25 Cardiopulmonary Resuscitation and Early Management of the Lightning Strike Victim

Chapter 25 / CPR and Lightning 425 25 Cardiopulmonary Resuscitation and Early Management of the Lightning Strike Victim

Mary Ann Cooper, MD and Sara Ashley Johnson, MD

CONTENTS INTRODUCTION MECHANISM OF LIGHTNING STRIKES MECHANISMS OF LIGHTNING INJURY MANAGEMENT OF LIGHTNING VICTIMS CONCLUSIONS AND PREVENTION REFERENCES

INTRODUCTION In the past 40 years, lightning has killed more people than any other storm-related phenomena except floods (1). On average, lightning causes 75 to 100 deaths per year (1). The number of nonfatal injuries is estimated to be 10 times the number of deaths, but the exact number is not precisely known because of incomplete reporting (2). A risk table for lightning injury is available at www.lightningsafety.noaa.gov and is excerpted as Table 1. Contrary to popular belief, death caused by lightning is not as a result of burns. Severe burns are uncommon because the majority of lightning energy flashes around the outside of the individual and is simply not around long enough to burn through the skin in most cases, although secondary steam, hot metal, and other incidental superficial burns may be observed (3,4). Lightning is a nervous system injury. Of the 90% who survive lightning strike injury, a significant number have disability from brain injury, neurocognitive deficits, or chronic pain syndromes (4–6). A lightning strike victim is highly unlikely (p < 0.0001) to die unless he or she has suffered cardiopulmonary arrest (CPA) imme- diately at the time of the strike (5). Although complications of postarrest anoxia or depression and suicide may lead to death after the acute event, the only immediate cause of death is cardiac arrest (CA) at the time of the strike (5). Although autonomic injury is known to occur and many patients report arrhythmias and chest pain, the etiology and occurrence of long-term cardiac sequelae is unclear and poorly documented (4).

From: Contemporary Cardiology: Cardiopulmonary Resuscitation Edited by: J. P. Ornato and M. A. Peberdy © Humana Press Inc., Totowa, NJ 425 426 Cardiopulmonary Resuscitation

Table 1 Odds of Becoming a Lightning Victim US 2000 Census population 280,000,000 Reported deaths 85, injuries 315 1/700,000 Actual deaths 120, injuries 1050 1/230,000 Life expectancy of 80 years 1/3000 Ten people affected for every one hit 1/300

Unlike triage in common multicasualty situations, with lightning, anyone who shows signs of life such as moaning or groaning will survive, albeit perhaps with sequelae, and may be attended to later (4). Because the only cause of immediate death is CPA, the goal of treating lightning strike victims is to resuscitate and stabilize those in arrest. Besides prevention, probably the best way to minimize acute lightning-related death is to opti- mize cardiopulmonary resuscitation (CPR) and postresuscitation care. This chapter pro- vides the background information necessary to understand the pathophysiology of lightning strikes and the injury patterns they produce, describe the initial management of all lightning strike victims, and detail the specific management of victims based on clinical presentation and electrocardiogram (EKG) findings.

MECHANISM OF LIGHTNING STRIKES Although lightning may occur in many forms, the most common discharge is the negative cloud to ground (CG) stroke. Lightning occurs when sufficient charge differen- tial is built up in a cloud to cause electrical discharges. Discharges begin as horizontal intercloud lightning that jumps in spurts 30 to 50 meters long. It branches, then retreats to the source only to refill the main established streamer channel and branch again at the endpoint of each of the 30- to 50-meter lengths, repeating this cycle over and over again in a matter of milliseconds. This alternating retreat and branching is what causes the sawtooth appearance of lightning. Some spurts never progress past their first or second generation and in most storms the majority of the streamers remain in the cloud unseen or perhaps causing only a brightening of the cloud. In the average storm, about 10% will approach the ground at some stage as downward leaders. Downward leaders continue branching in 30- to 50- meter segments until they get close to the ground. This branching and retreating mechanism in part explains why lightning does not “always hit the tallest object.” The downward leader only “sees” a 30- to 50-meter radius from the tip of its last division so that when lightning does not hit the obvious “tallest” structure in an area it is usually because that structure is outside this 30- to 50-meter radius. Thus, the goal posts on a football field are unlikely to protect someone standing in the middle of the field (4). As the storm cloud moves across the land, an opposite, usually positive charge is induced in the ground. Surges of charge move through any upward projecting object, whether it is a tree, a TV tower, a person, or a blade of grass and produce upward streamers. Occasionally, these may be seen as St Elmo’s Fire. More often, the upward streamers are invisible and not appreciated except perhaps as static electricity causing one’s hair to stand on end (4). Chapter 25 / CPR and Lightning 427

Fig. 1. Lightning casualties by state 1959–2003. (Thanks to Ron L. Holle for use of Fig. 1.)

