Several of the more proactive passengers found the emergency buttons on either side of the carriage.

Let me pause here to describe the subway's notion of an 'emergency button'. Not only is it small enough to inspire mirth, but it is actually the exact brand and model of the household light switch I have in my living room. I flicked the switch up and down, several times. Nothing. No alarm. No slowing of the train. No voice of authority over the loudspeaker. A passenger on the other side of the car flicked the other switch. Again, nothing.

Farcically, neither switch is connected to anything. Perhaps they are just there to give the victims of accidents or terrorism something to do before they pass out and die. In all seriousness, it was at this point that my fear and panic acquired a hue of sadness. Oddly enough, my own life did not flash before my eyes. It was the lives of others who had died in enclosed spaces, cut off from the world, that coloured my consciousness.

Sometime during the next helpless minute or so, the toxic cloud subsided. We were safe, but far from happy.

Obviously, this was not a terrorist act. Otherwise, we would all have been dead, and no one would have known until the train rolled blithely into Dazhongsi station, full of several hundred corpses. It was apparent that we had endured some airborne substance from outside the train or - worse - something produced by the train itself.

Cold comfort indeed. Regardless of what chemical concoction had been visited upon my lungs and brain, neither its origin nor intent concerned me. Airborne toxins entering a sealed, moving subway carriage constitutes an emergency. A few minutes later, I disembarked at Dazhongsi station, my clothes still seeped in whatever toxic cocktail had infiltrated the car. I took the name and phone number of another passenger as a witness to the event. But not a single other person got off to make a fuss.

I marched straight to the station offices, populated by uniformed people with nicely coloured badges. After quickly debriefing them, I asked to speak to a person or department responsible for subway safety.

My interlocutors might as well have been from another planet. None of the staff, including the managing director, knew who was in charge of safety for the subway.

Apparently, the placebo emergency buttons are not the only problem.

One of the nonplussed staff asked me if there was a phone in the carriage. 'If you're asking me, then what's your job?' I said. I did not see a phone. I hope there is one, but I'm never going back to find out. And had this been a real attack, it would not have mattered: in the panic of the moment, a dozen of us went for the red herrings, the two non-functioning 'emergency buttons'.

'We'll pass word on to our superiors,' said the station manager. I told him, unsubtly, that he was missing the point. Nevertheless, he failed to find anything I had just told him very interesting or worthy of further investigation. No report to fill out. No detailed questions. Nothing.

When, after five more minutes, the staff could still not locate anyone responsible for safety, I suggested that they should, perhaps, call the information helpline.

After some hesitation, I have decided that it is vital to report that the subway authority for a metropolis of 13 million people - and the host of the 2008 Olympics - does not appear to have a risk-management system.

And if it does, then those responsible for its implementation should find another line of work. Beijing's subway system is one big death trap - not just a terrorist's playground, but a banal tragedy waiting to take its sad place in world headlines.

Christopher Barden is a screenwriter living in Beijing