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SchadenspiegelSpecial feature issueRisk factor of air
1/2008, 51st year Losses and loss prevention
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Dear Reader,
Air on the move is expensive for the insurance industry.
Windstorms can devastate whole regions and cause damage
costing billions. We have gathered together all you need to know
about this natural hazard in a special topic entitled Weather
phenomenon: Windstorm. We give you a picture of the loss
situation after Hurricane Wilma, which devastated the Mexican
holiday paradise of Yucatn in 2004 and led to business interrup-
tion losses whose adjustment was particularly tricky. And then
we show how arduous the salvage of a container vessel can be,
taking the example of MSC Napoli,which was stricken during
Winter Storm Kyrill in 2007.
The risk factor of air is not restricted to the windstorm hazard,
though. Cue: air pollution. Of the environmental media air, soil,
and water, it is the air that influences our physical well-being
most intensively. What about the expenditure for asbestos-
related occupational diseases or immission-related respiratory
diseases? And is air a friend to aviation or rather an incalculable
risk? We interview a pilot and aviation underwriter and find out
how dangerous turbulent air movements really are to air traffic.
Air can also catch fire. In this, the fourth and last special feature
issue in our series Water, fire, earth, air, our authors report
on the explosion hazard of combustible dust. They also address
the necessity of clean air in the production of semiconductors
and describe a defective wind turbine, whose rotor continued
turning at increasing speed until one of the rotor blades broke
off. Finally, this issue also contains our review of catastrophes
in 2007.
What do you think of this issue? Please write and tell us at:
Your Schadenspiegel team
Our publication portal at www.munichre.comis the place to go if you
wish to order past issues of Schadenspiegel since 2000 or download them
in pdf format.
Risk factor of air
Stormy, destructive,
dangerous
Editorial
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Renewable energyWhen the turning stopped:
Defective wind turbine
A rotor blade breaks off and is
wrapped around the nacelle.
Page 2
Fire risk
Dust explosions
When the air catches fire
Combustible dust threatens industry.
Page 6
Interview
Aviation risks
Wind shear and wake vortices
Modern technology makes aviation
risks manageable.
Page 14
Environmental risk
Air pollution and liability
Health risks from asbestos and
emissions.
Page 44
Special risk
Clean air in semiconductor
production
Why fire protection is so important
in this sector.
Page 50
Special topic:Weather phenomenon:Windstorm
Windstorm The most important
natural hazard worldwide
Loss prevention includes windproof
construction.
Page 19
Hurricane Wilma Adjustment ofbusiness interruption claims
How is compensation calculated?
Page 32
Winter Storm Kyrill MSC Napoli
Difficult salvage of vessel and
containers.
Page 38
Major losses in 2007Fires, aircraft accidents, natural
catastrophes.
Page 54
Readers letters
Page 57
Contents
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Renewable energy
When the turning stopped:Defective wind turbine
It was four months before a grave error made while servicinga 2.5-MW wind turbine developed into a spectacular loss. As sooften happens, it was the result of human error. The incidentnot only stopped operations abruptly but also made it necessaryto carry out lengthy and extensive repairs.
Authors
Winrich Krupp, Markus von Stumberg, Munich
A spectacular sight: one of the
turbines rotor blades wrappedaround the steel tower. Human
error and technical defects were
the cause of this loss.
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The wind turbine was part of a wind farm, where
twenty turbines were linked up together. All the
turbines had been working for about a year without
any particular trouble. So when the manufacturer
carried out a routine servicing job, there were no
adverse findings. But in the process of servicing
one of the 2.5-MW turbines, a serious error wasmade that was not detected at first.
The loss event
It was not until four months later that an unfortu-
nate confluence with other cases of negligence and
adverse circumstances led to the loss occurrence.
What had happened?
On the day of the loss, the wind farms automatic
monitoring system registered a malfunction in the
high-voltage underground cable linking the wind
farm to a switching station about 10 km away. Asplanned, it automatically shut down the turbines
and disconnected them from the grid.
Servo-motors turned the rotor blades into what
is known as the feather position. In this position,
the angle of attack is reduced to a minimum and
the rotors come to a standstill. Brakes were also
applied to secure the rotors in that position.
But the coordinated shutdown routine was only
performed by nineteen of the twenty turbines.
One of them failed to conform to the automatic
sequence and none of the rotor blades were turnedto the feather position. On the contrary, since
the wind turbine was disconnected from the grid,
the rotor turned at increasing speed, until finally
one of the three blades could not withstand the
pressure and centrifugal forces any longer. The
38-m fibreglass-reinforced plastic blade broke off
and was wrapped around the nacelle at the top
of the 80-m steel tower.
But that was not all. The unbalance caused by the
turning rotor and the resulting forces and torque
were transmitted through the tower to the foun-
dations. Owing to the comparatively high elasticityof the material, the steel tower was practically
undamaged, but numerous cracks were later dis-
covered in the concrete foundations. They were
damaged so severely that they had to be demol-
ished and rebuilt.
The rotor and the two remaining blades had to be
replaced, too. Repairs were possible, however, onthe nacelle, which accommodates the generator,
gears, and bearings.
Result: Besides causing property damage of
around 2m, the accident put the turbine out of
service for several months.
The cause
The operator and the manufacturer were equally
intent on investigating the cause of loss as quickly
and precisely as possible not least in order to
prevent the same thing happening again.
Analyses of all the recorded operating data, the
service log, the plant software, and further investi-
gations both on-site and at the manufacturers
factory showed without any doubt that the person-
nel had switched off the monitoring alarms for
the routine servicing job (maintenance work) on
the wind turbine conducted months ago but had
inadvertently failed to reactivate them afterwards.
This error had far-reaching consequences because
nobody noticed a deep discharge of the off-line
battery system that powered the servo-motors for
adjusting the blades angle of incidence.
Cracks in the concrete left
no alternative but to remove
the foundations and rebuild
them.
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This deep discharge was found to have been
caused by a faulty slip ring, which has the job of
supplying the battery charger with power, and a
corroded contact in the chargers wiring. Conse-
quently, the automatic plant control system could
not drive the rotor blades into the feather position
during the power outage.
Learning from experience
If the safety system had been fully activated, the
controls would have identified all the technical
deficiencies and would have shut down the plant
in good time. The damage to the turbine was def-
initely caused by the alarms being deactivated.
Even so, the turbine manufacturer responded in
exemplary fashion by introducing an array of
measures. The training of maintenance staff has
been further improved. Particular attention is nowgiven to providing them with even more in-depth
knowledge of the function and significance of the
safety systems. A change in the monitoring system
software will prevent the deactivation of crucial
alarms for such parameters as overspeed, vibra-
tions, temperatures, and battery status.
Additional safety is provided by stricter password
controls and more narrowly defined authority levels
in the operating software that are now needed to
bypass monitoring and safety devices. Last but not
least, a remote query system automatically checks
the monitoring system for full operational capabilityon a daily basis.
Conclusion
There is no doubt that manipulation of monitoring
and control systems whether during commission-
ing or in the operating phase always jeopardises
the safety of technical plant and equipment. When
there is no alternative to shutting down such sys-
tems, a maximum of care, knowledge, and reliabil-
ity on the part of the personnel responsible is
essential, because it is precisely this emergency
situation that often result in enormous losses.
Table 1 The components of a wind power plant
and the most frequent causes of loss
Source:
German Insurance
Association (GDV),
Berlin
Bearings and shafts
Wear and tear
Fatigue and cracks
Electric generator
Damaged windings
Asymmetry
Overheating and fire
Gearing
Worn teeth
Misalignment
Overloading
Eccentricity
Lubricant
Rotor blades
Lightning stroke
Ice load
Fatigue and cracksUnbalance
Tower
Vibrations
Fatigue and cracks
Way ahead of the rest:
Germany leads the field with
a total installed capacity of
22,247 MW. Further develop-
ment of the offshore segment
may also have a positive
effect on the proportion of
energy generated by the
wind.