One or more of these upward streamers may connect with a downward streamer to complete the cloud to ground channel in a process called attachment. There are often multiple upward streamers that do not form a connection but are of a magnitude sufficient to cause injury (7,8). After attachment occurs, several spaced strong surges of energy rush upward as return strokes and down again as dart leaders, causing the flickering and brightening that we see in the main lightning pathway. In the United States, there are approx 20 million CG flashes detected each year, most frequently in the summer months (9). More than half of lightning strikes have two ground contact sites or more. CG lightning is most common in the southeastern United States, but deaths and injuries are most common along the Gulf and Atlantic coasts, the major US river valleys and over the Rocky Mountains (Fig. 1). Injuries peak in July and in the mid-afternoon hours on Saturdays and Sundays. One-third of lightning injuries are work- related (1,4). 428 Cardiopulmonary Resuscitation

MECHANISMS OF LIGHTNING INJURY In attempting to define the injury mechanism for a particular person, the question arises: “Does the lightning energy go down through or around the person from the cloud to the ground, up from the ground to the cloud or by some other mechanism?” At least five mechanisms of lightning strike injury have been identified: direct hit, side splash to a person from another object, contact when the person is holding onto an object such as a fence that is struck, ground current/ground arcing and uncompleted upward streamer, hypothesized by engineers for years but only recently documented in the medical literature (4,10). Further complicating the issue is the fact that the majority of the energy probably flashes around (“flashover”) rather than through the person (4). Although it is reasonable to infer that a direct strike is more likely to cause death, there is no hard evidence that this is the case. Although theoretically knowledge of the mechanism of injury should be helpful in anticipating the level of care required, pragmatically it is nearly impossible to tell which mechanism has injured a particular victim. When there are witnesses, they are often too upset or injured themselves to give a good account. Lightning strike is so instantaneous that even the most focused and expectant observer has difficulty telling where the energy traveled. Further complicating the history is that victims often have few or no burns. Even in those that do, the burns cannot be used to tell where the energy has traveled as the burns are often secondary to sweat or rainwater that has heated up and caused steam burns, from hot metal burns from necklaces, belts, pocket coins, or other secondary burns. The terms “entry” and “exit” have no meaning with lightning injuries (3). The first organized study of lightning injuries in 1980 gives some clues of prognosis (5). Those with burns about the head are more likely to have CA and die as are those with burns to both legs. However, burns from one arm to a leg or between arms were not associated with a higher incidence of death or CA. Many survivors have amnesia for the event (5). However, they will almost always and quite innocently reconstruct a composite mechanism of injury consistent with what they have heard from the paramedics who transported them, from their physicians, their rela- tives, from what they read and from any burns that they may have received. This recon- struction may or may not have any relationship to what actually happened (4). However, the story is usually harmless and attempting to dissuade the survivor or their family from their believed mechanism is a waste of time, does not improve outcome and generally leads to dissatisfaction on all sides. The lightning literature is clouded with assumptions to the mechanisms of injury and their outcomes. Unfortunately, most of the lightning cardiac literature consists of case reports with almost no organized studies relating mechanism of injury, EKG findings, outcome, or other cardiac questions. Direct Hit Perhaps the most dramatic strike is a “direct hit.” Classically, this occurs in unsheltered, open areas such as sporting or farm fields, golf courses, or mountains. Although specific data has not been reported, direct hits are assumed to be the mechanism most likely to cause CA or severe cardiac damage because the force of the strike is transmitted directly to the individual and not decreased by the interposition of trees or other objects. In a 1993 study of cardiovascular effects of lightning strikes, Robert Lichtenberg described four patients reportedly with direct strikes by lightning, three of whom had myocardial injury. One victim suffered CPA in the field, arrived in the emergency depart- ment (ED) in asystole. Despite aggressive resuscitation and a return to sinus tachycardia, Chapter 25 / CPR and Lightning 429 this patient was pronounced dead 36 hours later. The remaining two victims had ST segment elevation on their EKGs, elevated cardiac enzymes, and echocardiographic evidence of global ventricular dysfunction (11). In 1981, B.L. Chia described a 23-year- old woman reportedly directly hit by lightning, who arrived in the hospital in pulmonary edema, which was successfully treated with diuretics and digoxin (12).

