Livro Environmental Hazards

8/3/2019 Livro Environmental Hazards

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A VOLUME IN THE ROUTLEDGE PHYSICALENVIRONMENT SERIES

Edited by Keith RichardsUniDcysity of Cmnbridge

The Routledge Physical Environment Series presents autboritative reviewsof signiticant issues in pbysical geography and the emironmental sciences.Tbe series aims to become a complete text library, covering a range ofthemes in pbysical geography and environmental science, including speciticprocesses and environments, environmental cbange on a variety of scales,policy and management issues, as well as developments in methodology,techniques and pbilosophy.

Other titles in the series:WATER RESOURCES IN THE ARID REALM

E. Anderson and C. AgnewICE AGE EARTH: LATE QUATERNARY GEOLOGY AND

CLIMATEA. Dawson

MOUNTAIN WEATHER AND CLIMATE, 2ND EDITIONR.e. Barry

Forthcoming:TH E GEOMORPHOLOGY OF DESERT DUNES

N. LtmcasterGLACIATED LANDSCAPES

M. SharpHUMID TROPICAL ENVIRONMENTS AND LANDSCAPES

R. WalshSOILS AND ENVIRONMENT

S. E!lis and A. MellorPROCESS, ENVIRONMENT AND LANDFORMS: APPROACHES

TO GEOMORPHOLOGYK. Richards

ENVIRONMENTALHAZARDS

Assessing risk and reducing disaster

Keith Smith

I London and N ew YorkUNIVERSITAT POMPEU FABRA

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1HAZARD IN THEENVIRONMENT

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AWARENESS OF HAZARDSo-called 'natural hazards' have always been a pan oE human history. But,in the modern world, there is an increasing paradox between the outstand

achievements in science and medicine, which make life safer andhealthier, and the continuing death and destruction associated with theextremes of nature. The paradox is complicated by the fact that scienceitself is not without hazard and has led to the comparatively recent emergenee of 'man-made' threats which arise from the misapplication and failureof technology. People are now at risk not only from geophysical events,

as earthquakes and floods, but also from industrial explosions, 1of toxic substances and major transpon accidents. A growing 1,

11awareness of hazard is funher encouraged because al! disasters make news.The graphic results of hazards, both natural and man-made, feature repeat 11I1111on television screens throughout the world and seem to make ever ,1 1more frequent headlines. 11

'11What, then, is the reality? Is the world becoming a more dangerousplace? Why do we scem unable to use the available scientific knowledge 11 11to reduce hazards? Is the frequency and/or magnitude of natural hazard II!!,increasing? What is the added risk from the newer technological hazards? 11

1, 1Is human society becoming somehow more vulnerable to the same inci 'dence of hazard? On the other hand, with the progressive improvement 11 ,1,in global communications, is it simply that disasters are reponed more ,1,efficientiy than before and, to that extent, are largely a media invention? 1

1'More subtly, perhaps the concern for hazards is confined to the wealthy, 11" 1developed nations who have eliminated so many threats, such as bubonic 111111

11 1lems? In any case, how can we define an acceptable level of risk and how .1 ' "plague or tuberculosis, that they now worry about les s immediate prob-

11 'Idoes this vary between different communities across the globe? Is it11 :realistic ro look forward to a world from which environmental hazard has 1been eliminated? 11'1l'1At the present time, we lack definitive answers ro most of these 111 :1,

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THE NATURE OF HAZARD HAZARD IN THE ENVIRONMENTquesrions. This is partIy because scienrific inreresr in environmental hazards is of fairly recenr origino Exrreme natural events have attracred attenrion for hundreds of years. Attemprs to defend individual buildings againsrearthquakes dare back ar leasr 2,000 years. Bur sysrematic, policy-orienredresearch into hazard assessmenr, and hazard reducrion, really began wirhrhe work of Gilbert Whire (1936; 1945), wh o was rhe firsr to recogniserhar engineering schemes were nor rhe only way to rackle flood problemsin rhe USA. He and his colleagues conrinued to research alternarive srraregies for flood hazards unril, in 1967, a collaborarive programme of invesrigarion was mounred ar rhe Universiry of Chicago (larer rransferred to rheUniversiry of Colorado), Clark Universiry and rhe Universiry of T oron roto apply rhe findings to orher geophysical hazards and to settings orherrhan North America. Ar about rhe same time, hazard-relared research wasbecoming esrablished in a wide variery of academic disciplines rangingfrom geology to sociology.

The pace quickened in rhe 1970s for several reasons. FirstIy, exrremenatural evenrs suddenly became more prominent. In large parr rhis wasdue to rhe climaric flucruarions of rhar decade which produced rhe Saheliandroughr, rhe failure of rhe Peruvian anchovy harvesr, rhe 1975-6 droughrin north-wesr 'Europe and rhe severe Norrh American winrers of 1976-7and 1977-8. These evenrs exposed rhe vulnerabiliry of many counrries,including advanced narions, to climaric variabiliry. Ar rhe same rime,neocarasrrophism became fashionable amongsr physical geographers. Thisconcepr was firsr inrroduced by palaeontologisrs concerned wirh rhe rapidexrincrion of life forms and was rhen adopred by rhose geomorphologisrsanxious to acknowledge rhe significance of large, rare evenrs in mouldingrhe landscape. Secondly, many physical geographers saw a need to makerheir work more relevanr to human affairs, and natural hazards became asrrong focus for rhe srudy of rhe relarionships berween narure and sociery.This approach was greatIy facilirared by rhe view of hazards as occurringar rhe inrerface berween rhe natural processes of rhe environmenr andpeople seeking a living rhrough rheir use of rhe earth and irs naruralresources. Thirdly, rhere was a growing belief rhar sorne of rhe apparenrinabiliry to cope wirh hazards lay in differences berween rhe 'real' worldand how ir was viewed in pracrice by managers and decision-makers. Inturn, rhis gave momentum ro rhe research on environmental hazard perceprion already begun by sorne human geographers.

Thus, rhe 1970s saw rhe publicarion of several importanr books,especially by rhe North American research school inspired by Whire(Whire, 1974; Whire and Haas, 1975; Burton et al., 1978). These worksrepresenr a plareau of achievemenr which, in rhe 1980s, was modified byrhree major changes in perspecrive. Firstly, more emphasis was given torhe relarionships berween natural hazards and economic underdevelopmentin rhe Third World, in particular rhe exrenr to which economic dependency

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exacerbares rhe effecrs of geophysical events. Secondly, following imporranr signals of rechnological hazard in rhe 1970s - such as rhe Flixborough(UK) explosion in 1974, rhe release of dioxin ar Seveso (Italy) in 1976 andrhe nuclear incident ar Three Mile Island (USA) in 1979 - so-called 'manmade' hazards began to receive more arrenrion. The year 1984 was a clearrurning poinr wirh several major indusrrial accidents, including rhe releaseof merhyl isocyanare ar Bhopal (India), which alone claimed well over2,000 immediare dearhs. Thirdly, rhe multidisciplinary narure of hazardresearch has widened to rhe poinr where earlier disrincrions berween'narural' and 'man-made' hazards are ever more difficulr to susrain.