Source: Global Wind Energy
Council (GWEC), Brussels
Fig.1 Top five countries: Installed capacity in 2007
Germany
United States
Spain
India
China
22,247 MW
15,145 MW
8,000 MW
6,050 MW
16,818 MW
0 5,000 10,000 15,000 20,000 MW
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Wind sector on the up
But the loss potential is increasing
Schadenspiegel team
The total installed capacity of wind power plants in
the EU is currently in excess of 48,000 MW, repre-senting an increase of 300% in the European mar-
ket over the past five years. The fierce competition
among manufacturers has led to a continuous
increase not only in the number of plants but also
in the size and performance of the turbines.
Whereas European plants had an installed capacity
of less than 200 kW on average in 1992, the figure
for newly installed plants in 2006 was 1,800 kW.
Wind power is a risky business for the insurance
industry. Defective gears, overheated generators,
and worn bearings material fatigue and inad-
equate reliability of service and maintenance are
the main causes of losses. The higher their per-formance, the more vulnerable the plants become.
What is more, in such a young class of business,
practical experience values only go back a few
years. But it is already certain that the costs of
settling machinery and machinery loss of profits
claims for wind farms will go on rising in the coming
years.
In order to keep losses to a minimum, more time
must be invested in the development and testing
of new plants, and higher quality standards are
needed for manufacture, maintenance, and repairs.
In addition to a detailed and comprehensive riskassessment, insurers must encourage loss preven-
tion and loss avoidance. Service and maintenance
clauses should be an integral part of each insurance
contract and should specify how often the main
components are to be replaced or overhauled.Fig. 2 Schematic structure of wind turbine
Wind energy is converted into mechanical rota-
tional energy with the aid of rotors. Once used
directly by windmills for purely mechanical uses,
this energy is nowadays used to drive generators
that produce electrical energy.
The nacelle houses the hub, gearing, and gener-ator on the horizontal rotor shaft. It is turned to face
the wind and ensures that the rotor takes optimum
advantage of the prevailing wind conditions.
Incidentally, the operation of wind farms only
makes technological and economic sense if the
wind reaches what is called the start-up wind
speed.
Hub, shaft,
and blade
pitch
mechanism
Rotor blade
Rotor locking brake
Gearing
Electrical
switchgear and
control system
Nacelle
Electric generator
Tower
Transformer
Rotor shaft
Foundations
Diagram: Munich Re
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Fire risk
Dust explosions When the air catches fire
It is estimated that not a day goes by in Europe withouta dust explosion. According to a current study fromthe United States, combustible dust represents a dangerin any industrial facility given an adequate concentrationin the air and an ignition source. The explosive mixcosts insurers millions of euros.
Author
Dr. Alfons Maier, Munich
Large-scale fire at Hayes Lem-merz International, a vehicle
components supplier: an alu-
minium dust explosion was fol-
lowed by a fireball with extremely
rapid fire development.
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The fact is that the smaller the particles and the
finer their distribution in the air, the greater the
explosivity of combustible dust. The ignition
source may be no more than a small electrical dis-
charge triggered by a plug being removed from
a socket or a hot metal component.
Dust explosion is a familiar hazard particularly
in the woodworking, metalworking, plastics
processing, chemicals, paper, agricultural, food,
and fodder industries. Precautions are taken to
prevent such events from occurring, and many
facilities go on producing for years and years
without any mishap.
Statistics on dust explosion losses
In spite of all the precautions taken, the agricul-
tural and food industries are particularly known
for large losses and a certain loss frequency.Although large individual losses regularly occur
in other industries, too, meaningful statistics are
compiled and maintained only for individual fields
or branches of these industries and only for indi-
vidual countries. In most cases, it is almost impos-
sible to compare these statistics because they draw
on sources that differ in terms of the designation
and composition of dusts, facility types, and igni-
tion sources. In contrast, dust explosions in the
agricultural sector and coal dust explosions in
the mining industry, for instance are generally
well-documented.
What is a dust explosion?
In a dust explosion, a mixture of
dust particles ignites in the air. Forthis to happen, the particles must
consist of combustible material and
be smaller than about 500 m, and
their concentration in the air must lie
between the lower explosion limit
(LEL) and the upper explosion limit
(UEL). For many types of food dust,
the LEL is between 30 and 60 g/m3,
the UEL between 2 and 6 kg/m3.
In addition, oxygen and an ignition
source with a sufficient supply ofenergy must be present.
A distinction is made between pri-
mary and secondary dust explosions.
When a dust suspension in a con-
tainer, room, or system component,
for example ignites and explodes,
we speak of a primary dust explo-
sion. In a secondary dust explosion,
dust that has settled on the ground
or on other surfaces is stirred up by
the primary explosion and ignites.A chain reaction follows: the pressure
wave emanating from the secondary
dust explosion can stir up further
dust deposits and cause further dust
explosions.
Dust explosions in the US agricultural sector
In the dust explosion statistics of the US agri-
cultural sector there are records of
490 explosions from 1900 to 1956 with losses
of US$ 70m,
192 explosions from 1957 to 1975 with losses
of US$ 55m,
202 explosions from 1979 to 1988 with losses
of US$ 169m,
106 explosions from 1996 to 2005 with losses
of US$ 163m.
This averages out at about one event a month.
The annual number of events ranges from six to 18,
with individual loss amounts of between US$ 4m
and US$ 56m.
The long-term trend that emerges in the agricul-
tural sector is that dust explosions mainly occur in
elevators (e.g. chain or bucket elevators operating
as grain conveyors), fodder and flour mills, and
silos.
Documentation of dust explosions in Germany
The institute for occupational health and safety of
the German statutory accident insurance institu-
tions has analysed 599 dust explosions that
occurred in different sectors of industry over a
period of about 25 years up to and including 1995.
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Since 1785, when the first dust ex-
plosion was documented in a flour
warehouse in the Italian city of Turin,
explosions have occurred with regu-lar frequency and have lost nothing
of their destructive force throughout
this time. In 1977, for example, five
dust explosions occurred at US silo
facilities, killing 59 people and injur-
ing 49.
A flour dust explosion at the Roland
Mill in Bremen, Germany, in 1979
caused property damage equivalent
to US$ 50m, with 14 people killed and
17 injured. Later that same year, it
was the turn of a feedstuff factory inLerida, Spain, leaving ten dead and
a badly damaged silo plant.
Although the design of grain eleva-
tors has improved considerably over
the years, explosions continue to
happen with disturbing regularity.
In 1997, twelve people died in a grain
elevator explosion in Blaye, France,
with property and BI losses amount-
ing to about 23m. Only 16 of the44 elevator cells were still in their
original shape after the incident.
For safety reasons, however, the
remaining parts of the plant were
detonated as well.
In 1998, a mixture of dust and air
exploded in a large grain elevator
in Haysville, Kansas. Seven people
were killed and ten were injured,
with property and BI losses estimated
at several million US dollars. The
costs for rescue, fire-fighting, andsubsequent operations amounted to
about US$ 850,000.
A terminal at the port of Puerto
General San Martn, Argentina, was
the scene of a severe dust explosion
in a silo in 2001, which killed three
people and injured seven. There was
a further explosion at a port terminal
only a month later, this time in Para-
nagu, Brazil. In this case, one of thewarehouses was a total loss. The
force of the explosion flung 300-kg
chunks of concrete several hundred
metres through the air, with some
roof sections landing up to 1 km
away. The grain continued burning
for almost three weeks.
In 2002, a dust explosion which
occurred when a vessel was being
loaded with soy beans in the port of
San Lorenzo, Argentina, destroyed
the entire terminal. Three peopledied, 19 were injured.
The overview shows that
the facilities in which dust
explosions occur most fre-
quently are grain elevators
and hoppers. They account
for the largest proportion
of explosions particularly in
the wood and coal dust
groups (34.7% and 22.2%
respectively).
Review:
Major dust explosions in the agricultural and food industries
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Fire risk
Fig. 1 The facilities most frequently affected
in the various dust groups
Dust groups
Total
Wood products
Paper
Coal/Peat
Food and fodder
Plastics
Metals
Others
0 10 20 30 40 50
Silos and hoppers 19.4%
34.7%
25%
22.2%
26.9%
15.4%
44.1%
18.6%
Proportion (%)
Mills
Silos and hoppers
Mixing plants
Dust-removal facilities and separators
Conveyors and elevators
Silos and hoppers
Mills
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Fig. 1 shows the facilities most frequently affected
in the various dust groups (wood/wood products,
paper, coal/peat, food and fodder, plastics, metals,
and others). The most frequent ignition sources in
the various dust groups are the mechanical ones
(cf. Fig. 2).
