~ National Lightning Safety Institute ~
An Overview of Lightning Detection Equipment
By Richard Kithil, President & CEO, NLSI
Lightning hazards can be mitigated by advanced planning. One part of this safety program may include an early detection and warning alarm package. Lightning detectors can give notice to shut down dangerous operations before the arrival of lightning. They also may signal "all clear" conditions after the lightning threat has passed. Some type of detection package may help you with Duty To Warn issues.
Lightning detectors vary in complexity and cost from large
dedicated equipment packages costing in excess of $150,000 to inexpensive
$20 Radio Shack portable weather radios. The Flash-to-Bang (F-B) Method
requires no dedicated detector: only counting the time in seconds from
seeing lightning’s flash, to seeing the associated thunder or bang. For
each five seconds, lightning is one mile away. Thus, a
F-B of 10 = 2 miles; 15 = 3 miles; 20 = 4 miles; etc.
distances from lightning Strike A to Strike B to Strike C easily can exceed
more than 5 miles. How much time is needed to get to shelter? Suspension
of activities is very site-specific. For most situations, we recommend
activating your lightning defense at a F-B of
30 (lightning is six miles away). We also recommend waiting to resume
activities 30 minutes after the last observed lightning or thunder. This
protocol may seem excessively conservative in many situations…("we'll
never get anything done under such strict guidelines…"). It is a case-by-case risk management decision.
And yes, safety and productivity sometimes are mutually incompatible.
Safety, however, always should be the prevailing directive.
Available technologies of the present day lightning detectors
a. Radio Frequency (RF) Detectors. These measure energy discharges from lightning. They can determine the approximate distance and direction of the threat.
b. Inferometers. These are multi-station devices, much more costly than RF detectors. They measure lightning strike data more precisely. Usually they require a skilled operator.
c. NLDN. The National Lightning Detection Network covers all the USA/Canada and reports lightning strikes to a central station. Local storm data is available by subscription. Past strike information is archived and accessible upon request.
d. Atmospheric Field Mill Monitors. These measure the potential gradient (voltage) changes of the earth's electric field and report changes as thresholds build to lightning breakdown values.
e. e. Optical Monitors. These can provide earlier warning as they detect cloud-to- cloud lightning that typically precedes cloud-to-ground lightning.
f. Hybrid Designs. These monitors use a combination of the other single-technology designs. Two or more sources of information may be better than just one.
Subscription Services. NLSI Recommendation
- Rent a Meteorologist. Here hired professionals make the critical decisions
and advise you. This method may blunt claims
of Negligence if something goes wrong. Off-site detection-by-subscription
is available from several capable vendors, including: Accuweather.com;
Intellicast.com; Lightningstorm.com; and, Skyview-wx.com.
Beware of a false sense of confidence from detectors: none
of them will detect all of the lightning all of the time. None of them
will provide "first strike/Bolt Out of the Blue" information
or forecast in advance the positions of lightning strikes on earth. Various
detector detection receiver algorythms operate at different frequencies
and wavelengths: Boltek Stormtracker in the Low Frequency Range 100-700
KHZ?; Vaisala GAI NLDN
at 100-400 KHZ; NMT Lightning Array at VHF 60-78 MHZ; LIS
and OTD optical at 777.4 m; Vaisala SAFIR VHF 109-119 MHZ; Vaisala GAI
LDAR II at 50-120 MHZ; GAI VLF at 20-50 KHZ; the UK Meteorological Office
RDI at 9.8 KHZ; etc. An excellent summary of families of lightning detectors
is at: http://thunder.msfc.nasa.gov/validation/instruments.html
Detectors can display early warning of lightning conditions
to explosives operations. A signaling or alarm notification method is
essential to alert field personnel of these dangerous circumstances. Two-way
radios, remote sirens, strobe lights and other methods are available.
Essential companions to any type lightning detector include:
1) A written
Lightning Safety Policy; 2) Designation of Primary Safety Person; 3) Determination
of when to suspend activities; 4) Determination of Safe/Not Safe Shelters;
5) Notification to Persons at Risk; 6) Education: at a minimum consider
posting information about lightning and your organization’s safety program;
7) Determination of when to resume activities.
Understand the equipment’s limitations in the face of the
capricious behavior of lightning. Even Total Lightning Information (TLI)
as employed by strategic military meteorologists works on assumptions.
[TLI = a combination of synoptic charts; modeling output statistics; local
and upper air soundings; regional radar; NLDN et al; satellite interpretation;
current synoptic situation; discussions within authorities; experience;
Select the detector and/or signaling device that is site-specific to your requirements, easiest to use, and which offers the most favorable cost/benefit to your operation’s budget.