In rhe lare rwentierh century, awareness of environmental hazard hasnever been grearer. The idea of a cooperarive international programme toreduce rhe losses from natural hazards was firsr proposed by Dr FrankPress, president of rhe US N arional Academy of Sciences, in 1984 (Housner, 1987). Following several years of prepararion, rhe Unired NarionsGeneral Assembly in December 1989 finally adopred Resolution 44/236proclaiming rhe 1990s as rhe Inrernarional Decade for N arural DisasrerReducrion (IDNDR). The objecrive of rhe Decade, as srared in rhe annexeto Resolurion 44/236, is:

to reduce rhrough concerted internarional acrion, especially indeveloping countries, rhe loss of life, property damage, and social andeconomic disruprion caused by natural disasrers, such as earthquakes,windstorms, rsunamis, floods, landslides, volcanic eruprions, wildfires, grasshopper and locusr infesrarions, droughr and deserrificarionand orher calamiries of narural origino

Ar rhe inrernarional level, rhe arrangemenrs involve a Special High LevelCouncil, a Scienrific and Technical Commirree and a Secrerariar for rheIDNDR. This framework relies heavily on measures to be raken ar narionallevel and all governments are called upon to formulare narional disasrermitigarion programmes. Today, rherefore, rhe srudy of hazards is veryrelevanr ro public policy in many countries. Ar rhe same rime, ir is equallydifficult to forecasr rhe degree of success rhar rhe Decade will have achievedin reducing hazards worldwide by rhe year 2000. This is because rheIDNDR is a conrinuously evolving programme rhar reflecrs rhe rensionsand conflicrs rhar will always surround rhe assessment of risk and rhereduction of hazard in rhe environment.

HAZARO ANO RI5KHazard is an ever-presenr, inescapable part of life. Each day we all faceSorne degree of personal risk, wherher ir be to life and limb in a roadaccidenr, to our possessions from rhefr or carelessness or to our immediaresurroundings from noise or orher rypes of pollurion. No one can live in

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THE NATURE OF HAZARDa tatally risk-free cnvironment and a concern for risk can be traccd backto the earliest recorded times (Covello and Mumpower, 1985). Moreover,it is expectcd that public concern about risk will cominue to increase inthe future despite the fact that most people are enjoying longer, healthierlivcs.Risk is sometimes taken as synonymous with hazard but risk has theadditional implication of the chance of a particular hazard actually occurringo Thus, we may define hazard as 'a potemial threat ro humans andtheir welfare' and risk as 'thc probability of hazard occurrence'. Thedistinction was neatly illustrated by Okrent (1980), who considered twopeople crossing an ocean, one in a liner and the other in a rowing boatoThe hazard (death by drowning) is the same in both cases but the risk(probability of drowning) is very different. If the drowning actuallyoccurred, it could be called a disaster. So a disaster may be seen as 'therealisation of hazard'.

Clearly, hazard, risk and disaster operate on varying scales. In terms ofdecreasing hazard severity, we can recognisc the following threats:1 hazards to people - dearh, injury, disease, stress2 hazards to goods - property damage, economic loss3 hazards to environment - loss of flora and fauna, pollution, loss ofamenity.Just as hazard can bc ranked, so the probability of an event can be placedon a theoretical scale from zero to ccrtainty (O to 1). The relationshipbetween a hazard and its probability can then be used to determine theoverall degree of risk, as shown in Fig. 1.1. Whilst damage to goods andthc environment can be extremely costly in economic and social terms, itis normally accepted that a direct threat to life is the most serious hazardfaced by humans.

Given this framework, what is the risk from environmental hazard in atypical developed coumry (DC)? Taking the UK as an example, Grist (1978)has shown that about 640,000 deaths occur each year from all causes in thetotal population of sorne 54 million. This yields a figure of 1.2 x 10-2 asthe individual risk of death per year averaged over the population. Table1.1 shows that thc risk is strongly age-dependent. Ir is high during the firstfour years of life, drops markedly for the 5 to 9 age group and then risessteadily so that, at age 70, individuals are exposed to a risk approximatelyten times that of the youngest children. This pattern reflects the imponanceof degenerative diseases in the Western world. About 90 per cent of al1deaths are due to familiar medical disorders (heart disease, cancers, rcspiratory ailments). Accidental death constitutcs less than 3 per cent of the overal1risk and is mostly attributable to common events, such as road accidents.Therefore, the high media profile for rapid-onset environmental disastersis not matched by the actualloss of life in the DCs.

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H A Z A R D I N T H E E N ~ R O N M E N T Hazard -low --igh

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Ienvironment

::;:::==goods

:::>'life

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>-:Cl3..ce l 1)..c (JFigure 1.1 Theoretica1 relarionships between the severity of environmenral hazard,probability and risk. Hazards to human life are rated more highly rhan damage toeconomic goods or the environment.Source: After Moore (1983)

rabIe 1.1 Individual risk of dearh (aH causes) according ro agefor the UKAge group Individual risk per year(x 10 3)

0-4 3.35-9 0.310-14 0.315-19 0.620-24 0.725-34 0.835-44 1.845-54 5.855-64 14.865-74 36.775-84 87.785 plus 205.2Source: After Grist (1978)

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THE NATURE OF HAZARDTable 1.2 Majar disasters that hit the headlines in the USA(Magnitude refers to deaths per event)

Event type Time period Magnitudelv!aximum Average FrequenC)'(events/year)Air crashes 1965-1969 155 78 6.00Earthquakes 1920-1970Explosions 1950-1968Majar fires 1960-1968Flaads (tidal 1887-1969waves)Hurricanes 1888-1969Majo r rai1 1950-1966crashes

180,000100322900,00011,00079

25,000263528,000

1,10530

0.502.000.670.540.411.00

Majar marine 1965-1969accidents-300 61 6.00

Source: After Starr (1979)

The main reason is that, although major disasters may be importantincidents for group deaths, they occur relatively infrequent1y. Table 1.2,abridged from Starr (1979), details sorne natural and man-made disasterswhich made headlines in the United States press. Ir can be seen that theevent frequency (last column based on differing runs of years) is low. Onthe other hand, the fatal consequences, especially for certain natural hazards events, can be very high. An inventory compiled for involuntary (i.e.accidental) risks by Dinman (1980) and presented in Table 1.3 shows thatthe threat in the USA from sorne natural hazards (flood, earthquake,tornado) is likely ro be larger than that associated with sorne man-madeand technological accidents (releases from an aromic power station).Although environmental hazards are not an everyday cause of death ordamage, it is their potential for unexpected catastrophic loss which notonly ensures that they make news but also gives them their distinctivecharacter.

