Excerpts from the Bulletin of the American Meteorological Society: Vol.
80, No. 10, pp. 2035-2041 (October 1999 issue, full
text).
Updated recommendations for lightning safety
1998 Ronald L. Holle and Raúl E. López (National Severe Storms Laboratory,
NOAA Norman, Oklahoma)
Christoph Zimmermann (Global Atmospherics, Inc. Tucson, Arizona)
1. Introduction
Meteorological agencies in the United States and around the world issue warnings,
statements, and other forecasts with the goal of mitigating casualties and
damages caused by severe weather. These products are issued for three of the
four important causes of storm-related fatalities-floods, tornadoes, and hurricanes
(Figure 1). However, no warnings or forecasts are typically issued for lightning,
which is reported by the NOAA publication Storm Data to rank second to floods
in the number of deaths. Lightning also injures at least 300 people each year
in the U.S. After taking into account the underreporting of lightning deaths
and injuries (López et al. 1993), about 100 people are estimated to be
killed and more than 500 injured by lightning in the U.S. each year. Cherington
et al. (1999) found that when emergency-room visits were included, a ratio
of 10 lightning injuries to one death applied in Colorado.
The magnitude of the cloud-to-ground lightning hazard is understood better
today than had been the case due in large part to data collected by the U.S.
National Lightning Detection NetworkTM (NLDN) described by Holle and López
(1994) and Cummins et al. (1998). From 1992 to 1995, the NLDN identified an
average of 21,746,000 cloud-to-ground flashes per year (Orville and Silver
1997). Lightning occurs in the U.S. every day in summer, and nearly every day
during the rest of the year. Since lightning strikes the ground in such large
numbers and is so widespread, it is not possible to warn each person for every
flash. For this reason, lightning can be considered the most dangerous weather
hazard that many people encounter each year. Lightning-specific warnings have
proven effective in some unique applications, such as at the Kennedy Space
Center and during major golf tournaments.
Although the scientific understanding of lightning has advanced significantly
in the last few decades (Krider 1996), a consistent match between basic science
and applications to safety had not been made. For example, NOAA (1992) said
to squat on the balls of your feet and minimize contact with the ground, while
NOAA (1985) recommended dropping to the knees during the lightning threat,
and NOAA (1970) suggested dropping to the ground. Concerning when to reach
a safe location, NOAA (1992) recommended going to a safe location at the first
sound of thunder, NOAA (1985) was not specific about when to go to a safe place,
and NOAA (1970) made no mention of this decision process. Similar variations
can be found in these and many other publications regarding additional issues
such as medical and first aid approaches to lightning victims.
In response to inconsistent safety recommendations and recent findings concerning
the lightning phenomenon, a Lightning Safety Group (LSG) met informally during
the American Meteorological Society's Annual Meeting in Phoenix in January
1998. The LSG was comprised of people who were known to be active in lightning
safety and education issues, but by no means was complete. Attendees were involved
in developing warning methods, giving lightning safety presentations to groups,
seeing patients who were lightning casualties, conducting research into the
epidemiology of lightning victims, and/or developing policies for lightning
safety. Individuals who were able to attend the meeting are listed in Table
1. Also included are people who are active in these lightning safety and education
issues, but unable to attend.
The following summarizes recommendations adopted during the AMS Annual Meeting
and in subsequent drafts circulated from January to May 1998. The LSG internally
agreed upon this text during the process, but it was not reviewed externally.
Only the references were added to the following consensus text. The recommendations
are being circulated now for general information and to stimulate further comments
and discussion from readers of the AMS Bulletin.
2. The recommendations
- Abstract
On average, lightning causes more casualties annually in the US than any
other storm related phenomena, except floods. Many people incur injuries
or are killed due to misinformation and inappropriate behavior during thunderstorms.
A few simple precautions can reduce many of the dangers posed by lightning.
