LIGHTNING SAFETY HANDBOOK

FOR AIRSIDE WORKERS

Published by Civil Aviation Authority of Singapore

April 2007

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Foreword The CAAS Apron Control / Management Service, together with CAAS Development & Engineering and Airport Emergency Service Divisions, have jointly produced this Lightning Safety Handbook for Airside Workers based on the recommendations given by the Lightning Consultants engaged by CAAS to improve the lightning protection at aircraft parking aprons for the safety of the airside workers. The purpose of this Safety Handbook is to provide safety tips to the airside workers on how to avoid being exposed to the risk of lightning strikes while working at the aircraft parking stand at the airport. This handbook provides recommendations on safe practices and aims to educate and raise awareness amongst airside workers on the safe and unsafe areas when working under lightning warning conditions in the airport so that he/she could seek proper shelter and reduce the risk of being injured by lightning strikes. This document by no means covers all the aspects of safety measures that one should adopt and it should be read in conjunction with any other relevant documents available if it is intended for other purposes than for individual and personal safety. Any recommendations towards the improvement of this handbook should be forwarded to:- Chief

Airport Emergency Service Division Civil Aviation Authority of Singapore P O Box 1 Singapore Changi Airport Singapore 918141

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PERSONAL LIGHTNING SAFETY ON CHANGI

AIRPORT APRON BAYS DURING THUNDERSTORMS

CONTENTS:

1.0 Introduction 2.0 Lightning and its threats and interaction with human beings

2.1 Lightning in Singapore 2.2 Threats posed by lightning to persons in airport apron bays 2.3 Interaction of lightning with persons

3.0 Measures taken to overcome/reduce lightning risks and dangers 4.0 Guidance for personal safety at apron bays during thunderstorm 5.0 Application of first aid to lightning victims 6.0 Notes on effect of lightning on persons and treatment for injury – from

CP33:1996 [Ref. 1] 7.0 References 8.0 Figures

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PERSONAL LIGHTNING SAFETY ON CHANGI AIRPORT APRON BAYS DURING

THUNDERSTORMS

1.0 INTRODUCTION Continuation of apron services and operations under all weather conditions is desirable for the efficient operation of Changi Airport. However, attention is drawn to situations when there are lightning threats and hence risks for workers to be out on the apron bays during thunderstorm conditions. The Civil Aviation Authority of Singapore (CAAS) has, through the advice of lightning safety protection experts, taken measures to overcome some of these threats and to reduce the risk of others to low values. These include the provision of lightning stroke interception systems, establishment of procedures requiring the proper earthing of parked aircraft and other prominent structures on the apron bays, ground potential equalization of pavements of apron bays and provision of lightning shelters. It is not possible to provide systems to ensure absolute safety. The risks can only be reduced to reasonable/acceptable values, as in other risks associated with normal living. This document presents the threats and measures taken to overcome/reduce these lightning dangers and risks. The exposure risk for a person in apron bay service operations is estimated. Guidance for personal safety at work in apron bays during thunderstorms and behavioural precautions are given. 2.0 LIGHTNING AND ITS THREATS AND INTERACTION WITH HUMAN

BEINGS 2.1 Lightning in Singapore Lightning activity in Singapore ranks as one of the highest in the world with an isoceraunic level of about 190 thunder days in a year. The lightning ground flash density is estimated at about 12 to 20 strokes per square kilometer per year with its median value at 12.6 [Ref. 1]. Furthermore, there is a variation of roughly 2:1 over a period of about 11 years which corresponds to the sunspot cycle [Ref. 2]. The actual distribution of ground strokes is also dependent on the local terrain and geographical features; in general, with the coastal and hill top regions having a larger share of lightning activity.

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The magnitude of lightning strokes to ground varies from about 5kA to 200kA with a median value of about 30kA. The probability of occurrence of peak lightning current (I) given in CP33:1996, Singapore Standard Code of Practice for Lightning Protection [Ref. 1] is summarized as follows:

p (>I) = percentage of peak current I having values greater than I p (>5kA) = 99%, p (>12kA) = 90%, p (>20kA) = 75% p (>30kA) = 50%, p (>50kA) = 25%. p (>80kA) = 10% p (>130kA) = 1%

2.2 Threats posed by lightning to persons in airport apron bays Persons in the open as in airport apron bays are subject to the following threats posed by lightning.

• Direct lightning strike to person • Touch voltage • Side flash • Step voltage • Transferred voltage through contact with a remotely connected object

2.3 Interaction of lightning with persons

(a) Direct stroke attachment and lightning strike to person – when the tip of the

downward stepped leader has reached a height of some tens of metres above the ground level, the resulting field strength attains a critical value so that a short upward streamer can be initiated from the victim. This small leader current flows for about 50µs. On termination of the lightning leader to the person, a large current due to return stroke attachment occurs. This large amount enters the body followed by flashover over the surface of the body. A combination of internal body current (iB) and surface flashover current (is) then flows through and over the victim [Fig. 1]. A direct strike to a person will most likely result in fatality.