WHAT ARE ENVIRONMENTAL HAZARDS?The definition of environmental hazards is difficult. Most previous attention has been given ro natural hazards, defined by Burton and Kates(1964a) as 'those elements of the physical environment harmful ro Manand caused by forces extraneous ro him'. Traditionally, natural hazardshave also been seen as 'Acts of God'. This perspective has not been helpfulbecause it suggests that humans have no pa n ro play in creating thesehazards and have even less hope of mitigating them. However, with changing ideas of cause and effect, the concept of hazard has also changed. Ashuman influence - both deliberate and inadvertent - has spread over the

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HAZARD IN THE ENVIRONMENTTable 1.3 Risk of death from involuntary hazards

Involuntary risk Risk 01 death/person/yearStruck by automobile (USA) 1 in 20,000Struck by automobile (UK) 1 in 16,600Floods (USA) 1 in 455,000Earthquake (California) 1 in 588,000Tornadoes (Midwest) 1 in 455,000Lightning (UK) 1 in 10 mil1ionFal1ing aircraft (USA) 1 in 10 mil1ionFal1ing aircraft (UK) 1 in 50 millionExplosion, pressure vessel (USA) 1 in 20 mil1ionRelease fram atomic power stationAt site baundary (USA) 1 in 10 mil1ionAt 1 km (UK) 1 in 10 millionFlooding of dike (Netherlands) 1 in 10 mil1ionBites of venomous creatures (UK) 1 in 5 mil1ionLeukaemia 1 in 12,500Influenza 1 in 5,000Meteorite 1 in 100 billionSource: After Dinman (1980)

globe, it has become progressively more difficult (and point1ess) to attempta rigid distinction between Acts of God and Acts of Man. For example,flood problems may be exacerbated both by natural fluctuations in climateand by human activities such as land drainage, river channelisation anddeforestation. Equally, most hazards have both natural and technologicalcomponents. The impact of a tropical cyclone can be great1y reduced bymeans of a warning message derived from moniroring by satellites andweather radar. The impact of a nuclear accident will be heavily influencedby the prevailing weather conditions controlling the downwind path andthe rate of fallout from the radioactive plumeo

Natural hazards are best seen in an ecological framework (Fig. 1.2). Thisdistinguishes between natural events and their interpretation as naturalhazards (or resources). Since the Earth is a highly dynamic planet, mostnatural events show a wide range of variation through time in the use ofenergy and materials for environmental processes. The outer limits of thisbehaviour we call extremes and cenain statistical measures, notably magnitude-frequency relationships, are used to describe such extremes. Butextreme natural events are not considered hazards unless they cause death?r damage ro humans. Asevere earthquake in a remote, u npopulated regionIS an extreme natural event, of interest to seismologists, and no more.

Natural hazards, therefore, result from the conflict of geophysical processes with people and they lie at the interface between what has beencalled the natural events system and the human use system. This interpretation of natural hazards gives humans a central role. First1y, through

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THE NATURE O f HAZARD

lesources I Hazardsr e s ou r c e s ~ Response Iatural events

system

II

Human us e Isystemt

Figure 1.2 Environment al hazards exist at the interface between the natural events andhuman use systems. Human responses to hazards can modify both the natural eventsin, and the human use of, the environment.Source: After Burton, Kates and Whi te (1978)

location, because it is only when people and their possessions get in theway of natural processes that hazards existo Secondly, through perception,because humans place value judgements on natural processes as pa n of ageneral environmental appraisal whenever they settle and use land. In otherwords, hazardous events merely represent the extremes of a distribution ofprocesses that, in a slightly different context, would often be regarded asa resource (Kates, 1971).This situation is illustrated in Fig. 1.3 (Hewitt and Bunon, 1971). Theshaded zone represents an acceptable range of variation for the magnitudeof the physical variable which is bounded by upper and lower damagethresholds. The physical variable can be any environmental element relevant ro human survival, such as rainfal!. Most social and economic activitiesare geared to sorne expectation of the 'average' conditions. As long as thevariation of the environmental element remains fairly close ro this expectedperformance, insignificant damage occurs and the element will be perceivedas beneficia!. However, when the variability exceeds sorne thresholdbeyond the normal band of tolerance, the same variable starts to imposea stress on society and becomes a hazard. Thus, very high or very lowrainfall will be deemed ro create a flood or drought respectively. Theexceedance of a damage threshold immediately enables two basic dimensions of a hazard ro be identified. First1y, the hazard intensity is determinedby the peak deviation beyond the threshold on the vertical scale. Secondly,

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HAZARD IN THE ENVIRONMENT

.... Upper extremee Hazards L [ ) a n 1 ~ ~ ~ t ~ ~ e ~ ~ o ' ? - - . . .

Q) ResourcestQ .-.?SmswIr..'. ; OamagethreshoICiJ .>- Lower extreme Hazardsa.Time

AverageBand of tolerance

Figure 1.3 Sensitivity to environmental hazard expressed as a function of thevariability of geophysical elements and the degree of socio-economic tolerance.Within the band of tolerance, events are perceived as resources; beyond the damagethresholds they are perceived as hazards.Source: Modified from Hewitt and Burton (1971)the hazard duration is determined by the length of time the threshold isexceeded on the horizontal scale.

In practice, there is only a fine line between resources and hazards, e.g.between water Ou t of control (flood hazard) and water under control(reservoir resource). Snow is a resource if it falls on the ski slopes but isa hazard if it falls a few hundred metres away on the access roads. Theatmosphere is considered 'benign' when it produces holiday sunshine but'hostile' when it produces damaging storms. In reality, the environmentis neither benign nor hostile. Ir is 'neutral' and it is only human location,actions and perception which identify resources and hazards within therange of natural events (Burton et al., 1978). Thus, human sensitivity toenvironmental hazards represents a combination of:1 physical exposure - reflecting the range of natural and technological

events and their statistical variability at a particular location, and2 human vulnerability - reflecting the breadth of social and economictolerance available at the same site.Ir follows that the risk from a specific hazard may vary through timeaccording to changes in either (or both) physical exposure or humanvulnerability. Sorne possibilities which give rise to increased risk are shownschematically in Fig. 1.4. Case A represents a constant band of tolerance~ n Constant variability but a decline in the mean value (perhaps a decrease1l l temperature). Case B represenrs a constanr band of tolerance and conS t ~ n t mean but an increased variability (perhaps a trend ro greater fluctuatlOns in annual rainfall). Final1y, in case C the physical variable does not

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e - igure 1.4 A schematic illustration of changes in human sensitivity to environmentalhazard due to variations in physical events and socio-economic tolerance. In each casethe risk of disaster increases through time.Source: After de Vries (1985)change but the social band of tolerance narrows (perhaps because population growth places more people at risk).