New findings:
Combustible Dust Hazard Study
The Combustible Dust Hazard Study of the US
Chemical Safety and Hazard Investigation Board
(CSB) from the year 2006 was the first study to
incorporate losses from different sectors of indus-
try in one single examination. It shows that there is
an explosion hazard in all industries that handle
combustible dust.
The study included the sectors of food, rubber,
metal, wood, pharmaceuticals, plastics, paints andcoatings, synthetic organic chemicals, and other
industries that are not fully covered by the compre-
hensive safety regulations of the Occupational
Safety and Health Administration (OSHA). Agricul-
ture and coal mining were not included because
they are subject to the Grain Handling Facilities
Standards and the Mine Health and Safety Act
respectively.
Facilities like hospitals, the armed forces, research
institutes, and the transport sector were not con-
sidered either.
In the period from 1980 to 2005, 281 major dust
explosions are listed with a total of 119 dead and
718 injured, clearly showing that dust explosionsrepresent a major safety problem for industry.
People were injured or killed in as many as 71% of
the loss events in different branches of industry.
The explosions happened in 44 federal states and
involved a variety of materials. On average, there
were ten dust explosion events every year in this
period. More than half of the events were recorded
in the following sectors: food (25%), wood (15%),
chemicals (12%), and metal (8%). The dust explo-
sions were caused by wood dust (24%), food dust
(23%), metal dust (20%), and plastic dust (14%).
Source of Figs. 1 and 2:
Jeske, Arno; Beck, Hartmut:
Documentation of dust
explosions Analysis and case
studies (in German), Haupt-
verband der gewerblichen
Berufsgenossenschaften
(HVBG) (ed.), St. Augustin,
BIA-Report 11/1997.
The chart shows the most
frequent ignition sources
in the various dust groups.
Mechanical ignition sources
are the most common except
in the coal/peat group.
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Fire risk
Fig. 2 The most frequent ignition sources
in the various dust groups
Dust groups
Total
Wood products
Paper
Coal/Peat
Food and Fodder
Plastics
Metals
Others
0 10 20 30 40 50
32.7%
35.9%
50%
25.4%
35%
29.2%
30.8%
49.4%
23.7%
23.7%
Proportion (%)
Mechanical ignition sources
Mechanical ignition sources
Pockets of embers
Mechanical ignition sources
Mechanical ignition sources
Electrostatic discharge
Mechanical ignition sources
Mechanical ignition sources
Electrostatic discharge
Mechanical ignition sources
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Polyethylene dust exploded
at West Pharmaceutical
Services, Inc. The productionsection for pharmaceutical
products was completely
destroyed.
A series of phenol resin dust
explosions devastated the pro-
duction line at CTA Acoustics,
Inc. Substandard cleanliness was
one of the reasons why the resin
dust was able to ignite.
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Loss examples
Three large dust explosions in the United States in
the year 2003, with a total of 14 people killed and 81
injured, were among the reasons for the CSB carry-
ing out the Combustible Dust Hazard Study. On the
basis of the cases examined, it is possible to deter-mine some of the typical factors that lead to explo-
sion losses.
West Pharmaceutical Services, Inc.
Six people were killed when polyethylene dust trig-
gered an explosion at West Pharmaceutical Ser-
vices, Inc., Kinston, North Carolina, on 29 January
2003. The plant, which was completely destroyed
in the incident, produced rubber pharmaceutical
goods. The production process, which involved
dipping strips of rubber into a mix of polyethylene
powder and liquid and then drying them in air,
resulted in fine polyethylene dust being released.In line with the stringent hygiene requirements
applying to pharmaceutical enterprises, the pro-
duction area was cleaned regularly. Nevertheless,
fine combustible plastic dust accumulated above
the suspended ceiling. Eventually it ignited, result-
ing in a dust explosion.
Some of the staff had known about the deposits,
but they had not been sensitised to the dangers of
dust explosions. The material safety data sheet for
the polyethylene mix did not contain any warnings
about possible dust explosions either. What is
more, the companys safety review process failedto take into account the danger of explosion during
this stage of production.
Although the plant had been inspected by the
OSHA, the local fire authority, and insurance and
hygiene experts, the dust explosion hazard had not
been identified. The electrical lines in the ceiling
area were therefore not designed adequately.
The CSBs conclusion is that the explosion could
have been prevented or at least restricted if the
National Fire Protection Associations standards for
combustible dust had been observed. According topress reports, the insured loss totalled US$ 41m
(property: US$ 32m, BI: US$ 9m). West Pharma-
ceutical Services, Inc. was faced with further costs
in the million dollar range primarily in the form of
its deductible, investigation costs, legal expenses,
and environmental costs.
Fire risk
CTA Acoustics, Inc.
On 20 February 2003, a series of dust explosions
occurred at CTA Acoustics, Inc. in Corbin, Kentucky,
which produces insulation materials for the motor
industry. The outcome: seven people killed, 37
injured, and a devastated production facility. Dur-
ing production, fibre glass mats were impregnatedwith phenol resins. On the day of the explosion, a
tempering furnace was kept open because of a
problem with the temperature. Workers who were
cleaning the production area near the furnace had
probably stirred up combustible resin dust, which
immediately ignited. According to the CSB, the
dust explosion is very likely to have been due to the
design of the facility, working practices, and prob-
lems with on-site housekeeping. Moreover, the
production building was not designed to minimise
secondary explosions: the area of flat surfaces on
which dust can settle had not been reduced, for
example, and there were no fire walls separatingthe production areas from each other.
The CSB also found that the safety data sheet for
the used resin did not give a clear enough indica-
tion of the dust hazard. What is more, the compe-
tent authorities had not imposed any special
requirements regarding the dust explosion hazard,
nor had the fire protection authority inspected the
facility. The insurers had not recognised the danger
of the phenol resin dust exploding either.
In this case, too, the CSB concluded that if the
National Fire Protection Associations housekeep-ing standards had been observed and fire and
explosion barriers erected, the explosions could
have been prevented or minimised.
According to press reports, protracted negotiations
were followed by a jury assigning the main respon-
sibility for the explosions to the company supply-
ing the resin, obligating it compensate CTA Acous-
tics, Inc. for the sum of US$ 123m. The reasoning
behind the decision was that the supplier had not
provided adequate safety instructions for handling
the resin and had not drawn attention to the explo-
sion hazard.
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Hayes Lemmerz International
The third major loss occurred in Huntington,
Indiana, on 29 October 2003. In this case, it was
aluminium dust that exploded. One of the staff
was killed, several were injured. The explosion
occurred in the production area where cast alu-
minium and aluminium-based alloys for vehiclewheel rims are made. Aluminium scrap is crushed,
conveyed to the processing area, where it is
dried, and finally fed into the smelting furnace.
During the conveying and drying processes, com-
bustible aluminium dust is emitted into the air. The
dust is separated in a dust collector, and it is here
that the explosion probably occurred. The likely
explanation is that the collector had not been venti-
lated or cleaned sufficiently and was also too near
the processing area. The explosion propagated
through the exhaust-air ducts, finally producing a
large fireball that broke out in the furnace area.
The CSB ascertained that the dust collector was
not of dust-explosion-proof design. Furthermore,
no consideration had been given to the possibility
of dust explosions being transmitted along the
exhaust-air ducts. And there were other problems
as well. When the company had incorporated
the scrap-processing and dust-collecting system
into the existing facility, it had failed to implement
change management procedures. These might
have led to the danger being recognised. Further-
more, the dust deposits on the girder structure of
the manufacturing shop had not been removedand they triggered a secondary explosion, which
destroyed the shop roof.
Another failing was that the employees had not
been instructed on the dangers of dust explosions
due to aluminium dust, whilst the authorities had
not drawn attention to the dust explosion hazards
during past inspections.
Here again, the CSB came to the conclusion that
if the National Fire Protection Associations stand-
ards for combustible metals had been observed,
the explosion could have been prevented or atleast minimised.
Incidentally, the CSB recommends further research
into aluminium dust as a basis for long-term
improvements in the aluminium industry with
regard to dust explosion protection for dust separ-
ators.