In order to standardize recommended actions during thunderstorms, a group
of qualified experts from various backgrounds collectively have addressed
personal safety in regard to lightning, based on recently improved understanding
of thunderstorm behavior. This "Lightning Safety Group" (LSG) first convened
during the 1998 American Meteorological Society Conference in Phoenix,
Arizona to outline appropriate actions under various circumstances when
lightning threatens.
- Key conclusions
The seemingly random nature of thunderstorms cannot guarantee the individual
or group absolute protection from lightning strikes, however, being aware
of, and following proven lightning safety guidelines can greatly reduce
the risk of injury or death. The individual is ultimately responsible for
his/her personal safety and has the right to take appropriate action when
threatened by lightning. Adults must take responsibility for the safety
of children in their care during thunderstorm activity.
- Safer locations during thunderstorms and locations to avoid
- No place is absolutely safe from the lightning threat, however, some
places are safer than others.
- Large enclosed structures (substantially constructed buildings) tend
to be much safer than smaller or open structures. The risk for lightning
injury depends on whether the structure incorporates lightning protection,
construction materials used, and the size of the structure (see NFPA
780, Appendix E & H).
- In general, fully enclosed metal vehicles such as cars, trucks, buses,
vans, fully enclosed farm vehicles, etc. with the windows rolled up
provide good shelter from lightning. Avoid contact with metal or conducting
surfaces outside or inside the vehicle.
- AVOID being in or near high places and open fields, isolated trees,
unprotected gazebos, rain or picnic shelters, baseball dugouts, communications
towers, flagpoles, light poles, bleachers (metal or wood), metal fences,
convertibles, golf carts, water (ocean, lakes, swimming pools, rivers,
etc.).
- When inside a building AVOID use of the telephone, taking a shower,
washing your hands, doing dishes, or any contact with conductive surfaces
with exposure to the outside such as metal door or window frames, electrical
wiring, telephone wiring, cable TV wiring, plumbing, etc.
- Safety guidelines for individuals
- Generally speaking, if an individual can see lightning and/or hear thunder
he/she is already at risk. Louder or more frequent thunder indicates that
lightning activity is approaching, increasing the risk for lightning injury
or death. If the time delay between seeing the flash (lightning) and hearing
the bang (thunder) is less than 30 seconds, the individual should be in,
or seek a safer location (see Safer Locations during Thunderstorms and
Locations to Avoid). Be aware that this method of ranging has severe limitations
in part due to the difficulty of associating the proper thunder to the
corresponding flash.
- High winds, rainfall, and cloud cover often act as precursors to actual
cloud-to-ground strikes notifying individuals to take action. Many lightning
casualties occur in the beginning, as the storm approaches, because people
ignore these precursors. Also, many lightning casualties occur after the
perceived threat has passed. Generally, the lightning threat diminishes
with time after the last sound of thunder, but may persist for more than
30 minutes. When thunderstorms are in the area but not overhead, the lightning
threat can exist even when it is sunny, not raining, or when clear sky
is visible.
- When available, pay attention to weather warning devices such as NOAA
weather radio and/or credible lightning detection systems, however, do
not let this information override good common sense.
- Considerations for small groups and/or when the evacuation time is
less than ten minutes
- An action plan must be known in advance by all persons involved (see
Important Components to an Action Plan, P.5). School teachers, camp
counselors, lifeguards, and other adults must take responsibility for
the safety of children in their care.
- Local weather forecasts, NOAA weather radio, or the Weather Channel
should be monitored prior to the outdoor event to ascertain if thunderstorms
are in the forecast. Designate a responsible person to monitor forecasted
weather as well as to observe on-site developments to keep everyone
informed when potential threats develop.
- Recognize that personal observation of lightning may not be sufficient;
additional information such as a lightning detection system or additional
weather information may be required to ensure consistency, accuracy,
and adequate advance warning.
- Even though technology and instrumentation have proven to be effective,
they cannot guarantee safety. Instrumentation can be used to enhance
warning during the initial stages of the storm by detecting lightning
in relation to the area of concern. Advance notification of the storm's
arrival should be used to provide additional time to seek safety. Detectors
are also a valuable tool to determine the "All Clear" (last occurrence
of lightning within a specified range), providing a time reference
for safe resumption of activities.
