If the events of 11 September 2001 taught me about the usefulness of email, the US power cuts of last week showed me its limitations.

After the attack on the World Trade Centre, the New York phone system was paralysed, and the only way to make sure my New York friends were OK was via email.

But last week, after the power cuts, it was well into the weekend before some folks got back online.

New York has been something of a disaster recovery test bed over the last couple of years. But by studying their experiences we can learn a lot.

Among the key winners were the internet domain name system (DNS) servers. Apart from some sites slowing down due to heavy traffic, the bulk of the traffic carried on as normal.

DNS systems that were hit by power loss didn't fail, because those running them made sure that they had back-up generators with three days' worth of fuel to hand.

Wall Street also came off well: most brokerage houses had back-up power and were open for business as usual on Friday.

But the 'loser' category turned out to include pretty much everyone else. Bank machines couldn't dispense money, the mobile phone network fell over when most of the masts failed, and one poor woman was stuck alone in an elevator that no one thought to check for over 19 hours.

Restaurants lost thousands of dollars in spoiled food and overheated wines as temperatures soared. Traffic ground to a halt as traffic lights failed and people took to the streets to walk home.

And don't think it couldn't happen here. Wide area power outages could become more common in this country as we lose our self-sufficiency with fuels like gas, and begin to rely more on overseas power sources, mainly from eastern Europe.

The UK only holds 48 hours' worth of back-up fuel for gas power stations and, as the fuel pipe attacks in Iraq showed, terrorists have got smart to hitting infrastructure targets for maximum disruption.

So much of disaster planning is to do with IT, and rightly so. But it's time to start looking at the bigger picture.

If the lights do go down do you have a checklist prepared to make sure everyone is out of the building?

Will your electronic locks function? Are your staff briefed on shutting down lights and electronic devices to avoid an overload when the power comes back on?

Only by preparing for the worst can we ensure the best result.