Results: Combustible Dust Hazard Study
The Combustible Dust Hazard Study found that the
respective standards of the National Fire Protection
Association ought to have been observed in all of
these three cases. This alone can ensure that secur-
ity procedures are sufficient to reduce or even rule
out the risk of a dust explosion.
The factors leading to the damage in these three
large losses and in other cases examined by the
CSB include the following:
Facility management, official bodies, occupa-tional safety and health experts, and insurance
companies failed to identify the dust explosion
hazards and to recommend appropriate pro-
tective measures.
Housekeeping was inadequate. In most produc-
tion plants, there was an accumulation of danger-
ous, combustible dust.
Dust filters were not adequately designed to
withstand dust explosions or had not been given
proper maintenance.
Production processes were changed without a
sufficient examination of the possible dangers.
It is remarkable that, according to the CSB, only
about half of the safety data sheets for known com-
bustible materials are adequate sources of infor-
mation for users or employees on the dangers of
dust explosions. What is more, almost half (41%)
of the 140 safety data sheets for combustible dusts
did not contain a dust explosion warning. Only
seven made any reference to the National Fire Pro-
tection Associations standards on the prevention
of dust explosions.
The CSB study also contains a number of other
recommendations. These have already been taken
on board by the competent authorities in some
cases. It is to be hoped that their implementation
will gradually lead to improved dust explosion
protection in industry.
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Sources
Jeske, Arno; Beck, Hartmut:
Documentation of dust explo-
sions Analysis and case stud-
ies (in German), Hauptverband
der gewerblichen Berufsgenos-
senschaften (HVBG) (ed.), St.
Augustin, BIA-Report 11/1997.
Schoeff, Robert W.: U.S. Agri-
cultural Dust Explosion Statis-
tics, Kansas State University in
cooperation with FGIS-USDA,
20 March 2006.
U.S. Chemical Safety and Haz-
ard Investigation Board (ed.):
Investigation Report Combust-
ible Dust Hazard Study, Report
No. 2006-H-1, November 2006.
Fire risk
A recent dust explosion loss at
the production facility of a US
sugar manufacturer. Sugar dustis assumed to have exploded.
Conclusion
As far as the risk of dust explosion is concerned,
the insurance industry has so far concentrated
primarily on large losses in the agricultural and
food industries. However, the CSBs current study
makes it clear that all branches of industry in whichcombustible dust occurs are equally exposed.
The institute for occupational health and safety of
the German statutory accident insurance institu-
tions, the current Combustible Dust Hazard Study
published by the US Chemical Safety and Hazard
Investigation Board, and Munich Res loss experi-
ence all indicate one thing: the risk factors that lead
to dust explosions are similar throughout the
world. And they need to be given more attention
with a view to attaining effective loss prevention.
Otherwise, we must continue to reckon with further
deaths, injuries, and large property and BI losses.
The devastating explosion probably of sugar
dust at the Imperial Sugar Company in Port Went-
worth, Georgia, on 7 February 2008 shows that the
subject of combustible dust has lost nothing of
its topicality. Fourteen people were killed and a
number were injured. The damage is considerable.
Munich Re is certain that companies, authorities,
and insurance companies must now do more than
ever to ensure that dust explosion risks in industry
are identified, controlled, and minimised.
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Aviation risks
Wind shear and wake vortices
Air is a friend to aviation, countered Thomas Endriss,aviation underwriter and pilot, when we asked him aboutair as a risk factor in air travel. But we dig deeper: Andwhat about wind shear, wake vortices, and air pockets?
Interview
Thomas Endriss, Munich
The greatest risk in aviationis human error. Wind only
becomes dangerous when
it occurs unexpectedly
in the form of wind shear,
for example.
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Endriss: Although wind shear and wake vortices
can lead to problems, the main risk in aviation is
and remains human error. People make errors,
draw wrong conclusions, take incorrect decisions
and even the best technology offers no safeguards
against that. It is not usually one single cause that
leads to damage or accidents but rather a chainof events.
Schadenspiegel: So how dangerous is wind
shear, then?
Endriss: Its only dangerous when it comes un-
expectedly, when the wind changes direction very
suddenly, as during a thunderstorm, for instance.
Aircraft are now protected against this by wind
shear detection systems, which were introduced
about eight years ago. They measure the air
density using radar and give an acoustic warning
as soon as pressure conditions become abnormal.Modern cockpit systems can even supply visual
clues to the threatening danger from shifting
winds. By the way, most airports frequently
affected by wind shear have such safety systems.
Schadenspiegel: And what does the pilot have
to do then?
Endriss: Simply increase speed on approach to the
runway and come down at a higher residual speed.
Because whenever possible, aircraft are flown
into the wind for landing. If an aircraft has already
reached landing speed, say about 160 km/h, andis just about to touch down with 20 km/h of head-
wind, its speed will suddenly drop relative to air
motion as soon as the wind turns to 20 km/h of tail-
wind, for instance. The aircraft consequently
crashes because there is no more lift available.
Schadenspiegel: And what about during take-off?
Endriss: During take-off, the pilot can either wait
for the wind shear to subside or simply fly around
it with the help of modern technology. Air traffic
control or the cockpit instruments provide so-
called vectors to navigate aircraft around the dan-ger area. By the way, wind shear does not usually
represent any danger in-flight. An average passen-
ger jet flies at a speed of 850880 km/h, for exam-
ple, so that if the wind speed changes by 100 km/h,
the aircraft merely gets a bit slower or a bit faster.
The passengers do not notice anything at all, apart
from what might be a quite unpleasant shaking
of the aircraft.
Schadenspiegel: So technology makes wind shear
controllable. Can you give us any examples of
accidents happening in spite of this?
Endriss: Fortunately, there are only a few. One of
these happened at Toronto Pearson International
Airport in Canada on 2 August 2005. A brand-newAir France Airbus A340 was on approach to
Toronto during a huge thunderstorm, along with
many other aircraft. While the other aircraft con-
tinued to circle in holding patterns, the A340 pilot
decided to land, but approached at much too high
a speed. He presumably wanted to prevent the air-
craft from getting too slow because of the shifting
thundersqualls. Theoretically, as I just explained,
this was the correct thing to do. However, the tail-
wind was far from being as strong as expected. So
the aircraft touched down far too late and could not
stop on the wet runway. It rolled a further 200 m
into a ditch, broke in two, and burst into flames.Fortunately, all the passengers managed to escape,
and only a few of them had slight or minor injuries.
Schadenspiegel: And this again highlights the
critical role of the pilots. When you assess an air-
line, how important is their training for you?
Endriss: This is very important. As the number of
risks is very limited, with roughly 600 airlines
worldwide, personal contact plays a leading role.
When we inspect the airlines flight training centres
and simulators, their risk managers go along with
us. And we want to know how flight training isorganised. But we also talk about numbers and
about how the fleet will develop in the future
away from old aircraft, for example, and towards
top modern models with state-of-the-art cockpit
technology. And, of course, we inspect the aircraft
and maintenance facilities. What do the hangars
look like? Are they clean or cluttered up with all
sorts of things?
Schadenspiegel: And which Munich Re employees
are responsible for assessing the airlines?
Endriss: Our underwriters have different qualifica-tions, which all go to make up our expert know-
ledge. They come from a wide variety of profes-
sions, ranging from insurance specialists with a
pilots certificate and a maintenance licence to
aviation engineers and lawyers.
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Schadenspiegel: Let us come back to wind shear.
Do you also enquire whether early-warning
systems are on board?
Endriss: Of course, especially if we do not know
an airline well. And if we know that airports are
involved which are known for wind shear con-
ditions. But almost all airlines have wind shear
detection systems nowadays.
Schadenspiegel: At which airports is this particu-
larly important?
Endriss: One of the notorious airports is Dallas Fort
Worth International Airport in Texas, for example.
Denver International Airport in Colorado may also
be affected by wind shear because the Rocky
Mountains have a weather phenomenon similar
to the one we know in the Bavarian Alps: the foehn.
What is more, all areas are affected where heavy
precipitation can occur out of the blue. This is pri-
marily the case in the Far East, at airports in Singa-
pore, Malaysia, and Indonesia.
Schadenspiegel: What about airports like Santa
Catarina on the Portuguese island of Madeira?The landing strip is partially built on columns, on
a steep slope directly beside the sea.
