SEA/Specific/TBT-SEA-011

Thunderstorm Safety Protocol

Seasonal & Weather › Specific › Thunderstorm Safety Protocol

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Lightning strikes kill and seriously injure construction workers exposed on open sites every year.
Workers at height on scaffolds, cranes, steel frames, and roof structures are most at risk.
The 30/30 rule: if lightning follows thunder by less than 30 seconds, seek shelter immediately.
Metal structures, cranes, and equipment attract lightning and conduct the strike to ground level.
Workers holding metal tools, survey poles, or scaffolding tubes become part of the lightning path.
Ground current from a nearby lightning strike can electrocute workers standing on wet ground.
Work at height, crane operations, and external scaffolding must stop when thunderstorms approach.
The 30-minute rule: wait at least 30 minutes after the last thunder before resuming outdoor work.
Lightning can strike from a storm several miles away; blue sky overhead does not mean safety.
A site-specific thunderstorm protocol should define trigger points, shelter locations, and resumption criteria.

Fatal strikes	Lightning delivers up to 300 million volts. Direct and indirect strikes cause cardiac arrest, burns, and death.
Height exposure	Workers on scaffolds, cranes, and steel frames are the highest points on site, attracting lightning directly.
Ground current	Lightning striking the ground spreads current that electrocutes workers standing nearby on wet or conductive surfaces.

Don't

Monitor weather forecasts for thunderstorm warnings before and during each shift.
Stop all work at height and crane operations when thunderstorms approach the site.
Apply the 30/30 rule: shelter if thunder follows lightning by less than 30 seconds.
Shelter in substantial buildings or enclosed vehicles, not under trees or open structures.
Wait at least 30 minutes after the last thunder before resuming outdoor work.
Put down metal tools, survey poles, and scaffolding tubes when seeking shelter.
Descend from scaffolds, steel frames, and elevated positions as storms approach.
Avoid standing near metal fences, plant, or tall isolated structures during storms.
Brief the team on shelter locations and the thunderstorm stop-work procedure.
Crouch low with feet together if caught in the open with no shelter available.

DON'T continue working at height when thunderstorms are within 10 miles of site.
DON'T shelter under trees, scaffolds, or open-sided structures during lightning.
DON'T hold metal tools, poles, or scaffolding tubes when lightning is nearby.
DON'T resume work until 30 minutes after the last thunder is heard.
DON'T assume the storm has passed because rain stops; lightning can persist.
DON'T lie flat on the ground during a storm; crouch low with feet together.
DON'T remain in or on crane cabs during thunderstorms; descend to ground level.
DON'T stand on wet ground near tall metal structures when lightning is active.
DON'T use mobile phones or radios in exposed positions during active lightning.
DON'T ignore distant thunder; storms move quickly and lightning reaches far ahead.

See also: Working in High Winds | Lightning Strike Procedures

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