(b) Touch voltage – When an object is struck by lightning, a voltage exists between

two points on its surface. A person in contact with these points may conduct lightning current. When a person is contacting two points, e.g. a strickened parked aircraft and earth, the resulting contact voltage v at the touching point is determined by a resistive and inductive component [Fig. 2].

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v = iR + L di/dt where: v = resulting contact or touch voltage i = main current through the structure R = resistance between the touching points L = inductance between the touching point di/dt = rate of change of main current i (c) Side flash – when a person is near, but not touching, a strickened structure which

conducts lightning current, the potential builds up on the object in the same way as for touch voltage. The resulting potential difference may exceed the electrical breakdown strength of the gap between the object and a person standing nearby. Then a side flash occurs [Fig. 2]. (Note: the electrical breakdown strength of air at atmospheric pressure is about 500kV/m).

(d) Step voltage – Ground potential differences (GPDs) developed, following the

entry of lightning current into the ground, will cause current to flow from one leg, up through the body and down the other leg to ground. Where it flows through the heart, the risk of electrocution is higher as in quadrupeds or 4-legged animals. In 2-legged living beings as in humans, the pathway of step voltages usually does not include the heart; they are often temporarily paralysed from the waist down [Fig. 3].

(e) Transferred voltage – A person who is in contact with a remotely connected

object which is subject to a potential rise due to lightning will be subject to a transfer voltage difference across the point of contact and other parts of the body. An example of this is the use of corded communication devices by a ground staff with the connecting cable plugged into a parked aircraft, or even simply being in contact with the ground.

3.0 MEASURES TAKEN TO OVERCOME/REDUCE LIGHTNING RISKS

AND DANGERS 3.1 Actions by CAAS The Civil Aviation Authority of Singapore (CAAS) has taken measures to overcome/reduce the above mentioned lightning risks and dangers. These are listed as follows:

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(a) Protection against direct lightning strikes to persons

• Use of 22m tall lighting masts, terminal buildings, aerobridges and parked aircraft as lightning stroke interceptors, thereby offering shielding protection to persons in its vicinity or beneath it. The tall lighting masts, terminal buildings and aerobridges are earthed permanently, where possible, to effect protection against lightning. CAAS has also provided earth receptacles [Fig. 4] at all bays for bonding of the aircraft body to earth. For parked aircraft and equipment to provide similar shielding, ground handlers are required to make use of the earth receptacles located on the apron to earth connection points provided for transit earthing of parked aircraft and ground maintenance structures.

• Provision of lightning protected structures at remote bay areas. [Fig. 5]

• The earthing of the above structures will also reduce the voltage rise at these

objects when strickened by lightning, thereby reducing the magnitudes of touch and side flash voltages.

(b) Reduction of step voltages

• Types D6 and A193 pavements of apron bays are already provided with earthed close mesh interconnected BRC slabs. These offer effective ground potential equalization. With the mesh size less than the diameter of a foot print, step voltage is virtually eliminated.

• All existing earth points within the apron bays have been linked together.

Grid systems between apron bays are electrically interlinked.

3.2 Measures to be taken by ground handling agents Similarly, ground handlers working on the apron areas prone to lightning strikes are required to play their part by adopting the following safety measures:

• Provision of vehicles with fully enclosed persons compartments for overhead protection against direct lightning strikes.

• Provision of wireless headsets without trailing cables to prevent transfer

voltage pick up and induction.

• Bonding of the parked aircraft at 3 points

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• Where required, use of electrically conducting clothing of hood, coat, gloves and conductor to the heel of the boot for personal protection. This provides total shielding to the body against voltage difference situations such as touch and step voltages. [Note that this is not suitable nor is intended for direct lightning strike protection]. With the provision of the other systems above, the risks of step and touch voltages are very low and personal protection may not be essential.

