greatly reduce the probability of death or injury from lightning discharges, they cannot
reduce this probability to zero.
7.3 Lightning warning levels
The EFM measures electric field (efield) from -25,000 to +25,000 V/m. The EFM one-second
measurement of the electric field allows it to detect both cloud-to-ground and cloud-to-cloud
lightning strikes within a 25-mile radius. Lightning strike detection efficiency is 95% when within 5
miles, 93% when within 10 miles, and 68% when within 20 miles.
The optional SG000 measures lightning strikes and their approximate distance broken down into
close (0 to 5 miles), near (0 to 10 miles), or distant (0 to 20 miles).
NOTE:
Lightning safety guidelines based on human observations should not be ignored simply
because of the presence of sensitive electronic instrumentation. The NOAA 30/30 rule
suggests seeking shelter if thunder is heard within 30 seconds of a lightning flash (a distance
of approximately 6 miles), and remaining in a sheltered area for 30 minutes after the last
lightning or thunder before resuming outdoor activities [NOAA].
CS110 Electric Field Meter 16
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