Human populations are most vulnerable on the margins of tolerancewhere small physical changes may create large socio-economic impacts.However, the threshold may well be a narrow transition zone rather than asharp boundary and it is most unlikely that the relationships between eventintensity and hazard impact will be linear once the damage threshold hasbeen crossed. Over a long period of time, frequent bu t unpredictable lowlevel variability around a very critical threshold may well be more significantthan the occurrence of either isolated, or more predictable, extremes. Forexample, weather thresholds of economic and social significance can occurin the middle of a range of variation. Thus, QOC is a critical threshold becauseof the freezing of water at that temperature. In turn, ice on highways is mostslippery around QOC when the skid resistance may be lowered by a layer oflubricating water, and more road accident deaths are likely to occur in thismarginal situation than in much lower temperatures. But, in most midlatitude winters, such a value could hardly be described as extreme.

The tendency towards admitting more human responsibility for 'natural'hazard is due to several factors. On e factor has been the increased attention

HAZARD IN THE ENVIRONMENTgiven to all forms of environmental pollution which was described as a'quasi-natural' hazard by Burton and Kates (1964a). Another factor has beenthe radical reinterpretation of natural hazard in the Third World, which isexplored more fully in Chapter 2. Most important of all, it is recognised thattechnological hazards constitute a new kind of threat. Early concern wasassociated with the nuclear and space programmes in the developed worldbut the risks now extend to less developed countries (LDCs) as technologytransfer grows. Ir is conventional to see this threat as originating in sornefailure of technology, often associated with an element of 'human error'.Miller and Fowlkes (1984) have challenged this view, arguing that the term'technological disaster' renders such events impersonal in origin in a wayanalogous to the now out-dated concept of 'natural disaster'. They believethat such 'accidents' are due mainly to an excessive priority with industrialprofits and advocate the term 'man-made disaster'.

The term 'environmental hazard' has the advantage of including bothnatural and human dimensions. It also implies a spectrum of hazard types,as indicated in Fig. 1.5. This shows that hazard origins range from largely

Natu ra l Manmade

I nvo lun ta ryear thquake I n tense

tsunamicyc lone

volcanic eruptiontornado

avalanchef lood

droughtbushlire

t ranspor t accidentsindustrial explosions

water pollutionradioact ive la l lou t

civil riotlood add i t ives

smokingVo lun ta ry I mounta ineer ing I

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THE NATURE OF HAZARDnatural to largely man-made. Sorne attempt can also be made to scale therange of hazards according to whether the impacts are intense and local,or diffuse and widespread within society. The extent to which hazards arevoluntary or involuntary is very important. The voluntary nature ofhazard, expressed in terms of the degree of individual human responsibility, increases greatly from the essentially accidental, geophysical hazards(earthquake, tsunami) to the largely self-induced social hazards (smoking,mountaineering).

The great breadth of possible hazard identification has led to sorneimpossibly wide definitions of environmental hazard, e.g. 'the threat poten-tial po sed to man or nature by events originating in, or transmitted by,the natural or built environment' (Kates, 1978). This definition can includeboth long-term environmental deterioration (acidification of soils, buildup of atmospheric carbon dioxide) and all the social hazards, both involuntary and communal (crime, terrorism) as well as voluntary and personalhazards (drug abuse, mountain climbing). Table 1.4 provides a checklistof the many potentially hazardous environmental agencies or processeswhich may affect society. These hazards have such different origins andimpacts that a more focused and manageable definition is required.

In this book, environmental hazard will be mainly restricted to events !which directly threaten human life by means of acute physical or chemical 1trauma. As indicated by Sagan (1984), the deaths and injuries associated!with acute trauma are treated primarily as safety issues. This means thatthey produce quite different responses from human illnesses resulting fromchronic low-dose exposures to toxins, which are treated as health issues.Acute bodily trauma, plus any related damage to property or the environment, usually follows the sudden release of energy or materials in concen- Itrations which are greatly in excess of normal background levels. Suchreleases may come from a natural source, like a volcano, or from a manmade source, such as a chemical factory.

Any manageable definition of environmental hazards will be both arbitrary and contentious. But, despite their diverse sources, most acute trauma ihazards have a number of common features:1 The origin of the damaging event is clear and produces characteristiceffects, e.g. a flood causes death by drowning.2 The warning time is normally short, i.e. the hazards are often known',

as rapid-onset events, although drought is an important exception.3 Most of the losses, whether to life or property, are suffered very shortlyafter the evento4 The risk of exposure is largely involuntary, normally due to the location

of people in a hazardous area.5 The resulting disaster occurs with an intensity and scale that justifies anemergency response.

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HAZARD IN THE ENVIRONMENTTable 1.4 Potentially hazardous environmental agencies or processes

AtmosphericSingle element Compound hazardsRain Rain and wind stormsFreezing rain ('glaze') 'Glaze' stormsHail ThunderstormsSnow Tornadic storms and tornadoesWind HurricanesLightning BlizzardsTemperature: 'heat wave', 'Whiteout''cold spell', frostFog DroughtHydrologicFlooding: Riverine (rain, snowmelt, natural dam-burst floods)Lake and sea-shore wave actionWaterloggingSea-ice and icebergsRunoff droughtGlacier advanceGeologicMass-movemems: landslides, avalanches, mudflows, subsidence, etc.Erosion (foundations, soils, etc.)Silting (dikes, rivers, harbours, farmland)EarthquakesVolcanic eruptionsShifting sandsBiologicSevere epidemics in humansSevere epidemics in plamsSevere epidemics in domestic and wild animalsAnimal and plant invasions (e.g. locusts)Forest and grassland firesTechnologieTranspon accidentsIndustrial explosions and firesAccidental releases of toxic gasN ~ c l e a r power plam failuresFallures of public buildings or other structuresGenn or nuclear warfareSource: Modified after Hewitt and Burton (1971)!he approach ado pted here is not meant to imply that other environmentalproblems, which are influenced by human activity and are sometimes

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HAZARD IN THE ENVIRONMENTTHE NATURE Of HAZARDregarded as hazards, such as deforestation, desertification, depletion of thestratospheric ozone layer and rising sea levels resulting from the greenhouse effect, are unimportant. But these are comparatively long-termissues, sometimes of obscure origin and consequence. Environmental pollution rarely poses an immediate threat to human life on a catastrophicscale. Smets (1987) c1aimed that, apart from three industrial disastersinvolving the concentrated release of very toxic substances (mercury atMinamata, ]apan, in 1956; methyl isocyanate at Bhopal, India, in 1984and radioactive material at Chernobyl, USSR, n 1986) no nstance ofaccidental pol1ution had so far direet/y caused more than 50 deaths anywhere in the world.

