safety. In the US, the Department of Transportation is prepared to go up to $5.8 million – nearly four times as much, at current exchange rates – for the same purpose. Does that mean that safety is paramount in the US, but not in Britain?

Giovanni Bisignani, the head of the International Air Transport Association, an industry group, criticized the shutdown, saying that no risk assessment had been undertaken. On the whole, though, the public seemed to support the decision.

Stranded travelers, interviewed at airports, typically said that they would rather be stuck at an airport than in a plane falling out of the sky.

But what if some travelers have a higher tolerance of risk, or just a more urgent need to travel, than others? John Stuart Mill, in his classic book On Liberty, considered a situation in which a man sets out to cross a bridge that we know is unsafe.

In Mill’s view, we are justified in stopping him only to make sure that he is aware of the danger. Once he knows of it, the decision is his to make, because only he can judge the importance of his journey, and balance that against the risk he is running.

Air safety is slightly different, because a crashing plane can kill people on the ground, but the greatest risks by far are borne by the passengers and crew.

If they are fully informed of the risks, and are still willing to fly – perhaps the crew has been offered more money, as workers in dangerous occupations often are – should we prevent them from making the decision to fly?

In the end, after test flights with no passengers aboard had shown no engine damage, and aircraft engine manufacturers told aviation authorities that their engines could operate safely with a low level of ash in the atmosphere, Europe’s skies were reopened.

The International Civil Aviation Authority has announced that it will convene a group of experts to help it provide guidance for the industry to decide what level of ash in the atmosphere makes it unsafe to fly.  

Now that we have seen the costs of giving absolute priority to safety, we know that this is not only a technical question. I trust that among the experts will be some who have pondered the underlying ethical question: how safe should we aim to be?

Peter Singer is Professor of Bioethics at Princeton University and Laureate Professor at the University of Melbourne.

Copyright: Project Syndicate, 2010.