CONTACT AND SIDE-SPLASH INJURIES Contact and side-splash injuries are probably much more common than direct hits. In “contact” injuries, lightning strikes an object such as a tree or fence and a portion of the strike’s energy travels to anyone touching the object. A side-splash injury occurs when lightning strikes an object but some of the energy splashes through the air to a nearby person. People who gather under trees during thunderstorms are often injured in this way and sometimes lightning may be witnessed to travel sequentially from one victim to another. Numerous reports of cardiac sequelae following contact and side-splash injuries exist (11,13–16), ranging in severity from Lichtenberg’s three patients, all of whom had nonspecific ST-T wave changes but no echocardiographic abnormality (11), to J. P. Kleiner’s report of a man whose tent was struck by lightning who developed ventricular failure requiring diuretics and a 3-week hospital stay (13). Although the vast majority of side- splash injuries occur outdoors, a not insignificant number occur inside buildings, often via telephone wires or from plumbing or electrical fixtures (4,17).

GROUND CURRENT When lightning strikes the earth, the energy spreads radially, and may pass up through people or animals near the lightning contact point. Sports teams, soldiers on maneu- vers, and other groups of people have been injured in this way with mortality ranging from 0 to 23% (18–23). Kitigawa has recently further divided the ground current effect: one where current flows through the ground with little energy flow to those standing on it and therefore minor injury, and ground arcing where energy arcs above the surface of the ground, through or around the person as part of its pathway, similar to side splash. The second type of injury, although it may occur on flat surfaces, is more likely to be seen on uneven terrain and mountains and is more likely to cause severe injuries because of the greater energy exposure of the person (24). Lichtenberg described 12 patients affected by ground current strikes: although three had nonspecific ST-T wave changes on electrocardiogram, only one had CK-MB release, and none had an abnormal echocardiogram (11).

UPWARD STREAMERS A fifth mechanism for injury by lightning has been hypothesized by lightning and electrical researchers for many years but only recently have cases been specifically studied for this mechanism (7,8,10,23,25). Upward streamers are surges of charge that begin at the ground, rush up through or around the person but do not connect with the downward leader from a cloud to complete the lightning channel (10). Upward streamers may occur a kilometer or more from the charged cloud. Cooper described a case in which an upward streamer passed through a member of an electrical crew. Paramedics arrived to find the patient in ventricular fibrillation (VF). Despite defibrillation and intubation, the patient never regained a perfusing rhythm and was pronounced at the ED (10). Because this mechanism is newly documented, no cases of hospital management for surviving patients are available for review. 430 Cardiopulmonary Resuscitation

MANAGEMENT OF LIGHTNING VICTIMS Diagnosis When witnesses are available or when the individual is alert enough to provide his or her own history, making the diagnosis of lightning strike is not difficult. However, when found confused and alone outdoors, a lightning strike victim may be initially thought to have had an intracranial hemorrhage, a seizure, or suffered an assault (4). Because lightning can injure victims indoors, the diagnosis should be considered in anyone found confused and unconscious during or shortly after a thunderstorm, particularly when no other mechanism of illness is evident (4,17). Physical clues that a patient has been struck by lightning include clothing partially or completely exploded off, linear or punctate burns, missing shoes, ruptured tympanic membranes, and the rare but pathognomonic keraunographic markings or Lichtenberg figure (it is not known if this is any relation to R. Lichtenberg [4]). These are an evanes- cent feather or fern-like pattern that usually disappears within a few hours and are not true burns. Historically, they were attributed to the imprint of plants the individual had been near when struck but more recently thought to represent a fractile pattern from electrons tracking over the skin during lightning strike (4,26).