- Considerations for large groups and/or when the evacuation time is
more than ten minutes
- An action plan must be known in advance by all persons involved (see
Important Components to an Action Plan). Adults must take responsibility
for the safety of children in their care.
- Local weather forecasts, NOAA weather radio, or the Weather Channel
should be monitored prior to the outdoor event to ascertain if thunderstorms
are in the forecast. During the event, a designated responsible person
should monitor site relative weather condition changes.
- Personal observation of the lightning threat is not adequate; additional
information including detecting actual lightning strikes and monitoring
the range at which they are occurring relative to the activity is required
to ensure consistency, accuracy, and adequate advance warning.
- Even though technology and instrumentation have proven to be effective,
they cannot guarantee safety. Instrumentation can be used to enhance
warning during the initial stages of the storm by detecting lightning
in relation to the area of concern. Advance notification of the storm's
arrival should be used to provide additional time to seek safety. Detectors
are also a valuable tool to determine the "All Clear" (last occurrence
of lightning within a specified range), providing a time reference
for safe resumption of activities.
- When larger groups are involved the time needed to properly evacuate
an area increases. As time requirements change, the distance at which
lightning is noted and considered a threat to move into the area must
be increased. Extending the range used to determine threat potential
also increases the chance that a localized cell or thunderstorm may
not reach the area giving the impression of a "false alarm".
- Remember, lightning is always generated and connected to a thundercloud
but may strike many miles from the edge of the thunderstorm cell. Acceptable
downtime (time of alert state) has to be balanced with the risk posed
by lightning. Accepting responsibility for larger groups of people
requires more sophistication and diligence to assure that all possibilities
are considered.
- Important components of an action plan
- Management, event coordinators, organizations, and groups should
designate a responsible, person(s) to monitor the weather to initiate
the evacuation process when appropriate. Monitoring should begin days
and even hours ahead of an event.
- A protocol needs to be in place to notify all persons at risk from
the lightning threat. Depending on the number of individuals involved,
a team of people may be needed to coordinate the evacuation plan. Adults
must take responsibility for the safety of children in their care.
- Safer sites must be identified beforehand, along with a means to
route the people to those locations. School buses are an excellent
lightning shelter that can be provided (strategically placed around
various locations) by organizers of outdoor events, with larger groups
of people and larger areas, such as golf tournaments, summer day camps,
swim meets, military training, scout groups, etc.
- The "All Clear" signal must be identified and should be considerably
different than the "Warning" signal. *The Action Plan must be periodically
reviewed by all personnel and drills conducted.
- Consider placing lightning safety tips and/or the action plan in
game programs, flyers, score cards, etc., and placing lightning safety
placards around the area. Lightning warning signs are effective means
of communicating the lightning threat to the general public and raise
awareness.
- First aid recommendations for lightning victims
Most lightning victims can actually survive their encounter with lightning,
especially with timely medical treatment. Individuals struck by lightning
do not carry a charge and it is safe to touch them to render medical treatment.
Follow these steps to try to save the life of a lightning victim:
- First:
Call 911 to provide directions and information about the likely number
of victims.
- Response:
The first tenet of emergency care is "make no more casualties". If the
area where the victim is located is a high risk area (mountain top, isolated
tree, open field, etc.) with a continuing thunderstorm, the rescuers
may be placing themselves in significant danger.
- Evacuation:
It is relatively unusual for victims who survive a lightning strike to
have major fractures that would cause paralysis or major bleeding complications
unless they have suffered a fall or been thrown a distance. As a result,
in an active thunderstorm, the rescuer needs to choose whether evacuation
from very high risk areas to an area of lesser risk is warranted and
should not be afraid to move the victim rapidly if necessary. Rescuers
are cautioned to minimize their exposure to lightning as much as possible.