From this broad distinction b etween environmental hazards and environmental problems, it is possble to derive the fol1owing working definitonof environmental hazards:

extreme geophysical events and major technological accidents, characterised by concentrated releases of energy or materals, whch posean unexpected threat to human life and can cause significant damageto goods and the environment.

Sorne links between rapid onset and longer-term threats cannot be denied.For example, earthquakes and landsldes are preceded by the slow buldup of stress in rocks and ground surface materials. Equally, sorne of thelonger-term trends towards envronmental deterioration will exacerbatethe damage potential of sorne existing hazards. Thus, it is predicted thatglobal warming during the next few decades, driven by radiatively activegases in the atmosphere, will raise sea surface temperatures. In turn, this'greenhouse effect' may increase the disaster threat from tropical cyc1ones.According to Emanuel (1987), the enhanced sea surface temperaturesassociated with a doubling of the present atmospheric concentrations ofCOz could raise the maximum destructive potental of these storms by asmuch as 60 per cent in sorne parts of the world. Rising sea levels, alsoassociated with global warming, wil1 increase the catastrophe potential forstorm surge in low-lying coastal communities. Desertification and unwiseland use contribute already to the impact of drought. In addition, theeffects of environmental hazards in the LDCs are often greatly compounded by prolonged economic and social difficulties.

It must also be admitted that certain disasters are so complex in origin,and compound in their effects, that they defy categorisation. Fo r instance,the famine of 1979-81 in the Karamoja region of U ganda was widelyattributed to drought. Yet the semi-nomads of this area have survivedperiodic droughts in the past rather well through a variety of traditionaladjustments. In this incident a failure of the rains was greatly complicatedby the collapse of the Ugandan economy, including the destruction of therural marketing and distribution network, civil strfe, which was magnified

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by the unusual availability of automatic weapons, and a major outbreakof cholera.Sorne choices in this book were arbitrary. Thus, hail and frost hazards

are inc1uded, although they rarely create major loss of life, largely becauseof the substantial economic damages which resulto In this context it shouldbe remembered that drought, which appears such a self-evident environmental hazard, is no t a life-threatening event in the developed world. Inview of the balance of previous work, and the availability of lterature,the emphasis will be on the impact of geophysical events and their management. Those readers wishing a definitive treatment of the physcal aspectsof such events, which draws heavily on theoretical mechanics and probability, are referred to Scheidegger (1975).

A TYPOLOGY OF HAZARD AN D DISASTERMost previous c1assifications of hazard have been dominated by geophysical processes. It has also been usual to identify the impact of singleelements, such as windspeed or rainfall, because this is relatively easy todo. In practice, most severe hazards arise from compound or synergisticeffects, as when wind combines with snow to produce a blizzard orearthquakes set off landslides in steep terrain. The volcanic eruption ofMount St Helens, USA, in 1980 led to earthquakes, ashfalls, landslides,floods and wildfires. Alternatively, natural hazards can be divided intothose of endogenous origin (such as earthquakes and volcanic hazards),those of exogenous origin (such as floods, droughts and avalanches) andthose of largely amhropogenous origin (such as floods caused by damfailure). Such classifications have advantages for the traditional organisationof scientific research but they are less useful for hazard studies.

Hazards can be grouped according to many other characteristics. Forexample, Hewitt and Burton (1971) considered a variety of factors relatingto damaging geophysical events which were no t process-specific including:1 areal extent of damage zone2 intensity of impact at a point3 duration of impact at a point4 rate of onset of the event5 predictablity of the eventoAlthough such c1assifications depend on rather poorly defined criteria,they have potentially more to offer than the causally-based c1assificationsfor modelling human response and organising hazard management.

More recently, Hohenemser et al., (1983) have viewed technologicalhazards as a sequence of events leading from human needs and wants tothe selection of a particular technology through to harmful consequences.This chain of technological hazard evolution can be employed more

17


11/17

THE NATURE Of HAZARDINITIAT-

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FOREIGNOVERN- GENCYUllOINSTAlLCHANGE fOCOMENT MEDICALUPRRIG-LIF' A1DACIION A1DRESERVESATlONSTYlE

I ' in... . . Figure 1.6 Schematic illustration of the causal chain of hazard development. The stagesare expressed generical1y at the top of each box and in terms of a sample droughtdisaster in the lower segmento Six potential control phases, designed to reduce disaster,are linked to pathways between hazard stages by vertical arrows.Source: Modif1ed from Hohenemser, Kates and Slovic (1983)widely, as il1ustrated fo r drought in Fig. 1.6. The top line indicates sevenstages of hazard development. The stages are identified generically at thetop of each box and in terms of a sample development of hazard in thebottom. The stages are linked by causal pathways denoted by triangles.Six control stages are linked to pathways between hazard states by verticalarrows. Each is described generically as well as by specific control actionsdesigned to eliminate or reduce the evolving hazard.Concentrated releases of energy or materials are likely to have complexconsequences fo r both environ mental and human systems. Rarely does a 'straightforward cause and effect situation apply. It is more usual to have acascade of impacts through environmental and social systems, e.g. frombiophysical through to economic impacts. Using the eruption of Mount StHelens again, this not only physical1y devastated an area of more than 500km2 but also had an ordered sequence of impacts on forestry (rangingthrough thrown trees, additional production costs and reduced income),and also impacted widely through Washington State affecting recreation,construction, retailing, insurance etc. This type of impact model should beseen in the context of the more general interactive hazard model (Fig. 1.2).Disasters are usually assessed on sorne quantitative criteria of death anddamage. Sheehan and Hewitt (1969), working with global nat ural disasters" 1defined a major disaster as causing:at least 100 people dead arat least 100 people injured arat least $1 mil1ion damageThis type of definition, stil1 in common use, is confined to losses andprovides a threshold rather than a scale. Despite its apparent precision, ithas important weaknesses. Although most people may be killed outright

18

lp, I S T A R V ~b? ATlON

HAZARD IN TH E ENVIRONMENTby an event, other deaths may result much later from disease or famine.Even if direct damage alone is considered, it is often impossible to costeconomic loss accurately and al10wances always have to be made for priceinflation through time. Great spatial differences in the wealth exposed todamage between the LDCs and the DC s mean that the arbitrary value of$1 mil1ion can represent very different levels of physical impacto Forexample, a $1 million loss would be caused by a much lower magnitudeevent in - say - California compared to Bangladesh. At the same time,California would be much more likely to have the resources to recoverfrom such a disaster. In the LDCs many disasters recur regularly simplybecause the underlying lack of resources precludes the necessary investment to introduce lasting solutions.