CAUSES OF CARDIAC ARREST FROM LIGHTNING It has been hypothesized that a primary arrest occurs from the strike energy itself similar to the short asystole that occurs after defibrillation but that a healthy heart resumes cardiac activity after the lightning insult. The respiratory arrest lasts much longer causing a secondary CA that may be irrecoverable (4,5). It was further hypothesized that early and adequate ventilatory support could make a difference in the outcome of the individual. Simulated lightning strike to animals in the laboratory has confirmed this sequence of primary arrest and pause, often with recovery, but prolonged respiratory arrest and secondary CA with higher shock doses (26,27). Even the animals that survived had arrythmias for a short period of time. However, in the fatally injured, ventricular tachycardia (VT), bradycardia, intermittent and variable blocks, sometimes fibrillation, and eventually (secondary) asystolic CA developed (26,27). Recent unreported animal studies have also confirmed a significant effect on heart rate variability from autonomic nervous system injury at the time of the strike (27). Some early references recommended very prolonged resuscitation for lightning victims based on a mechanism of “suspended animation” for lightning survivors in which the brain and other organs are protected by some unknown mechanism so that resuscitation might be successful and without deficits if it were carried for a much longer time than would be considered useful by most clinicians. A more recent case series of survivors with QT prolongation after the strike hypothesized that this may contribute to a torsade mechanism that has been confused with “suspended animation” perhaps with some perfusion, no palpable pulses but yet some recovery (28). There is no reason to believe that CA from lightning is more brain “protective” than other forms of CA to young healthy individuals. Studies have not been done to determine the relative contributions of autonomic nervous system injury, direct damage to conducting and pacing pathways or to the heart itself, injury to respiratory and cardiac control centers in the brain, timing of the lightning strike during the cardiac cycles, or other as yet unknown mechanisms to the CA or how these affect recovery or long-term cardiac effects. Chapter 25 / CPR and Lightning 431

INITIAL RESUSCITATION AND STABILIZATION OF LIGHTNING STRIKE VICTIMS In treating the lightning strike victim, the first step is to establish airway, breathing, and circulation, as well as assure the safety of the individual and the rescue crew who are often responding during an active thunderstorm. It may be necessary to move the victim to a safer area before adequate resuscitation attempts can begin Unfortunately, not enough research has been done with lightning victims or animal models to allow tailored recommendations for cardiac resuscitation of lightning victims. Established ACLS protocols should be followed with victims of lightning strike who are unresponsive and without spontaneous respirations in the field: an airway should be established, and CPR performed until a cardiac rhythm can be determined. More directed treatment with cardioversion, defibrillation and/or epinephrine, atropine, and other standard ACLS medications should proceed according to the most recent guidelines. The resuscitation of lightning victims may be complicated by hypothermia from wet clothing or cold conditions on mountains and other high-risk lightning areas. It is also too early to tell if the growing availability of automatic external defibrillators (AEDs) to first responders or in sports venues, schools, and other areas will produce better outcomes for lightning victims, although this author is aware of three separate recent unpublished cases in which the use of an AED resulted in successful resuscitation. An AED trial application can cause no harm provided other resuscitation and rescue protocols continue as well. There is no reason to believe that CA from lightning is more brain “protective” than other forms of cardiac arrest to young healthy individuals. Old anecdotal reports of “suspended animation” and miraculous cures after very prolonged resuscitation have not been substantiated in more recent literature and should be probably included among the large number of other lightning myths that abound (3). However, consistent with histori- cal evidence in the literature, ventilatory assistance may need to be prolonged after a successful cardiac resuscitation.

CESSATION OF RESUSCITATION The decision to abandon resuscitation efforts should be guided by the clinical scenario including how long the person has been without adequate resuscitation and their response after standard ACLS measures have been started. What constitutes a reasonable period will depend on the most recent ACLS guidelines and the judgment and experience of the clinicians involved in the lightning strike victim’s care but certainly if there is no response within thirty minutes, termination of resuscitation should be considered as it is unlikely that the individual will survive with useful brain function after this length of time. When arrest occurs in a wilderness setting far from the benefits of electrical intervention, drugs, and medical care, rescuers should be absolved of any guilt in terminating resuscitation efforts if there is no response within twenty or thirty minutes or when rescuers become exhausted, whichever occurs first (4,29).

