User Tools

Site Tools


australia:lightning_safety

how to reduce your risks in lightning storms

see also:

  • most lightning injuries occur on the outskirts of storms when there is little rain rather when they are overhead as most people do seek shelter when the rain is very heavy
  • the safest place in lightning is to be indoors - and not holding a copper wired phone
  • the net safest place is sitting in a car without touching the exterior which acts as a Faraday cage
  • in Australia, 10 people die each year and some 100 are injured from lightning strikes
  • in hot weather conditions, lightning can start bushfires which can spread rapidly and trap hikers - avoid hiking in extreme bushfire danger periods

introduction

  • sound travels about 1 mile in 5 seconds
  • if you hear thunder and no lightning seen yet:
    • secure outdoor equipment
    • cease outdoor activity
    • plan your shelter at a low risk site (see below) and strongly consider remaining there
  • if the gap between lightning and thunder is less than 30secs
    • urgently seek shelter if no suitable shelter then adopt lightning position (see below)
    • then wait there 30 minutes until after last thunder
  • if you feel your hairs on end, a strike is imminent within seconds, immediately adopt lightning position

lightning injuries

  • most lightning injuries come from indirect effects of a nearby lightning strike:
    • ground conducted step potential
      • current spreads across the ground from the strike zone
      • the further apart your feet, the greater the voltage differential between them and the more current to your heart
      • most likely occurs when lightning hits a nearby structure such as a hut or tree
      • accounts for 50-70% of injuries
    • flashover hazard
      • as current develops in a tree hit by lightning, a voltage differential develops and if this exceeds the air breakdown value to a nearby person, that person becomes part of the current (don't be touching the tree or be within 2m of it)
      • this can also occur indoors if you use or are nearby a landline phone which carries lightning current from a nearby strike
    • shrapnel or falling branches
      • lightning hitting a tree may cause it to explode sending dangerous shrapnel flying

Check out the blast shrapnel and falling branches (image courtesy of gizmodo)

find a lower risk site

  • highest risks are:
    • within 5m of a tall object such as an antenna, isolated tree, pavilion, bus stop, etc
    • on a hilltop (doubles your chances of strike compared to open paddock)
    • on an open paddock
    • holding a metal or carbon fibre object such as a tent pole, wire fence, umbrella, tripod, fishing rod, golf club
    • in water eg. swimming or boating
      • if you are stuck in a boat, go below deck if possible
    • sites where lightning strikes frequently (note past lightning strikes of trees)
    • in a tent in any of the above sites
      • if your tent is in a high risk position, leave the tent and find a safer location
  • lower your risk by:
    • get inside a car or lightning shelter
      • cars are much safer than tents as they act like Faraday cages while tent poles, whether aluminium or carbon fibre act like lightning rods
      • there are several ways a shelter can be protected, but if metal wire is to be used it must be at least 1/4“ steel cable and several metres higher than the shelter, and be grounded properly at each end to avoid flashover hazard
    • grove of trees (reduces your strike probability to 25% compared to an open paddock)
    • be within distance of 3 x height of a taller object but further than 5m away and protected from any potential shrapnel although protection is best in the zone within the height of the object
      • tall trees do offer an alternative path for lightning strikes if you are within a distance 3 x height of the tree but as long as you are at least 5m away to avoid the corona of the strike, significant ground currents and shrapnel as it explodes from the strike, so ideally if you pitch your tent 10-15m away from a 30m tree theoretically, the tree may be protective - as long as it doesn't fall down in your direction or you are standing in wet ground or you get hit by shrapnel.

pitch your tent assuming there may be a storm overnight

  • avoid watercourses which may flood
  • avoid being under trees with large branches which may drop without warning
    • Australian eucalypt trees often drop large branches without warning even without wind or storms as a way of surviving drought or fungal disease - these kill campers and farmers although deaths are rare
    • higher risk:
      • horizontal branches
      • species susceptible to “Sudden Branch Drop (SBD)” include yellow box, maiden's blue gum, mountain ash and river red gum
      • trees exuding dark sap which suggests infection by tree rot
      • late afternoon or early morning in dry spells or droughts
      • older trees
  • avoid hilltops and exposed ridges no matter how nice the views
  • avoid open paddocks
  • avoid other high risk lightning sites such as next to an isolated tree or pole

the lightning position

  • be on the driest soil and if possible select a low risk site
  • stay away from metal objects such as cooking appliances, backpack, wire fences, tent poles, etc
  • if there is time, remove metal objects such as belt buckles, etc
  • have each person about 15m apart to avoid group injuries
  • hopefully you are wearing rubber soles, although these are only protective for perhaps 5000V - no match for a 100,000V direct strike!
  • preferably have an insulating, dry plastic sheet or pad to crouch on to reduce impact of ground current
  • crouch with ankles together to keep the current ankle to ankle rather than up the body and down back to earth
  • squat down, sitting on the heels of your feet with the balls and toes of your feet touching the ground to lower your height
  • tuck your head down to your knees to minimize chance of a strike on the head and give lightning that does hit you a path down your back to ground - your chances of survival are greater
  • try to hold this position for the hour that the storm takes to pass through
  • hands over ears to prevent ear drums blowing out
  • close eyes to prevent blindness

first aid

  • as there is no ongoing current after a strike, there is no danger from electrocution in attending a lightning strike victim (other than from a subsequent lightning strike), and indeed, if they are unresponsive and in cardiac arrest from current passing through their heart, their only hope of survival is first aid for management of cardiac arrest and ventricular fibrillation which involves immediate CPR and early defibrillation
australia/lightning_safety.txt · Last modified: 2017/12/16 00:45 by gary1