Endriss: This airport is extremely difficult to
approach. Due to its position in the southeast of
a hilly island, the wind comes from the wrong
direction, so to speak, from northeast to north-
west. Because of the air masses being conducted
over a mountain directly next to the landing strip,
eddies are generated. The wind forms a kind of
rotor, right there where the landing strip is built.
What is more, until recently the airport only had
a relatively short runway, so that it was impossibleto approach at a higher speed. However, the run-
ways were extended in 2000, albeit with some
difficulty. Schadenspiegel even had a report on
this case, I believe.
Schadenspiegel: Yes, thats right: in the 2/2000
issue. Cracks had formed in the columns, leading
to an insured loss of about 1.4m.
Endriss: Even with the extended runway, though,
pilots are only allowed to land at this airport if they
have received special training on the simulator.
Lufthansa requires this training twice a year, for
example.
Schadenspiegel: Another question concerns wake
vortices. What are they exactly?
Endriss: Wake vortices are generated on the trail-
ing edges of the aircraft wings. Now how does
this happen? The form of the wings accelerates
the air streaming over their upper surface. This
results in negative pressure, which gives the air-
craft lift. The air flowing beneath the wings is not
accelerated as much. When the faster air from
the upper surface meets that slower air from the
lower surface, it produces turbulence. Vortices aregenerated at the wingtips and revolve like small
tornadoes, which get bigger and bigger as they
move away.
Schadenspiegel: Something like the rings you
make when you throw a stone into the water?
Endriss: Exactly. But wake vortices also produce air
resistance. This has recently led to the increasing
use of what are known as winglets, little turned-up
airfoils that are mounted on the wingtips. They are
not there for optical reasons, but to reduce the air
resistance. The result is that less energy is needed,and the aircraft uses less jet fuel.
Cross-section of a thunder-
storm cell producing strong
wind and hail. The arrows
in orange represent the air
streams, the thin black
arrows indicate the possible
tracks of hailstones. Wind-
storm damage and wind
shear may occur along the
squall line.
Source: Diagram based on
Kurz, Manfred: Synoptische
Meteorologie, Deutscher
Wetterdienst (ed.), Offen-
bach am Main, 1990
Fig. 1 Wind development during thunderstorms
Tropopause
Altitude (km)
km10
Updraught
regionDowndraught region
8 6 4 2 0 2 4 6 8 10
Squall line
Updraught
region
40C
0C
HailRain
10
5
Track direction
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Schadenspiegel: Do wake vortices pose a danger
to air traffic?
Endriss: Not to the aircraft that produces the wake
vortices but to the aircraft following behind. And
this is particularly the case during take-off and
climbing, since aircraft are much slower in thesephases than in the cruising phase and therefore
more susceptible to wake vortices. At cruising
speed, they are no problem at all. I only know of
one serious accident involving an aircraft that flew
into the wake vortices of another aircraft. This
was on 12 November 2001, when an American
Airlines Airbus A300 crashed over the New York
City district of Queens.
Schadenspiegel: What happened?
Endriss: It was a sunny, windless day, so the wake
vortices stayed put and were not blown away bythe wind as usual. There are standard routes that
aircraft have to adhere to during take-off, because
of noise protection regulations, for instance. So
the Airbus A300 used exactly the same route as
an aircraft that had taken off in front of it. Only a
little lower. As a result, it got into the wake vortices
of the preceding aircraft and went into an extreme
sideways roll. In such situations, the manufactur-
ers instructions specify exclusive use of the
ailerons, but the pilot, presumably on instinct,
attempted to counteract the roll using the rudder.
As it was not designed to cope with such a load,
however, the rudder broke. The aircraft went outof control and crashed. All the passengers were
killed.
Schadenspiegel: Another case of human
error, then.
Endriss: Im afraid so. It wasnt the wake vortices
alone that caused the crash. And the interval
between the two aircraft taking off was in line with
the regulations, too. There was simply an unfavour-able interplay of different factors: the weather,
wake vortices, and the pilots incorrect response.
Schadenspiegel: One last question: what effect
do air pockets have?
Endriss: I find this word amusing. Air is perman-
ently in motion. It rises when it is warmed up by
the sun and falls when it cools down, e.g. behind
clouds. To maintain altitude in these permanently
changing conditions, aircraft must fly contrary to
these air movements. However, if you fly from a
sunny area into a shady one, the air suddenly stopsrising and the aircraft loses height. All this happens
relatively fast and, due to mass inertia, the passen-
gers are lifted from their seats for a short time.
They feel like theyre falling into a hole.
Schadenspiegel: But has this ever made an
aircraft fall from the sky?
Endriss: No, never. And this has nothing to do with
turbulence either, which is more likely to result
in the aircraft shaking. Nevertheless, both as a pilot
and as a passenger, my recommendation is as
follows: if you are asked to fasten your seat belt,then please do so. In this way, you can be sure that
nothing will happen, even if the plane gets into
heavy turbulence or air pockets.
Wake vortices are generatedon the trailing edges of the
wings. The vortices at the
wingtips rotate like small tor-
nadoes, getting bigger and
bigger as they move away.
They can become dangerous
particularly for following air-
craft in the take-off or climb-
ing phase.
Fig. 2 Wake vortices
Diagram: Munich Re
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Special topic: Weather phenomenon:
Windstorm
We all talk about the weather but what dowe know about the wind? Where does it comefrom and what effective precautions can betaken to prevent windstorm damage to build-ings? Read about the destruction a hurricane
caused in a tourist area or what happenedwhen a container ship ran into a winter storm.We also present a chronology of devastatingwindstorm catastrophes worldwide from1970 to 2007.
More than just a mild breeze:
Wind causes more damage
than any other natural hazard
turbulent storms leave their
marks all around the globe.
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Winter Storms Daria, Lothar, and Kyrill in Europe,
Typhoon Mireille in Japan, Hurricane Andrew
and Hurricane Katrina in the United States: just
a few of the major windstorm catastrophes of
recent years that have devastated whole areas,
destroyed forests and coastal resorts, and
cost billions of euros. The frequency and dimen-
sion of the losses have had a major impact onthe insurance industry around the globe.
Windstorm is the most important natural hazard
of recent decades, in terms of the frequency of
loss events, the total expanse of the areas affected,
and, above all, the scale of the damage caused.
The insurance industry has consequently had to
carry higher and higher losses due to windstorm,
the natural hazard responsible for about 79% of
the US$ 370bn (2007 values) which the insurance
industry had to pay for major natural disasters
between 1950 and 2007 (see Fig. 1).
What do we know about the wind?
Meteorological observations of windstorm events
have been documented for centuries for almost
as long, in fact, as written history. On the other
hand, instrumental measurements of wind fields
have only existed for a relatively brief one hundred
years. Moreover, since wind fields are very sensi-
tive to the coarseness of a region topography,
vegetation, built environment it is very seldom
possible to compare them with each other over
relatively long observation periods. This is one of
the reasons why there are few areas with indicativewind statistics and windstorm hazard zoning to
date. What is more, the windstorm hazard in moun-
tainous areas may be subject to extreme small-
scale changes due to topographical features like
river valleys. However, routine meteorological
monitoring networks are usually too large-meshed
to pick up local changes in wind fields or confined
windstorm phenomena like tornadoes and thun-
dersqualls.
Special topic: Weather phenomenon: Windstorm
Windstorm The most important naturalhazard worldwide
Author
Ernst Rauch, Munich
As fast as the wind
Observations of the wind present another prob-
lem, too: the winds speed increases with its
height above the ground usually following
power law. However, it also reacts strongly to
the coarseness of the earths surface. In short,
the smoother the surface, the less the wind cur-
rent is decelerated. For this reason, wind speeds
are on average much higher over the sea than
over a surface covered with vegetation or an
urban area.
Far ahead of the rest. Historically, windstorms
have been the most important natural hazard for
the insurance industry even more than earth-
quakes, volcanic eruptions, or floods. The loss
frequency, the scale of the damage caused, and not
least the high windstorm insurance penetration
are all responsible for this.