EVALUATION AND TREATMENT OF MORE STABLE LIGHTNING STRIKE VICTIMS In lightning strike victims with stable airway and a cardiac rhythm, adequate ventila- tion should be assured and a secondary survey performed. Although this chapter focuses on the cardiopulmonary manifestations of lightning strike, it should be noted that lightning victims may suffer a number blunt injuries including pulmonary contusions, back and brain injuries and occasionally fractures from both the explosive nature of the strike around them or from being thrown by the intense muscle contractions induced by the 432 Cardiopulmonary Resuscitation electrical energy (4,30,31). All trauma victims should be undressed in order to identify other injuries as well as to remove wet clothes that may be contributing to hypothermia. Carotid and femoral pulses are usually palpable in lightning strike victims who are not in CA. If the patient is hypotensive without palpable distal pulses, cardiogenic, hypov- olemic, and spinal shock should be ruled out. However, in many cases of lightning strike, distal pulses may be affected even in the presence of normal blood pressure and cardiovascular stability. A significant number of lightning victims may exhibit keraunoparalysis with cool, mottled, pulseless extremities, which is thought to be the result of sympathetic instability and intense vasospasm (4,31). In Cooper’s study of severely injured lightning strike victims, a full two-thirds had some degree of lower extremity paralysis, in which the affected extremities were cool, mottled, insensate, and pulseless (5). The vast majority of lightning strike victims not in arrest or congestive heart failure on arrival to the hospital will have normal cardiovascular exams and electrocardiograms. These patients are unlikely to deteriorate (4,5,11). Asymptomatic patients with normal electrocardiograms and no other injuries requiring admission do not need cardiac enzymes measured and may be safely discharged from the ED with instructions to follow up with their primary-care physician.

EKG CHANGES Several types of EKG abnormalities in lightning strike victims have been described.

QT PROLONGATION In 1987, A.B.D. Palmer described a case of lightning induced q-t segment prolongation (15). The patient had a modestly prolonged QTc (0.36 seconds) on admission. Thirty-eight hours later, the QTc was an impressive 0.68 seconds, and by day 3, the QTc had shortened to 0.5 seconds. Fortunately, this patient’s rhythm never degenerated into torsades de pointe or VF. In 1993, Andrews reviewed literature involving lightning strike victims and their electrocardiograms, and found that what Palmer had published as an isolated case report was far from uncommon. When a precise QTc could be calculated from available data, 63% were prolonged (28). Additionally, the overall trend mirrored that described by Palmer: QTc intervals became increasingly prolonged in the first few days of recovery and slowly returned to normal. Although the mechanism by which a lightning strike delays ventricular repolarization prolonging the QTc interval is not well understood, the implications are clear. The increased risk of developing torsade de pointes VT must be considered so that monitored admission of lightning strike victims with this abnormality is probably prudent. In many cases, the QTc will normalize over a few days. If this fails to occur, Holter monitoring and electro- physiological studies may be considered (15).

NONSPECIFIC T-WAVE AND ST-T CHANGES T-wave inversion and ST-T changes that do not fit typical coronary ischemia patterns are often observed in lightning strike victims. Most of these patients are asymptomatic and the vast majority of the ECG changes resolve spontaneously over a period of days to weeks (4,11–14). It may be that these usually self-limited changes are as a result of direct myocardial damage caused by the lightning rather than vascular ischemia. Of the six patients Lichtenberg studied with nonspecific ST-T wave changes, all had normal echo cardiograms and uneventful recoveries (11). Chapter 25 / CPR and Lightning 433

ANATOMICAL ST-ELEVATION AND T-WAVE INVERSION There are several documented cases of ST segment elevation after lightning strike (11,15,32). Lichtenberg described a patient, reportedly directly struck, who presented with ST elevation in the anterior and precordial leads and anterior wall motion abnormalities on echocardiogram (11). The patient never developed heart failure and wall motion returned to normal in a few days. Jackson and Palmer described patients with elevated ST segments in the inferior leads who remained asymptomatic, and whose electrocardiogram changes resolved within several days (15,32). T-Wave inversion consistent with vascular ischemic patterns has been reported (12,13) in both anterior and inferior patterns. Electrocardiograms normalized in a few weeks in all of these cases ECG changes such may be caused by injury to the coronary arteries or by spasm resulting from high levels of catecholamines after lightning strike (4,10). When the damage to underlying muscle is extensive enough, congestive heart failure and pulmonary edema can develop (11–13). Kleiner described an 18-year-old who developed severe shortness of breath three hours after being struck (13). The patient’s chest x-ray showed severe pulmonary edema and Swan-Ganz catheterization measured his pulmonary capillary pressure at 25 mmHg. The patient improved with diuretic therapy and did not require inotropic support. Patients with changes on EKG should be evaluated for signs of congestive heart failure. If significant comorbidities such as age or underlying heart disease exist, they may warrant echocardiogram, telemetry admission, or other interventions.