UNDRO (1984) defined a disaster more qualitatively as:an event, concentrated in time and space, in which a communityundergoes severe danger and incurs such losses to its members andphysical appurtenances that the social structure is disrupted and thefulfilment of al1 or sorne of the essential functions of the society isprevented.

This type of definition conveys a better idea of the social stress createdby a disaster, although no threshold or scale is given. It too concentrates onlosses and implies a major incident requiring the mobilisation of emergencyservices. In sorne highly localised incidents, such as a transport accident,the ratio of emergency service personnel to members of the public maywel1 exceed one. For a more widespread event, such as a hurricane, helperswil1 be outnumbered by victims and the effective response of the victimsthemselves, rather than the performance of the emergency services, is likelyto be the critical factor in mitigating loss.

Although community loss is the major characteristic of disasters, al1these definitions ignore the fact that, in virtual1y every disaster, sorne gainsalso arise. Therefore, it has become conventional to categorise hazardimpacts, not only into gains and lasses, but also into other effects (Fig.1.7). Direct effects are those first order consequences which occur immediately after an event, such as the deaths and damage caused by the throwingdown of buildings in an earthquake. Indirect effects may emerge muchlater and may be much less easy to attribute directly to the evento Theseinclude factors such as mental il1ness resulting from shock, bereavementand evacuation. Tangible effects are those to which it is possible to assignreasonably reliable monetary values, such as the replacement of damagedproperty. Intangible effects cannot be satisfactorily assessed in monetaryterms. The loss of human life, for example, has proved notoriously difficultto assess financial1y.

Direct lasses are the most visible consequence of disasters. They may becomparatively easy to measure but they are not always the most significant19


12/17

PhysicalDama,e taPraperty

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., TangibleI IntangibleFigure 1.7 The potential impact of environmental hazards in terms of losses and gains,both direct and indirect, with an indication of sorne tangible and intangible effects.

outcorne. They are caused by the immediate damage done to humans,goods and the environment.Direct gains represent the consequential benefits which may flow tosurviving residents in the area after a disaster. These can include variousforms of aid and even some longer-term enhancement of the environment,perhaps associated with fertile deposits from volcanic eruptions or riverflood processes. For example, on the Icelandic island of Heimaey, thevolcanic ash cleared from the town of Vestmannaeyjar was used as foun- 'dation material to extend the runway at the island's airport and to levelou t an old lava flow for a new settlement to replace the houses destroyedduring the eruption in 1973.

lndirect losses arise mainly through the second-order consequences ofdisaster, such as the disruption of economic and social activities in acommunity or the onset of ill-health amongst disaster victims. These effectsoften outlast those of the direct losses by months or even years and canbe highly intangible. There is a growing realisation that ill-health, bothmental and physical, is a major indirect effect of disaster.

lndirect gains are even less well understood. They are normally highlyintangible and represent the very long-term benefits enjoyed by a community as a result of its hazard-prone location. Very little systematicresearch has been undertaken, for example, into the balance between the 'continuing advantages of a riverside site (flat building land, good communi- 'cations, water supply and amenity) compared with the occasional losses lsuffered during periodic flooding.

20

THE NATURE OF HAZARD

Llass af lite o hs s afDestructian af 5 Business arArchaeala,ical 5 PraductianSite E,5 ,

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IIIness

HAZARD IN THE ENVIRONMENTHAZARD ASSESSMENT AN D RESPONSE

Any logical attempt to reduce environmental hazards depends on asequence of steps being taken by the relevant decision-makers. The firstrational step must be to identify the hazard and to estimate the risks basedon how often the event occurs and the likely consequences. This recognition phase rarely happens before at least one damaging event hasoccurred. Once the hazard has been identified, it is possible to adoptresponse strategies which may range from doing nothing at all to attempting complete control over the hazardous process. In practice, most strategies involve a mix of different responses aimed at some intermediateposition. If a hazard-reduction strategy is selected, it then has to beimplemented. Ideally, its effectiveness should then be monitored over time.Comprehensive hazard management, which involves both assessmentand response, can be seen to involve four chronological stages, althoughthe stages often over-lap. These stages operate as a closed loop because amajor aim of hazard management is to learn from experience and feedback.

Pre-disaster plannin g This covers a wide range of activities such as theconstruction of defensive engineering works, land use planning and theformulation, dissemination and maintenance of evacuation plans.2 Preparedness This stage reflects the degree of alertness immediatelybefore the onset of the hazard; for example, arrangements for emergency

warnings to be issued and the effectiveness with which public officialscan mobilise an evacuation plan.3 Response Another broad category dealing with events immediatelybefore and after they have happened, including reaction to warningsand emergency relief activities.4 Recovery and reconstruction These are much longer-term actlvltles

which attempt to return an area to normality after severe devastation.Such devastation can occur even in those areas apparently well preparedfor disaster after a major eventoStages 3 and 4 are often the most visible and can be illustrated in Fig. 1.8.The relief period covers the first few hours or days after the impacto Afterthe initial rescue of survivors, it is concerned with the importation of basicsupplies (food, water, clothing, shelter, medical care) to ensure no furtherloss of life. The rehabilitation phase involves the following few weeks ormonths during which the priority is to encourage the area to begin tofunction again, if only on a temporary basis. Temporary housing may beerected and the injured will be taken to regular hospitals as field hospitals~ l o s e down. Finally, reconstruction, often taking many years, occurs. This~ designed to put things back together permanently, if possible in anImproved formo For example, it might include the construction of a newflood control reservoir or the installation of a warning system.

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THE NATURE OF HAZARD

; ~

.- " C

Figure 1.8 5tages in the progressive restoratian of nonnality in an area following adisaster strike through rdief, rehabilitation and reeonstruetion aetivities.Source: After White and Haas (1975)

The learning benefits of experience for future hazard reduction strategywill be nullified if the level of human vulnerability to disaster continuesto rise fas ter than the degree of protection which can be offered. Theconcept of vulnerability implies a measure of risk combined with the levelof social and economic ability to cope with the resulting event in orderto resist major disruption or loss (Timmerman, 1981). In other words,vulnerability is the liability of a community to suffer stress, or the consequence of the failure of any protective devices, and may be defined as 'thedegree to which a system, or part of a system, may react adversely to theoccurrence of a hazardous event'. Societies can take many different attitudes to reduce vulnerability but these can often be seen as expressionsof either resilience or reliability.Resilience is a measure of the rate of recovery from a stressful experience.It can be defined as 'a measure of a system's, or part of a system's,capacity to absorb and recover from the occurrence of a hazardous event'.Traditionally, resilience has been the main weapon against hazard in theless developed countries (LDCs) where disaster is often accepted as arecurrent fact of life. Thus, nomadic herdsmen in semi-arid areas havetended to accumulate cattle during years with good pasture as an insuranceagainst drought. But increasing environmental degradation is creating amuch more fragile way of life for millions of such poor people.Reliability, on the other hand, reflects the frequency with which protective devices against hazard fail. It may be defined as 'a measure of asystem's, or part of a system's, ability to shield itself from the occurrenceof a hazardous event'. This attitude is more applicable to the industrialisedcountries (DCs) where there is a view that, through investment, technological advance and engineering design, the advanced nations have proofed