Weather-related
events
Windstorm
Flood
Temperature
extremes
Geological
events
Earthquake, tsunami,
volcanic eruption
Fig. 1 Great natural catastrophes, 19502007:
Global distribution of insured losses
Chart: Munich Re
10%
4%
7%
79%
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Since the height at which the wind is measured
plays such a decisive role, a standard reference
height of 10 m above the ground has been agreed
on for the purposes of comparison by the World
Meteorological Organization.
Turbulent risk assessment
For an accurate assessment of the windstorm risk,
however, the insurance industry needs even more
information. One of the essential parameters for
the extent of damage is the duration of wind stress.
Many losses are only caused by a multitude of
wind attacks or load changes, which cause ma-
terial fatigue and finally failure.
Besides speed and duration, the direction of the
wind is also decisive. Severe changes in direction
can influence the extent of loss considerably, if
trees with their root system and buildings withtheir specific load design cannot cope with them.
The wind is turbulent. The wind speeds of short
gusts are much higher than the average, with the
gust factor the ratio of gust speed to mean wind
speed usually being between 1.2 and 1.5. In very
rough terrain, however, values exceeding 2 may
also be reached. The Beaufort Wind Scale defines
windstorm strength as the ten-minute mean value.
Last but not least, the turbulent nature of the wind
leads to its kinetic energy fluctuating very strongly,too. Known as the energy spectrum of the wind,
this property has a decisive impact on the extent
of damage to trees and resonating structures, par-
ticularly bridges, towers, or chimney stacks.
Windstorms from tropical to wintry
In meteorological terms, windstorms can be essen-
tially divided into four classes: tropical cyclones,
extratropical storms (winter storms), regional
storms (including monsoon storms), and local
windstorms (tornadoes, thunderstorms/hail-
storms). The world map of windstorms on pages2829 present the typical tracks and origins of
the various windstorm types.
Fig. 2 Cross-section of a tropical cyclone (hurricane)
At least 27C
3
12
4 Heavy rainShower
Diagram: Munich Re
Hurricanes get their energy from the
evaporation of warm surface water.
This schematic drawing shows how
warm air rises in the central eyewall
of the hurricane (1). This is where
the strongest condensation of water
vapour occurs, consequently pro-
ducing extreme precipitation. Out-
side the eyewall (2) and in the eye of
the storm (3) a windless, dry zone
in the centre of the hurricane the air
cools and streams back downwards.
Over the sea surface (4) it takes on
heat and moisture again providing
additional fuel for the atmospheric
thermal engine. Over land areas,
however, the system loses energy
fast when the addition of water
vapour stops and friction with the
ground sets in.
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The catastrophe potential of tropical cyclones is
exceptionally large in many coastal regions due to
the high concentration of values in such areas,
their high recreational value, and the associated
influx of people. This had a major impact on the
insurance industry again in 2005, when Hurricane
Katrina caused original insured losses of aroundUS$ 62bn.
Extratropical storm (winter storm)
Extratropical storms are different from tropical
storms not only in terms of their areas of formation
and their tracks but also, and above all, in terms of
their intensity and geographical size. They form in
the transition zone between subtropical and polar
climate zones (roughly between latitudes 35 and 70
north and south of the equator).
When outbreaks of cold polar air meet up with sub-
tropical warm air masses, extensive low-pressurevortices are generated. The storm intensity within
these vortices increases in proportion to the tem-
perature difference of the two air masses. It is high-
est in late autumn and winter, when the oceans are
already cold but the polar air is still warm hence
the designation winter storm. Their formation is
shown in Fig. 3.
Tropical cyclone
Tropical cyclones attaining hurricane force (Force 12
on the Beaufort Scale, i.e. 118 km/h) in the Atlantic
and Northeast Pacific are referred to as hurricanes;
they are called cyclones in the Indian Ocean, the sea
area around Australia, and the South Pacific, and
typhoons in the Northwest Pacific. Below hurricaneforce, i.e. in the 62117 km/h range (811 on the
Beaufort Scale), they are referred to as tropical
storms.
They can extend over large areas with wind
speeds exceeding 250 km/h and in individual cases
even 300 km/h. Coastal regions and islands
between latitudes 10 and 40 north and south of
the equator are particularly affected. The wind field
is usually 100500 km in diameter.
Tropical cyclones quickly get weaker inland, which
is primarily due to friction with the earths surfaceand the reduced energy input from water vapour.
Nevertheless, as the huge masses of water taken
up over the warm sea usually fall as rain on the
windward side of mountains, this may result in ex-
treme floods and landslides even far inland. Fig. 2
on page 20 shows how a tropical cyclone forms.
L
H
L
HH
L
H
Fig. 3 Development of an extratropical low-pressure system (winter storm)
H= High-pressure
system
L= Low-pressure
system
Cold front
Warm front
Diagram: Munich Re
L
An air mass boundary forms between
cold polar air in the north and warm
subtropical air in the south. The heav-
ier cold air starts moving southwards
close to the surface. At the same time,
the warm air advances northwards
at higher levels, with the result that
the pressure in the centre of the turbu-
lence falls. The faster cold air catches
up with the warm air, the two mix
leading to the formation of vortices.
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Maximum wind speeds are 140200 km/h,
although winter storms can also reach speeds far
in excess of 250 km/h in exposed coastal locations
and on higher mountains. Extratropical storms
may have wind fields up to 2,000 km wide.
Ice storms and snowstorms (blizzards) are furthertypes of extratropical storm. The damage caused
by ice or snow load may as in the case of the
other extratropical storms, where high wind
speeds are the main cause of damage lead to
losses amounting to tens of billions.
An ice storm lasting from 28 January to 4 February
1951 covered huge areas of the United States
from New England to Texas with a layer of ice
up to 10 cm thick. In terms of its geographical
size, it was probably the largest ice storm of the
20th century.
Regional storm and monsoon
In meteorological terms, regional and monsoon
storms are mainly classed as orographic storms.
What they have in common is that they are formed
by air masses rising on the leeward side of moun-
tains. The air cools down in the process, condenses
when humidity has passed saturation point which
sometimes results in heavy rain and rushes down
into the valleys from mountain ridges or pass sum-
mits.
In the case of regional storms, too, wind speeds
increase with the difference in temperature and
height of fall. If orographic winds additionally
combine with a large-scale stream of air moving
in the same direction, speeds of up to 200 km/h
are possible.
The best-known examples of regional storms
are the Bora on the Adriatic Coast of Dalmatia,
warm winds like the foehn in the Alps, the Mistral
in the lower Rhne Valley, and the Chinook in the
Rocky Mountains. But such orographic winds
may occur in all mountains regions of the world,
particularly on the edge of temperate climate
zones. Their formation is so closely linked to the
respective topography that it is common for them
to occur repeatedly at the same place and with
the same wind direction.
These wind systems are most intensive on theextremities of the Antarctic and Greenland, where
the extremely cold air of the central plateaus
plunges to sea level sometimes by more than
3,000 m through narrow glacier valleys. In the
process, it frequently reaches and maintains
hurricane force for long periods of time.
The monsoon is a separate windstorm phenom-
enon of regional expanse. When the great land
surface of Asia heats up under the almost vertical
rays of the sun in early and mid-summer, it draws
in warm and moist air masses from the Indian and
Pacific Oceans. Incidentally, without this circula-tion, the entire Indian subcontinent and adjacent
regions would be uninhabitable deserts.
The squall line phenomenon. Beforea thunderstorm, the air that has been
warmed by the sun becomes lighter
and rises. On its way upwards, it
cools, water vapour condenses, and
clouds form the now colder air is
heavier and finally sinks. If it falls very
fast, it forms a visible squall line. The
hanging cloud parts are the typical
manifestation of colder, moister air
sagging into the warmer, drier layer
of air beneath.
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Local storms (tornado, thunderstorm, hailstorm)
Thunderstorms are the result of vertical circulation
in the atmosphere. Cold, heavier air sinks, causing
the warm air in its path to rise. Especially when
thunderstorms form on a cold front, the air streams
down to the earths surface from a height of several
kilometres and shoots below the warm air in
tongue-form. This results in the typical squall line,
cf. photo on page 22.
As in the case of orographic storms, potential
energy is converted into kinetic energy. Gusts are
always particularly intense when a thunderstorm
is accompanied by heavy rain or hail. As a result of
the precipitation, the surrounding air also cools
down and is finally dragged down, too. Near
ground level, the stream of air veers into a horizon-
tal plane, steering raindrops or hailstones into a
sloping trajectory sometimes at an angle of more
than 45 from the vertical.