4.0 GUIDANCE FOR PERSONAL SAFETY AT APRON BAYS DURING

THUNDERSTORMS For personal safety at the apron bays during thunderstorm conditions, the main hazards to overcome are direct lightning strikes to persons, step potential differences, side flashing and touch potentials from strickened objects. CAAS has taken measures to overcome these threats in designated areas and to reduce the severity and dangers in those areas where total elimination is not possible or is impractical to achieve. It is noted that the exposure risk of step potential is statistically small on the apron and that of touch potential even smaller. As such, work on apron operation/services can continue under areas protected against direct lightning strikes. 4.1 Areas on apron bays protected against direct lightning strikes Protection against direct lightning strikes in the apron bay areas relies on the 22m lighting mast and terminal building as the main lightning intercepting terminals. The parked aircraft, when appropriately earthed to the apron earthing system, also serve to intercept direct lightning strokes. In remote parking bays direct lightning stroke interception is offered by the 22m lighting mast and parked aircraft when appropriately earthed to the apron earthing system. Lightning protected shelters are also provided. In both the above cases and locations, complete coverage against direct lightning strikes over the 78m x 78m apron bay is not possible. The areas which are deemed covered or protected against direct lightning strikes are determined using the concept method of the rolling sphere [Refs. 1, 2, 4 to 6]. In CP33:1996 [Ref. 1] a sphere radius of 45m offers a standard level of protection. This corresponds to the lightning striking distance of a 10kA stroke (with 7% of I < 10kA) which offers a protection level of 93%. Based on this, the areas on the apron bays which are covered or protected by the lightning intercepting structures are shown in the drawings in Figs. 10 to 12. It is clear that the extent of coverage depends on the size and position of the parked aircraft and that in most cases complete coverage of the apron bay against direct lightning strikes is not achievable.

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4.1.1 Lightning safe and unsafe areas No place is absolutely safe from the lightning threat; however, some places are safer than others, e.g.

• Inside terminal building • Inside fully enclosed metallic vehicle (car, bus, truck, aircraft) • Inside lightning safety shelter • In areas under the protective coverage of the lightning intercepting structures

[Figs. 10 to 12] e.g. * Near terminal building – up to about 18.5m * Beneath the passenger loading bridge * Around the 22m lighting mast – up to about 22.5m * Around the parked aircraft. In the case of a B747 or other aircraft of similar size – up to 8.5m along the body side, and up to 21m from the tail Areas outside the above areas and in the open are unsafe and should be avoided during thunderstorms. 4.1.2 Caution and safe work practices Despite being within the lightning safe areas, it is still important to exercise caution and safe work practices. During thunderstorms, essential work should be done briskly and with conscious realization of objects/structures that can be subjected to voltage rises when struck by lightning. One should not unnecessarily be in contact with such structures. These include the body and wings of the aircraft, the footing of the aerobridge or passenger loading bridge, the footing of the 22m lighting mast and other grounded metallic structures. On completion of the tasks at hand, persons should take shelter at nearby buildings or at lightning shelters provided. 4.2 Other dos and don’ts for personal safety Personal safety can be enhanced with good personal conduct and the following of some common sense rules of dos and don’ts. DOs (a) Identify safe and unsafe areas in your workplace beforehand.

(b) Pay attention to lightning alert if available. (c) When one is exposed to nearby lightning:

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• Keep away from unsafe areas • Take shelter in a vehicle, aircraft, building or lightning shelter, if not

performing essential work. • If on open ground remote from shelter, move to a low area such as a drain

and crouch down, singly, with feet together. Footwear or a layer of any non-absorbing material, such as a plastics sheet, offers some protection against ground currents, should there be a nearby lightning flash. If in a group, spread out.

(d) Use wireless headsets only instead of corded one which have trailing wires. (e) Make sure that parked aircraft are earthed to the apron bonding points. (f) Make sure that other prominent servicing, maintenance and other apron

equipment which are likely to be struck by lightning area also earthed to the apron bonding points.

DON’Ts (a) If you are on a vehicle or on board a metallic structure:

• Do not get off but remain in the metallic enclosed structure. • Do not touch or spread over two different structures but stay in only one

structure

(b) Don’t stay in the open, if not performing essential work. (c) Avoid touching metal structures such as metal fences, rails, pipes, lampposts,

etc. (d) Do not seek shelter under a tall tree. (e) Do not load or unload explosive or inflammable material. 5.0 APPLICATION OF FIRST AID TO LIGHTNING VICTIM Most lightning victims can actually survive their encounter with lightning provided that timely first aid and medical treatment is applied. The first 4 minutes are crucial. Persons affected by lightning do not carry a charge and it is safe to touch them to render medical treatment. The following action steps are given:

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1. Call for a doctor and ambulance immediately. The use of a mobile phone, walkie-talkie or any cordless handset is absolutely safe. Avoid the use of a corded handset.

2. If the victim is located in a high-risk area, e.g. open field or unprotected/unsafe

apron bay area, the rescuer must exercise caution. The rescuer must not put himself into danger.

3. In an active thunderstorm, the rescuer needs to choose whether evacuation from

high-risk areas to an area of lesser risk is warranted and should not be afraid to move the victim quickly, if necessary. Rescuers are cautioned to minimize their exposure to lightning as much as possible.