- Resuscitation:
If the victim is not breathing, start mouth to mouth resuscitation. If
it is decided to move the victim, give a few quick breaths prior to
moving them. Determine if the victim has a pulse by checking the pulse
at the carotid artery (side of the neck) or femoral artery (groin)
for at least 20-30 seconds. If no pulse is detected, start cardiac
compressions as well. In situations that are cold and wet, putting
a protective layer between the victim and the ground may decrease the
hypothermia that the victim suffers which can further complicate the
resuscitation. In wilderness areas and those far from medical care,
prolonged basic CPR is of little use: the victim is unlikely to recover
if they do not respond within the first few minutes. If the pulse returns,
the rescuer should continue ventilation with rescue breathing if needed
for as long as practical in a wilderness situation. However, if a pulse
does not return after twenty to thirty minutes of good effort, the
rescuer should not feel guilty about stopping resuscitation.
- Conclusions
Avoid unnecessary exposure to the lightning threat during thunderstorm activity.
Follow these safety recommendations to reduce the overall number of lightning
casualties. An individual ultimately must take responsibility for his or
her own safety and should take appropriate action when threatened by lightning.
School teachers, camp counselors, coaches, lifeguards, and other adults must
take responsibility for the safety of children in their care. A weather radio
and the use of lightning detection data in conjunction with an action plan
are prudent components of a lightning warning policy, especially when larger
groups and/or longer evacuation times are involved.
3. Discussion and summary
A major result of this meeting was a general agreement concerning the "30-30
rule". The first 30 refers to the number of seconds between "flash" and
"bang" that
initiates safety precautions. The second 30 refers to the number of minutes
after the last flash or thunder in order to establish an "all clear" signal.
Research showing that the average distance between successive flashes is roughly
two to three miles (Krider et al. 1988) was used in prior safety recommendations
(Vavrek et al. 1993; Holle et al. 1995). But López and Holle (1999) found
this distance to be greater in larger and more organized storms. It was also
noted that beyond about 30 seconds (10 kilometers or 6 miles), lightning is
not perceived to be very close even though there is a risk that the next flash
may be at the observer's location. In addition, the lower the storm's flash
rate, the farther apart successive flashes tend to be. These results make it
difficult to formulate a practical recommendation on the safe distance for
every flash.
Some topics were not fully resolved by the attendees. For example, it often
is not easy to identify a safe location. Shelters from rain, sun, and wind
at golf courses, parks, forests, campgrounds, lakes, rivers, ocean shores,
and similar locations are often not safe from lightning, and should be identified
as such with signs. Another uncertainty is how lightning currents propagate
through water and over the ground. Further advances in both basic and applied
science are needed to address these questions.
Multidisciplinary efforts are needed in order to understand how to avoid the
lightning hazard better and how to treat lightning victims. We hope that the
above discussions will eventually lead to a reduction in the number of people
who are lightning victims each year.
Acknowledgments:
We appreciate the very constructive participation of the individuals involved
in the LSG meeting, those with whom we collaborate frequently, and others
who are interested in the problem. It has been difficult to separate the
categories of participants and collaborators, but the responsibility for
unintentional oversights or omissions is entirely ours. We thank Mr. Lee
Lawry of Global Atmospherics, Inc. for reviewing the manuscript prior to
submission, as well as Dr. E. Philip Krider of the University of Arizona
and two anonymous reviewers of the manuscript for their comments.
AMS Copyright Notice
© Copyright 1999
American Meteorological Society (AMS). Permission to use figures, tables, and
brief excerpts from this work in scientific and educational works is hereby
granted provided that the source is acknowledged. Any use of material in this
work that is determined to be "fair
use" under Section 107 or that satisfies the conditions specified in Section
108 of the U.S. Copyright Law (17 USC, as revised by P.L. 94-553) does not
require permission from AMS. Republication, systematic reproduction, posting
in electronic form on servers, or other uses of this material, except as exempted
by the above statements, requires written permission or license from AMS. Additional
details are provided in the AMS Copyright Policies, available from AMS at 617-227-2426
Ext: 250 or amspubs@ametsoc.org.