Tornadoes are small-scale storms that form in
intense thunderstorm systems when cold, dryair passes over warm, moist air masses. Given
suitable temperature differences, the cold air can
plunge downwards in a violent whirling motion
similar to the action of liquid when a bottle is
emptied quickly. On the edge of the whirling wind,
the warm air moving up replaces the cold air
moving down, condenses and thus makes the
whirling wind visible from the outside, as in
Fig. 4.
Condensation often forms at the centre of the tor-
nado, too, however. If the air pressure suddenly
falls by as much as 10% below normal, this also
leads to cooling and to droplet and cloud formation
as a result of over-saturation. The rotation of the
tornado funnel is determined, as a rule, by the
rotation of the earth, as with tropical cyclones.
Tornadoes therefore turn clockwise in the southern
hemisphere and anti-clockwise in the northern
hemisphere. However, there are also isolatedrecords of tornadoes rotating in the opposite direc-
tion.
The average width of tornado funnels is about
100 m and the average track length a few kilo-
metres, although widths of more than 1,000 m
and track lengths of up to 300 km have also been
observed. The maximum possible wind speed
on the edge of the funnel is estimated to exceed
500 km/h the highest speed of all windstorm
types. Tornadoes usually have an average wind
speed of just over 100 km/h and are most common
between latitudes 20 and 60 north and southof the equator.
As in the case of tropical cyclones, there also are
other names for tornadoes: in Japan they are called
tatsumaki and in Germany Tromben. Waterspout
is the term used when they form over water sur-
faces.
Of all wind systems, it is tornadoes
that attain the highest wind speeds.
They are generated whenever strong
vertical air movements occur in the
atmosphere and are therefore always
accompanied by intensive thunder-
storm cells. The schematic represen-tation on the left demonstrates the
air flows in and around a typical tor-
nado. Vortex formation is strength-
ened particularly by the cold, dry
air falling onto the warm, moist air
below.
Fig. 4 The formation of a local storm (tornado)
Cold, dry air
Warm, moist air
Diagram: Munich Re
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Wind is moved air. If a structure is in
its path, the wind flows around it.
Dynamic pressure is generated on
the side facing the wind, whereas
suction forces are generated on the
side facing away from the wind. On
the corners and edges of the struc-ture, vortices are generated whose
pressure or suction forces can be
many times greater. The size, fre-
quency, and intensity of these vorti-
ces depend on both the wind speed
and the shape of the structure around
which the wind is flowing. Generally
speaking, the less regular the struc-
ture, the greater the vortex formation.
Fig. 5 Encircled by the wind
Pressure
Wind
Suction
Diagram: Munich Re
Turbulence
This photo of an Oklahoma
City motel taken after a tornado
in 2003 shows how severely
the wind can damage roofs and
faades. The damage is due to
pressure and suction forces
and to vortices which form in
the air field especially on the
corners and edges of a struc-
ture cf. Fig. 5.
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The calm before the storm. Now is the time to
take precautions!
The best way to reduce windstorm damage in the
medium to long term or even to prevent it altogether
is to improve the resilience of buildings and their
components to wind. It also requires making appro-priatechanges to infrastructure installations like
bridges and means of transport (e.g. vehicle aero-
dynamics).
For the purposes of loss minimisation, all structural
components must be built to withstand the add-
itional loads generated during a storm blowing at
design wind speed. Both static and dynamic forces
must be considered, because during a windstorm
buildings are exposed to extremely volatile streams
of air that are constantly changing in strength and
direction, as Fig. 5 demonstrates.
Bad weather calls for good architecture
The influence of the wind on buildings is not one-
sided: wind flow is also influenced by the buildings
themselves. The vortices coming off the edges and
corners of a building intensify the load on it.
The resonance behaviour of the building also plays
a role. If it is an elastic structure with little damping,
strong vibrations can develop even when wind
speeds are relatively low. The constant trend
towardsmaking buildings bigger and lighter has
led to them being increasingly susceptible tovibrations.
What can be done to slow down or even halt this
loss-producing development? Here are some typ-
ical causes of damage and the corresponding loss
prevention measures:
Roofs
The roof is the part of the building that is most fre-
quently affected by windstorm damage. The rea-
sons for this are:
Wind speed increases with height. Sharp or pro-truding roof edges generate wind vortices.
Roofs, chimney stacks, roof superstructures, and
aerials, etc. are often not integrated securely into
the loadbearing structure of the building and/or
do not receive proper maintenance.
In order to avoid windstorm damage to roofs in
the long term, the following measures are recom-
mended:
When there is extensive roof cladding (e.g. corru-
gated sheet metal), screw it to the load-bearing
construction. Otherwise, fasten the individualroof elements or roofing tiles flexibly.
Anchor the roof construction in the masonry
using wall anchors, screws, and metal straps.
Simple nails are not suitable.
Building aerodynamics: Roofs that are too flat or
too steep or protrude too far should be avoided.
This will also reduce the pressure and suction
forces of the wind.
Prudent gardening: Sufficient distance will pro-
tect the building from windstorm damage causedby falling trees.
Supplies of materials: Replacement roof panels
or membranes make it possible to carry out fast
repairs and provide (at least temporary) protec-
tion against the elements.
Exterior walls, faades
Damage to the exterior walls of buildings usually
occurs only in particularly intense windstorms.
However, losses are accumulating due to the
increasing use of expensive and at the same time
sensitive wall-facing materials. Unlike conven-tional faades with masonry or plaster, these are
easy prey for the wind a really alarming develop-
ment. It makes no difference whether they involve
insulation against heat loss and moisture penetra-
tion (in the form of glued or screwed materials,
metal plates, or pressed plates) or whole faades
made of light metal or plastics.
Precautions that can be taken to prevent damage to
exterior walls and faades:
Anchor insulation and faade elements in the
loadbearing structure of the building.
Avoid soft faade materials in areas exposed to
hail.
Mount large-scale glass elements flexibly.
Ensure that the building is securely anchored in
the foundations.
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Protecting mobile facilities against bad weather
Scaffolding, cranes
Scaffolding and cranes are typical storm-prone
temporary structures, as are air domes (covers
without any supporting structure, which are keptstable by internal pressure) and tents. Strangely
enough, inadequate attention is often paid to
anchoring these structures in the ground, with the
result that scaffolding or cranes not only suffer
severe damage themselves during a storm but also
cause damage to parked cars or other buildings in
the immediate vicinity if they fall down. People
are frequently injured, too.
The following loss prevention measures are
available:
Secure the scaffolding to the buildings both
during construction and in the course of repair
work.
Replace worn, corroded, or other unsafe com-
ponents and make regular controls.
In the case of cranes that run on rails, anchor
the chassis to the rail foundation with bolts and
latches.
Unlock the jib on a tower crane to permit flexible
alignment to the wind.
A general rule regarding cranes is always to
check the bearing capacity of the ground, par-ticularly in view of the severe one-sided load
during windstorms. If necessary, they should
be secured with a cable-tensioning system.
Germany
Besides the DIN series 1055 men-
tioned below, Germany has no ob-
ligatory standards or regulationsgoverning the prevention of wind-
storm damage to buildings.
DIN 1055-4 was introduced by the
building authorities and describes
the influence of wind loads on build-
ings, their components, and exten-
sions, and regulates the calculation
methods. Additional German docu-
ments in this series like Eurocode 1
on the subject of wind load impact
may be found at
www.eurocode-online.de
VdS Schadenverhtung GmbH has
published various leaflets, some
of which are available in English.
They can be obtained for a minimal
charge at the VdS website:
www.vds.de
United States
The American Society of Civil Engin-
eers has published structural stand-
ards for protection against naturalhazards, ASCE Standard No. 7-05,
in Minimum Design Loads for Build-
ings and Other Structures.
www.asce.org
Quite a number of supplements
have been incorporated in the Florida
Building Code in response to the
devastating hurricane seasons of
recent years, in which Florida was
particularly affected.
www.floridabuilding.org
The American Association for
Wind Engineerings website offers
a number of publications on the
subject of wind and windproof con-
struction. These include not only
structural guidelines and standards
but also publications dealing with
wind energy and hurricane risk
assessment.
www.aawe.org
Worldwide
The Journal of Wind Engineering
and Industrial Aerodynamics pub-
lished monthly by the InternationalAssociation for Wind Engineering
is written for architects, civil engi-
neers, and meteorologists through-
out the world. The ISSN number
is 0167-6105.