22

HAZARD IN THE ENVIRONMENTthemselves against environmental hazard. This belief exists largely becausethe high day-to-day reliability of most urban services conveys a false senseof security about the fundamental lifelines for food, water and energysupplies.But extreme stress, for example from an earthquake, can easily disruptroad networks, electric power lines or water pipes. This has very damagingconsequences because, when such systems fail, there is frequently noalternative source of supply. Unfortunately, the mistaken belief that commodities like communications, electricity and water will always be available, even in seismically active areas, means that programmes designed toimprove the hazard-prone reliability of such supply systems are widelyperceived to be unnecessary.

One further problem inherent in all responses to environmental fluctuations is that, the more a protective buffer is created against the smaller,shorter-term fluctuations, the more likely is this to sow the seeds ofdisaster when larger, longer-term fluctuations arise. Climatic variabilityand the Aswan High Dam in Egypt is a case in point. This structure hasproved to be an effective shield against year-on-year fluctuations in rainfalland a large population in Egypt has become dependent on it for irrigationand power supplies. But, during a period of long-term decrease in rainfall,all the climate-sensitive activity that has grown up around the dam willbe threatened. In hazard mitigation, protection against the frequent, smallmagnitude event holds no guarantees against the rarer, larger hazards.

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DIMEN5ION5 Of DI5A5TER

Social expect ationsOther problems ensue because of rising social expectations, particularly inthe DCs. People have become much more mobile in recent years and'!expect to be transported around the world in the minimum elapsed timeirrespective of adverse environmental conditions, such as severe weather.The same absolute security of service is expected by consumers from mostweather-dependent enterprises such as energy supply or water supply.Frequently the drive for efficiency and greater competition in commerceand industry has resulted in reduced manning and smal1er operating margins. In turn, these al10w less scope for an effective corporate response toenvironmental hazard.

Growing interdependenceFinal1y, it is c1ear that the growing interdependence of individuals, communities and nations means that disasters can affect others far outside theimmediate area of impacto Major disasters, such as the Sahelian drought,not only disrupt local economies, but also can bring shortages in neighbouring regions, create floods of international refugees and stimulate aidprogrammes to the extent that the repercussions of environmental hazardare now truly worldwide.

PARADIGMS OF HAZARDThe current unprecedented awareness of environmental hazard has exposed "sorne fundamental differences in hazard interpretation. Since about 1975a split has been apparent between the traditional 'behavioural' viewof hazard, which owes its origins to the influential North Americanschool of hazardologists, and the more recent 'structural' interpretation,which typical1y derives from workers with field experience in the Third World.

The behavioural paradigmSorne evaluation of natural hazard predates the seminal work of GilbertWhite. For example, Marsh (1864) demonstrated how human actions wereadversely changing the environment and showed how cnservation mighthelp to limit the damage. This fundamental1y ecological viewpoint was rediscovered in the USA in the 1920s by writers such as Barrows (1923)and was then applied in the 1930s by a generation newly aware of the

40

perils of soil erosion and floods. In 1936 the US Congress passed animportant Flood Control Act which designated the Army Corps of Engineers as the agency to carry out large-scale watershed management. Thisorganisation commenced an ambitious programme of engineering workst control flood waters and protect floodplain property, of which theTennessee Val1ey Authority scheme became one of the best known exampIes. The approach which began here characterised attitudes to environmental hazards for the next fifty years. ,

The behavioural view starts from the premise that geophysical extremesare the main cause of disaster. Since the blame was assumed to lie withnature, it appeared logical that the control and prediction of natural eventswould provide an effective cure. Such goals appeared to be both attainableand desirable in countries like the United States during the 1930s and1940s because of the confidence associated with the rapid growth in relevant scientific fields (meteorology, hydrology), demands for greater development of natural resources and the availability of capital for major engineering projects. The paradigm also recognised the exacerbating role playedby the victims themselves. In the DCs behavioural faults were attributedto the poor perception of hazards by both the responsible authorities andthe victims which, for example, al10wed settlement on floodplains to takeplace. Within the LDCs it was felt that disasters were compounded byirrational, il1-informed behaviour, such as deforestation for firewood orthe over-grazing of land to exhaustion. It was further believed that theuniversal consequence of disaster was a disruption of normallife reflectedin a breakdown of economic production and a failure of the social system.This lack of order was seen as a temporary interruption of stability in theDCs but regarded mainly as a function of the inherent lack of a stable,Western-style, system in much of the developing world.Based on this rather paternalistic diagnosis, a solution was sought in thepower of applied science and technology. A 'technical fix' approach wasoften advocated, especial1y in the more advanced Western countries, whilst,in the ful1ness of time, it was thought that the transfer of the appropriatetechnology to the LDCs would eventually solve their problems too. Inevitably, the emphasis on high technology led to a rather authoritarian organisational pattern. Gnly government-backed institutions had the financialresources and technical expertise needed to apply science on the scaledeemed necessary and had the power to reimpose order and rationalityafter a major disaster. The United Nations, in particular, sprouted a numberof agencies with interests in disaster miti gation inc1uding the UN Development Programme (UNDP), UN Environment Programme (UNEP) and theoffice of the UN Disaster Re1ief Coordinator (UNDRO).This dominant paradigm has been characterised by three thrusts (Hewitt,1983):

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THE NATURE OF HAZARD DIMEN5ION5 OF DI5A5TERAn emphasis on field monitoring and the scientific explanation of geophysical processes. This was aimed at the modelling and prediction Of\1damaging events and has employed advanced technical tools such as'radar and telemetry. 11!'

2 A commitm.ent to physical and ~ a n a g e r i a l control has ~ l s o been p r e s e ~ 1 t . / I ' Often the aIm has been to contam nature through envIronmental engm-I'eering works such as flood embankments or avalanche sheds. Ji

3 Another clear strand has been the formulation of disaster plans and':emergency measures. This role has often been given to the armed forces, lmainly on the assumption that only a military-style organisation can 1function properIy in a disaster area, but also because it underpins the'notion of the state reimposing order on a devastated community.

