Lightning service

Rapid data about electrical storms will help to control damage

LIGHTNING never strikes twice in the same place, they say. But your chances of being hit just the once are far greater in the East Midlands than the Thames Valley. In 1994, there were five strikes per square kilometre in the East Midlands, compared with 0.5 per square kilometre in the Thames Valley.

This finding, along with other statistics on lightning strikes, will form the basis of a new version of British Standard 6651 Protection of Structures Against Lightning due to be published next year.

The statistics come from a national lightning location system that is so fast that users can see lightning data displayed on screen before the thunder is heard. Comprehensive information on the number of lightning strikes occurring during thunderstorms anywhere in the UK and the Irish Republic, their time, location and the energy dissipated in each strike, is automatically collected and analysed by the system. It was developed by EA Technology to help the electricity industry monitor lightning damage to power lines. Data from the system showed that the current version of BS6651, based on information collected in the US, did not reflect the risk in Britain.

Formerly the research arm of the Central Electricity Generating Board, EA Technology is now independent, and keen to develop new markets for the lightning information in other sectors such as telecommunications, civil and military aviation, petrochemicals and insurance.

BT and the Irish telecommunications company, Telcom Eirean, are both users. Some insurance companies are using historical data to check claims, and because the system makes it possible to map variations in lightning frequency from one area to another, it could also be used for risk assessment.

It is known that in general the east of the country experiences more lightning than the west, but there are also wide variations from year to year within regions: although the East Midlands had five strikes per square kilometre in 1994, it had an average of two strikes per square kilometre in the five years from 1989.

Six direction-finding aerials around Britain locate lightning strikes as they occur by picking up radio waves. The information is sent to the central computer at EA Technology's offices in Chester, and within seconds of the strike occurring it is marked on the map and relayed to on-line subcribers. For example, a storm in southern England on 24 and 25 June, 1994, contained more than 85,000 cloud-to-ground strikes, each averaging 15 amps. The system is capable of recording up to 100 strikes per second.

"In the UK, most people will witness only one or two major storms a year, and seldom, if ever, see any damage," said Mike Lees, at EA Technology. "We therefore tend to dismiss lightning as an acceptable risk." In fact, direct lightning strikes can devastate trees and buildings and cause widespread disruption to power and telecommunications.

The last national survey of lightning damage to the electricity industry, carried out before privatisation, put the annual cost at £4m. Of course, monitoring lightning does not stop the damage, but it can cut the cost of putting it right. If a power line goes down during a storm, knowing where the lightning occurred helps to locate the fault more quickly.

Companies are able to judge as and when the lightning starts and whether they need to reconfigure networks or put expensive extra capacity on standby. Previously, they had to rely on far less specific Meteorological Office forecasts and thus needed to take more elaborate and costly precautions.

The Met Office is about to start using the location service to assess the accuracy of its forecasts. It hopes the feedback will improve its forecasting. EA Technology is now planning to make the system predictive, by tracking storms as they come in from over the Atlantic. Mr Lees said this will make it possible to provide very accurate lightning warnings two hours in advance.