Storm-proof construction
Further information and regulations
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The graph of expected losses as
a function of occurrence probability
or return period clearly shows that
hurricanes represent the most ex-
pensive windstorm hazard in the
United States. This is due, on the onehand, to the very high wind speed
they can attain over large areas and,
on the other, to the concentration
of values in US coastal regions like
those along the Gulf Coast or on
the southeast coast (e.g. Florida).
These two factors are not encoun-
tered in this combination either
in Japan or in Europe.
Motor vehicles, caravans
The insurance industry is always hit by extensive
losses in the motor own damage sector when there
is a major windstorm event. In regions with a high
property insurance density, the sum total of motor
own damage losses frequently amounts to 510%
of the total insured loss. This rate may also be con-siderably higher in emerging markets. Losses are
primarily the result of falling trees or branches,
roof panels, or faade components.
Possible prevention measures:
Put vehicles in the garage when there are storms
or severe weather warnings.
When there is a danger of heavy storm gusts,
close particularly exposed road sections and
bridges to large lorries and caravans.
At camp sites, secure caravans with cables.
In hail-prone areas, protect car depots with hail
nets.
A general rule is to repair damage quickly in
order to avoid corrosion and other consequential
damage.
Windstorm losses can be reduced considerably or
even prevented by precautionary measures. The
most effective way to prevent losses, however, is
to incorporate the factor of wind resistance in the
planning of infrastructure installations and all
buildings and their individual components. Land-
use restrictions in heavily exposed areas like those
on the coast are also of special significance.
Stormy days ahead
There is no doubt that losses from windstorm
events are going to increase worldwide, both from
hurricanes in the United States and from winter
storms in Europe. Fig. 6 provides a striking indica-
tion of expected losses as a function of their occur-
rence probability. How does this increase come
about? It is due to the increasing concentration of
values and also to the changes in weather patterns
as a result of global atmospheric warming. There is
hardly any line of insurance that has such a high
loss potential (in terms of single loss events) as
windstorm insurance.
Since the attitudes of the public, industry, and the
authorities are significantly influenced by insur-
ance terms and conditions, one of the insurance
industrys tasks is to advocate more effective pro-
tection. What measures are suitable in individual
cases? What prices must be charged and what
terms and conditions are needed to cover the risk
adequately? These are all questions that need to be
answered.
The suitable time to prepare for a changing risk
situation is the period of calm before the storm,
because when the storms have already begun,it is too late, as past events have so frequently
demonstrated.
Hurricane USA Windstorm Europe Typhon Japan
US$ bn
300
250
200
150
100
50
100 200 300 400 500 600 700 800 900 1,000
Years (return period)
Fig. 6 Windstorms worldwide: Expected losses as a function
of their occurrence probability
Source: Munich Re
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World map of windstorms: from tropical to wintry
Tropical cyclone (hurricane, typhoon, cyclone)
Saffir-Simpson Hurricane Scale
m/s32.742.6
42.749.5
49.658.5
58.669.4
69.5
km/h118153
154177
178209
210249
250
mph7395
96110
111130
131155
156
Knots6482
8396
97113
114134
135
Force1
2
3
4
5
Australian Tropical Cyclone Severity Scale
m/s
25.034.5
34.647.0
47.162.362.477.6
77.7
km/h
90124
125169
170224225279
280
mph
5677
78105
106139140173
174
Knots
4767
6891
92121122150
151
Force
1
2
34
5
Extratropical storm (winter storm)
Beaufort scale
m/s00.2
0.31.5
1.63.3
3.45.4
5.57.9
8.010.7
10.813.8
13.917.1
17.220.7
20.824.4
24.528.4
28.532.6
32.7
km/h01
15
611
1219
2028
2938
3949
5061
6274
7588
89102
103117
118
mph01
13
47
812
1318
1924
2531
3238
3946
4754
5563
6472
73
Knots01
13
46
710
1115
1621
2227
2833
3440
4147
4855
5663
64
Force0
1
2
3
4
5
6
7
8
9
10
11
12
40N
0
40S
Local storm(tornado)
Extratropicalstorm(winter storm)
Extratropical storm (main tracks)
Tropical storm (main tracks)
Tornadoes (main areas of occurrence)
Tropicalcyclone(hurricane)
Extratropicalstorm(winter storm)
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0 km/h 100 km/h 200 km/h 300 km/h 400 km/h 500 km/h
Local storm (tornado)
TORRO Scale
m/s1724
2532
3341
4251
5261
6272
7383
8495
96107
108120
121134
km/h6186
87115
116147
148184
185220
221259
260299
300342
343385
386432
433482
mph3954
5572
7392
93114
115136
137160
161186
187212
213240
241269
270299
Knots3347
4863
6480
81100
101119
120140
141162
163185
186208
209233
234260
Force0
1
2
3
4
5
6
7
8
9
10
m/s17.832.4
32.550.2
50.370.3
70.492.2
92.3116.3
116.4142.3
142.4169.4
km/h64116
117180
181253
254332
333418
419512
513610
mph4072
73112
113157
158206
207260
261318
319379
Knots3563
6497
98136
137179
180226
227276
277329
Force0
1
2
3
4
5
6
Typical tracks of the various storm types
Tropical cyclones usually develop in the tropical and
sub-tropical Atlantic or Pacific and then make landfall.
Winter storms, on the other hand, move as low-pressurevortices in the transition zone between cold polar air
and subtropical warm air masses. Tornadoes are devas-
tating small-scale storms, measuring between a few
dozen and several hundred metres in diameter. Individ-
ual scales are needed in order to classify the various
windstorm types because of the different wind speeds.
Significant historical windstorm events
Tropical cyclones
1970: Cyclone/storm surge, Bangladesh
1974: Cyclone Tracy, Australia
1983: Hurricane Alicia, USA
1991: Cyclone/storm surge, Bangladesh1991: Typhoon Mireille, Japan
1992: Hurricane Andrew, USA
1998: Cyclone 03A, India
1998: Hurricane Mitch, Middle America
2005: Hurricane Katrina, USA
Extratropical storms (winter storms)
1976: Winter Storm Capella, Europe
1990: Winter Storms Daria, Vivian, and Wiebke, Europe
1999: Winter Storms Anatol, Martin, and Lothar, Europe
2007: Winter Storm Kyrill, Europe
Local storms (tornadoes, thunderstorms/hailstorms)
1984: Hailstorm, Germany
2003: Tornado outbreak, USA
40N
0
40S
Tropical cyclone(typhoon)
Tropical cyclone(cyclone)
Diagram: Munich Re
Fujita Tornado Scale
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Chronology of the most devastating stormsfrom 1970 to 2007(all loss amounts in original values)
Tropical cyclones
1991 Cyclone and storm surge,
Bangladesh
A good 20 years after the 1970 catas-
trophe, Bangladesh is again hit by a
severe storm. Almost 10% of the popu-
lation are made homeless in April 1991
by a cyclone with wind speeds reach-
ing 250 km/h.
1991 Typhoon Mireille, Japan
Massive damage to buildings and crops
are caused by Mireille as it crosses
Japan in September 1991. Generating
insured losses of US$ 7bn, it is the
costliest windstorm for the insurance
industry in the history of Japan.
1992 Hurricane Andrew, United States
At US$ 17bn, the largest insured loss
until then worldwide. Also the last loss
event for a number of primary insurance
companies: Hurricane Andrew forces
them into liquidation.
1998 Cyclone 03A, India
One of the strongest cyclones to hit India
in 25 years, 03A causes losses costing
US$ 1.7bn in June 1998 and is also
Indias most expensive storm of all time.
This high sum was due to the manyindustrial facilities that were hit: refiner-
ies, tanks, ports, and wind farms.
1998 Hurricane Mitch, Middle America
In October/November 1998, Mitch is
the tragic climax of an exceedingly
active hurricane season in the Atlantic.
The death toll is the highest for over
200 years: 9,700 people in MiddleAmerica lose their lives. Honduras and