It has since been recognised that this paradigm, which still represents the idominant view, is an essentially Western interpretation of environmentalhazard which is rooted in materialismo It has been described by its criticsas an optimistic, deterministic evaluation which reflects undue faith intechnology and capitalismo The dominant view has also been criticisedbecause it over-exaggerates the role of the individual in hazards, either asa decision-maker or as a victim.

Th e structural paradigmSince the mid-1970s an alternative interpretation has been gaining ground.This view can be termed structuralist in approach because, contrary to the ,dominant hazard paradigm, it emphasises the constraints which are placedon individual action by broader and more powerful institutional forces.There is little doubt that an alternative philosophy was sought because'the earIier approach had no t proved wholly successful in reducing disaster,impact, especially in the LDCs. Indeed, the structuralist view has beenllargely developed by social scientists with first-hand experience in theThird WorId (Waddell, 1983).

This view forges a link between environmental disasters and the underdevelopment and economic dependency of the Third WorId. It originatesin the belief that disasters in the LDCs arise more from the workings ofthe global economy, from the spread of capitalism and the marginalisationof poor people than from the effects of geophysical events. Consequently,the proponents of this view argue fo r a clearer distinction between what ,]they see as the geophysical 'triggers' of natural disaster and the continuing,economic, social and political problems of these nations. It is a radical,Marxist interpretation of disaster which envisages solutions based on theredistribution of wealth rather than on the application of science andtechnology.

42

The alternative view challenges the behavioural paradigm at several keypoints:

It asserts that even natural hazards are no t uniquely dependent ongeophysical processes. In the LDCs especially, it is argued that growingpoverty has created greater vulnerability for the population either as arural proletariat (dispossessed of land and compelled to grow cash cropsrather than subsistence food) or as an urban proletariat (forced intoshanty towns in the most dangerous built-up areas). Thus, the severityof disaster impact is related more to the scale of human exploitationthan to the stresses imposed by nature.

2 It queries the assumption that disasters are such unusual phenomena ina Third WorId contexto This point stems from the fact that manydisasters occur in areas experiencing rapid environmental and socialchange. It is argued that physical processes creating cyclones or droughtshave existed for much longer than human activities, such as urbanisation,and more truly reflect the nature of such regions. That disasters regularIyrecur in poor countries is increasingly linked to the fact that the rangeof responses to combat them is severely limited.

3 Given a belief that disasters in the Third WorId are characteristic r2.!herthan accidental, and that their roots lie in the everyday social order, itfollows that the mitigation of hazard depends on structural changetaking place in society. In particular, such change should ensure thatlocal knowledge is tapped and eventually replaces a reliance on importedtechnology. Mitigation is best achieved from within, by changing theprevailing social and economic contexts, rather than by external applications. Technical aid and disaster relief, particularIy beyond the emergency relief phases, are perceived as often increasing, rather than reducing, vulnerability by making a short-term, local problem semi-permanentthrough additional dependency.

4 It asserts that disaster victims are no t to blame for their ow n misfortunes. They do not necessarily lack adequate perception or engage inirrational, hazard-inducing behaviour, but - especia lly in the ThirdWorId - they do lack the time to prepare for emergency action andthe resources to recover from disaster. Again, over-population and theattendant rise of hazard-prone primate cities are interpreted as a symptom of capitalism rather than as a cause of environmental disaster.

In summary, the alternative view is based on the theory that underdevelopment is no t a temporary state but is an ongoing, deliberate process ofThird WorId impoverishment perpetuated by technological dependencyand unequal trading arrangements between rich and poor nations (Susmanet al., 1983). Within the LDCs, it leads to the growing process of marginal

43


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THE NATURE OF HAZARD/ ~ - - .

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17/17

3RISK ASSESSMENT AND

PERCEPTION

THE NATURE OF RI5KRisk is an integral part of life. Indeed, the Chinese word for risk 'weij-ji' combines the characters meaning 'opportunity' and 'danger' to implythat uncertainty always involves sorne balance between profit and loss.Since risk cannot be complete1y e1iminated, the only option is to manageit. Risk management means reducing the threats to life, property andthe environment posed by hazards whilst simultaneously maximising any :associated benefits. A necessary first step is to obtain sorne assessment ofthe actual risks involved.Risk assessment, involving a re1iable quantitative measure of risk, should Iideally underpin all hazard management. In practice, the risk of disasterhas not yet been estimated for many hazards. Even when risk analysis hasbeen undertaken, great uncertainties usually attach to the estimateobtained. Risk itse1f is such a complex concept that a single, scientificallyrepeatable solution will rare1y satisfy all the political realities of thedecision-making process. Where possible, risk assessment is undertakenfirst to find out what the problems are. When this has been done, riskmanagement - the process of deciding what to do to mitigate the problems- takes overo It is wide1y accepted that hazard management is a broadtask, involving economics, legal standards and available technology in whatare often fine1y balanced judgements.

Risk assessment cannot be divorced from value judgements and choiceswhich, in turn, are conditioned by individual be1iefs and circumstances.Many people make decisions and take actions regarding hazards based ontheir personal perception of the risk rather than on sorne objective1yderived measure of the threat. Because of this, risk perception also has tobe regarded as a valid component of risk management alongside more "scientific assessments. Distinctions are frequently drawn between objectiveand perceived risks, large1y because people perceive risks very differentlyfrom the predictions made by the more objective assessment mode1s.Resolving the resulting conflict between the results of technical risk analy-

RISK ASSESSMENT AND PERCEPTIONsis and subjective risk perception is a major factor in most hazard management stratepes.The type and degree of risk varies greatly between individuals of thesame age and sex according to personal factors such as location, occupationand life-style. In view of this, it is common to classify risks into two maincategories: involuntary and voluntary.

Involuntary risks These are risks which are not willingly undertaken.They are often re1atively rare but typically have a catastrophic potentialimpact. The risk may be unknown to the exposed persono If the risk isperceived, it may not be seen as controllable. Most of the hazardsconsidered in this book fall into this category and represent the risksimposed as a result of living in a particular environmental or landscapesettmg.

2 Voluntary risks These are risks which are more willingly accepted bypeople through their own actions. Such risks are like1y to be morecommon, have less catastrophe potential and be more susceptible tocontrol. Unlike involuntary risks, they are rated more directly by individuals according to their own judgements and life-style. The greaterscope for control over voluntary risks is seen in either individualbehaviour (stopping smoking or ceasing participation in a dangeroussport) or sorne form of government action (the introduction of safetylegislation or pollution control). Man-made hazards, including risksfrom technology, are sometimes placed in this group.

This division is often less clear than it appears. For example, while cigarettesmoking or mountain climbing are obvious examples of individual voluntary risk-taking activities, the same cannot be so firmly stated for eitherdriving a car or certain occupational risks. Driving a c

Despite these problems, people do react differently to voluntary risks47

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Livro Environmental Hazards