LONG-TERM PROBLEMS There are several common complaints of lightning survivors that may be cardiac in origin: palpitations, chest pain, hypertension, dizziness, and near syncope (4). Many survivors complain of palpitations for a considerable period of time after lightning injury. They may also complain of shortness of breath, dizziness, and other symptoms so that from the history alone it is difficult to tell whether the palpitations are as a result of panic attacks or are true arrhythmias. No malignant arrhythmias have been reported as sequelae of lightning injury but there are also no reports in the literature of investigations of these complaints. Some survivors experience frequent chest pain. Although a cardiac work up is usually indicated, it is often negative so that the etiology for the chest pain in these cases remains unclear. Some may be as a result of musculoskeletal injury from blunt injury caused by the strike (4). Other reasons have not been investigated in relationship to lightning. There have been a number of cases of worsened hypertension or new hypertension documented after a lightning strike. Although lightning is well known to cause autonomic damage, it has not been studied as an independent cause of hypertension. Dizziness and tinnitus, frequent complaints of lightning survivors, is most often from damage to the eighth cranial nerve. Near syncope may be confused with new onset temporal lobe, partial complex seizure or hypothalamic seizures, which may have an onset as late as 2 years after the injury. Unfortunately, routine electroencephalograms measure only surface seizure activity and miss 50–100% of seizures that occur in deeper structures, further burdening many of these patients with the diagnosis of “pseudoseizure.” 434 Cardiopulmonary Resuscitation

Table 2 Lightning Safety Guidelines Know the weather forecast before starting an outdoor activity. Have a Lightning Safety Plan that includes safer places to go as well as the time to get there. Know your local weather patterns and keep an eye on the sky. At the first sight of lightning or sound of thunder, begin implementation of your Lightning Safety Plan. Safer areas include substantial buildings and fully enclosed metal vehicles with the windows rolled up. Avoid tall structures such as towers, mountains, and trees. Avoid open fields, open vehicles, and being near or in water. Avoid contact with metal conductors or using small “shelters.” Do not resume outside activity until 30 minutes after the last lightning and last thunder.

Prevention Although no place can be guaranteed to be totally safe from lightning strike, certain precautions can be taken to minimize the risks of lightning injury. Lightning warnings by the National Weather Service is uncommon, unlike many other disasters for which the government issues warnings hours to days in advance, so the individual must be responsible for making the best choices for their own personal safety as well as others for whom they may be responsible. Lightning Safety Guidelines for individuals, small groups and very large groups such as sports stadia audiences are outlined in Table 2 and are available in greater detail from other sources (29,33–35). These guidelines, adopted by the National College Athletic Association in 1987, the National Athletic Trainers Association in 2000, and the entire Dallas Public School system in 2000 are becoming more widespread in both sporting, occupational and public venues.

CONCLUSIONS AND PREVENTION Although lightning is the second largest storm killer annually in the United States, exceeded only by floods, it is still reasonably uncommon to suffer any lasting cardiac damage as a result. For those patients who arrest from lighting strike, recent advances in the acute care of CAs—improvements in the emegency medical services system, increased availability of AEDs and decreased time to resuscitation, and optimized intensive care for those who survive the initial insult—are likely to increase survival. Additionally, knowledge culled from the dozens of case reports of cardiac effects of lightning strike makes it easier for emergency physicians and cardiologists to predict which patients are likely to recover and which require monitoring. Even as the treatment of lightning strike victims improves, we should not forget that injury from lightning strikes is, more often than not, preventable. Lightning Safety Guide- lines, now published in many venues, can help individuals and organizations to develop lightning safety action plans that can prevent injury Table 3 (29,33–35). Chapter 25 / CPR and Lightning 435

Table 3 Components of a Lightning Action Plan Develop a Lightning Safety Plan Train personnel to be familiar with the plan Access up-to-date weather information If detection or warning systems are used, train personnel in their use. Designate safer areas Plan for routing and evacuating people Display appropriate signage Educate of the event’s participants about the Plan Use a Warning Signal—different from All Clear Signal Carry out regular plan drills Review and modify plan as needed

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