4. If the victim is not breathing, apply cardiac pulmonary resuscitation (CPR)

immediately to restore breathing. 6.0 NOTES ON EFFECT OF LIGHTNING ON PERSONS AND

TREATMENT FOR INJURY – FROM CP33:1996 [REF. 1] The severity of the injuries inflicted on a person by lightning depends on the fraction of the total lightning current that flows through the person’s body and the path of the current through or over the body. The worst situation is where the person is struck on the upper part of the body, so all the current must flow through the trunk, where the heart and lungs are the vitally significant organs, or over the skin. A less dangerous situation is where the person is subjected to step or touch potentials, and only a small fraction of the total current passes through the body, although the pathway taken by the fraction is still important. The effects of lightning include burns to the skin, which are usually superficial, damage to various bodily organs and systems, unconsciousness, but, most dangerously, cessation of breathing and cessation of heart beat. Independently of these electrically related effects, temporary or permanent hearing impairment may be experienced as a consequence of the extremely high sound pressure levels associated with a nearby lightning strike. In the first-aid treatment of a patient injured by lightning, it is essential that breathing be restored by artificial respiration and blood circulation be restored by external cardiac massage, if appropriate. These procedures should be continued until breathing and heart beat are restored, or it can be medically confirmed that the patient is dead. It should also be noted that the usual neurological criteria for death may be unreliable in this situation. There is no danger in touching a person who has been struck by lightning.

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Lightning strike victims are sometimes thrown violently against an object, or are hit by flying fragments of a shattered tree, so first-aid treatment may have to include treatment for traumatic injury. Subsequent treatment of a lightning strike patient is a specialized area with important differences from the treatment of injuries inflicted by electric power current. For example, the nature of the burns, and the extent of damage to underlying muscle tissue tends to be severe with electric power current, but mild with lightning current. Neurological and cardiac injuries also are different, and follow different courses.

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REFERENCES : 1. CP33 : 1996, “Singapore standard code of practice for lightning protection”,

Singapore Institute of Standards and Industrial Research, 1996. 2. BS 6651:1999, “Protection of structures against lightning”, British Standards

Institution, 1999. 3. A.C. Liew, “Report on review of lightning protection at Changi Airport apron

bays and safety of airside workers and recommendations for improvements”, submitted to Civil Aviation Authority of Singapore”, 27 September 2004.

4. AS 1768:1999, “Lightning protection”, Standards Association of Australia,

1999. 5. IEC 1024, “Protection of structures against lightning”, International Electro

technical Commission, 2004. 6. NFPA 780, “Lightning protection code”, National Fire Protection Association,

1992, USA. 7. Review and improvement of apron lightning protection by Isolectra Far East,

2000

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Fig. 9 Direct lightning strike to person

Fig. 2 Touch voltage and side flash to person

Fig. 1 Direct lightning strike to person

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Fig. 3 Step voltage

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Figure 4 Earth receptacle with cover closed and opened

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Fig. 5 Lightning Shelter There are 9 lightning shelters constructed at the remote aircraft parking stands (PS) and 2 at the engine run up stand (ERUS) of Singapore Changi Airport. They are located at the following locations: 1. PS103 2. PS 201 3. PS 206 4. PS 208 5. PS 300 6. PS 304 7. PS 308 8. PS402 9. PS 404 10. ERUS 606 11. ERUS 609

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Figure 6 Layout of Singapore Changi Airport

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Figure 7 Tape with clamps for bonding aircraft to earth receptacle

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Figure 8 Illustration of protective clothing of hood, coat, gloves and boots with external layer of electrically conducting material for reduction of touch and step potential hazards

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• Shaded areas = protected against direct lightning strikes (AREAS UNDER AND AROUND THE AIRCRAFT ARE SAFE ONLY IF THE AIRCRAFT IS BONDED TO EARTH)

⊕⊕⊕⊕ 22m lighting mast

Fig. 9 Plan view of areas (shaded) covered or protected against direct lightning strikes by the terminal building, 22m lighting mast and parked aircraft – as determined by the 45m rolling sphere method

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• Shaded areas = protected against direct lightning strikes (AREAS UNDER AND AROUND THE AIRCRAFT ARE SAFE ONLY IF THE AIRCRAFT IS BONDED TO EARTH)

Fig. 10 Elevation view of areas covered or protected against direct lightning strikes by the terminal building, 22m lighting mast and parked aircraft – as determined by the 45m rolling sphere method

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PROTECTED BY REAR WING PROTECTED BY TAIL PROTECTED BY FUSELAGE

• Shaded areas = protected against direct lightning strikes (AREAS UNDER AND AROUND THE AIRCRAFT ARE SAFE ONLY IF THE AIRCRAFT IS BONDED TO EARTH)

Fig. 11 Front and back section elevation views of areas (shaded) covered by a parked aircraft in an open bay