LEADING ARTICLE : Dangerous days in commuterland

Imagine yourself travelling to work yesterday on the Tokyo subway. You are minding your own business, trying to maintain a little personal space. Your greatest concern is a bronchitic passenger coughing germs everywhere. Then, suddenly, those beside you are overcome by fumes. Passengers collapse, foaming at the mouth, bleeding from the nose, vomiting. There is no way of quickly escaping the unknown, odourless, colourless killer.

Yesterday's atrocity in Tokyo combines some of our worst fears: confined spaces, random killing and the vulnerability of an apparently orderly society to the subversion of a few. Mass murders of the conventional type are horrific enough. Supermarket mall shootings in the United States and the Hungerford massacre here in 1987 have made such atrocities part of real life. But at least in these incidents, the victims could see someone firing a gun. They may have felt that they had a chance to avoid the carnage, if only by pretending to be dead. In Tokyo, victims were picked indiscriminately and had no way of protecting themselves. Vigilance is almost impossible against a substance you can neither see nor smell.

Death by gas has a resonance that is not shared by any other killing device, except perhaps nuclear weapons. Somehow we can accept death, however, painful, by the bullet or the bomb. Gas is special. It evokes memories of crocodile lines of soldiers blinded in the First World War by mustard gas and of the millions killed in Nazi concentration camps. We are so fearful of poisonous gas that it is virtually the only killing device which most countries would be prepared to ban. The 1993 Chemical Weapons Convention, which Britain has yet to ratify, makes it illegal not only to use such weapons, but also to develop, produce and stockpile them.

Yet, even if that ban was applied by all states, it would not have saved those who died or were injured yesterday. There is no realistic way to ensure that passengers on a public transport system are safe from terrorists with access to kitchen chemistry. A similar outrage could take place here.

The main reason such atrocities have not occurred before is because no one has been prepared to commit them. Our insurance against a repeat of yesterday's events is that most terrorists do not descend to such depths of inhumanity. Today, anyone taking a bus or a train or visiting a public place may be more aware of how vulnerable we are to the madness of fellow citizens.