The proactive plan should commence on the day before activity, where weather forecasts provide important warning of possible thunderstorm activity.8 Increased awareness of lightning risk should continue on the day of activity until play has finished and the crowd has dispersed.

The most basic level of warning involves observation of the weather in the local area. The first flash of lightning or clap of thunder, no matter how far away, should heighten lightning-awareness. The level of risk depends to a large degree on one's location relative to the storm system, which can be determined by the "flash-to-bang" rule (see below). Further useful information can be obtained by liaison with the Bureau of Meteorology <http://www.bom.gov.au>.

In recent years, major advances have been made in technology for identifying and locating lightning. In Australia, there is a network of sensors that enable cloud-to-ground flashes to be mapped to within a few hundred metres. Together with other details about local weather conditions, the Lightning Location System can provide real-time displays of lightning strikes and determine the speed and direction of movement of the thunderstorm. This information can be used to estimate the likely future path of the thunderstorms and their probable arrival times at various venues.

During the formulation of specific lightning safety guidelines, a specific person should be given responsibility for monitoring the weather for signs of a developing thunderstorm. The nominated "weather watcher" should have the authority to postpone the event and have competitors, officials and spectators moved to safe areas. Appropriate people to nominate as weather watchers include the event supervisor, trainers or other medical personnel, or the ground manager.

When lightning threatens, the weather watcher is responsible for recognising the danger and activating the lightning protection plan. This should include a signal to the referees and umpires, as well as a method of informing those at risk (ie, players, officials and spectators) of the action required.

No place is absolutely safe from the lightning threat; however, some places are safer than others (Box 1).1,12

It is important to have already identified safe structures and the most appropriate way of moving people into these facilities. The best choice is a large, fully enclosed building.

The "30/30" rule is recommended for lightning safety and serves as a guide for the suspension and subsequent resumption of activity.7,13

The first part of this rule (a flash-to-bang count of 30 s) is a guide to the suspension of activity. The flash-to-bang count is one of the most practical techniques for estimating the distance to lightning activity. It is based on the fact that light travels faster than sound. Given that sound travels at a speed of about one kilometre every three seconds, the time that elapses between the flash of lightning and clap of thunder can be divided by three to give a measure of how far away the storm is in kilometres.8,14

The overall message is to seek shelter when the lightning activity is too close, but how do we define what is meant by too close? Currently, most experts agree that the accepted "safe" distance is no less than 10 km.1,7-10,15 This means that as the flash-to-bang count approaches 30 seconds, all people at risk should be seeking or already inside safe shelters.

The second part of the 30/30 rule provides the criteria for resumption of play. Here it is recommended that people wait 30 minutes after the last sight of lightning or sound of thunder. This figure is based on the observation that a typical storm moves at about 40 km/h. Thus, waiting 30 minutes allows the thunderstorm to be about 20 km away, minimising the probability of a nearby strike. It is important to emphasise that blue skies and lack of rainfall are not adequate reasons to breach the 30-minute return-to-play rule.1,7,9

It is important that all participants, officials and spectators are warned of the potential dangers of lightning and how to minimise their risk of lightning-related injury. Practical ways in which this can be achieved include:

• reading lightning safety messages over the public address systems; and

• placing notices and safety instructions in event programs and in high-traffic areas at each venue (eg, entrance, change rooms, clubhouse).

The information should contain clear and specific instructions about:

• criteria for suspension and resumption of athletic and recreational activities; and

• locations of the safety shelters and the best way to access them, as well as suitable alternative shelters.

It is important to have a back-up plan in the case of power or equipment failure.