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Extreme Value Analysis: its potential use in crowd safety planning
Edited version of a BNU workshop paper
Delivered January 2011
Mick Upton
Abstract
This paper considers Extreme Value Analysis methodology as a first step in the
process of assessing risk when planning for crowd safety at organised social
events. The origins of a two level system of analysis are discussed and the way
that the system can be adapted for crowd safety planning use is explained. The
paper then moves on to provide practical examples of how the system can
improve crowd management planning. .
A scientific explanation
Extreme Value Analysis (EVA) is simply a method of estimating the probability of
a rare event. It is perhaps best known for its application in meteorology where it
is used to predict the likelihood of extreme weather conditions such as heavy rain
maximum frost penetration or extreme wind conditions. The method is also used
in engineering to predict the possible failure rate of a mechanical system. A wider
application to crowd safety planning was used by Brian Toft (1990) in his thesis,
A failure of hindsight, to support his argument that crowd related accidents
should not be treated as unavoidable acts of god but more likely a failure of risk
analysis.
Toft explained that the EVA method requires the crowd manager to conduct a
program of research on two levels in order to complete a comprehensive risk
analysis prior to documenting a risk assessment for his/her future event. This two
level study of previous crowd related accidents was explained by the researcher
to be:
 A Low frequency - High intensity accident or incident. Explained as being a
crowd-related accident that occurs rarely but when it does happen it results in
a high casualty rate
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 A High frequency - Low intensity accident or incident. Explained as being a
crowd-related incident that might occur at regular intervals but result in a low
casualty rate.
In support of his thesis argument Toft provided two examples of fires at
entertainment venues that were the cause of loss of life. The two fires occurred
at the Iroquois Theatre, Chicago, 1903, and the Coconut Grove Nightclub,
Boston in 1942. Both fires appear to have occurred in remarkably similar
circumstances.
Toft explains that in both cases the decorative fabric of the interiors was highly
inflammable, exits were locked or had not been provided, both venues were
overcrowded and neither establishment had trained their staff to deal with an
emergency such as fire.
It would be a dangerous assumption to dismiss Toft`s comparative study as
being simply two fires that occurred coincidentally in similar circumstances
almost forty years apart. He simply chose one example to illustrate a low
frequency – high intensity incident. The rationale applied by Toft was that had the
operators of the Coconut Grove nightclub researched the cause and effect of
fires at entertainment venues they would have found the basis for improved
crowd safety planning at the Coconut Grove nightclub years later.
The time period between the two fires is irrelevant. For as the philosopher
George Santayana (1905) famously warned, “Those who cannot remember the
past are condemned to repeat it”. Sadly it would appear from the evidence
available today that the contributory factors to a high loss of life in the two fires
cited by Toft still appear to be contributing factors to a high loss of life in fires at
clubs and discos today.
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Fires at indoor venues are obviously not the only cause of loss of life at
organised crowd gatherings. There have been fatal accidents due to high density
crush situations, cultural behavior and falls at crowd gatherings that range from
concerts to religious meetings and retail outlets (shops). Wherever crowds are
encouraged to form the possibility of an accident exists and it might be argued
that the larger the crowd the greater the potential for an accident simply because
more people increase the likelihood of an incident. This does not imply that all
organized crowd gatherings are dangerous, rather that it is essential to plan for
the needs of a crowd.
The event organiser has a mandatory obligation to ensure maximum safety
standards for the public attending their event and common practice in the UK is
to delegate responsibility for crowd safety to a crowd management consultant.
The delegation of responsibility to a consultant does not mean that the event
organiser is absolved from all responsibility however because their choice of
consultant would be a prime consideration at an inquiry into an accident. On that
basis it is reasoned here that it is good practice for all individuals and
organisations involved with crowd safety planning to have an understanding of
the two level approach to risk analysis that the EVA method recommends in
order to make an informed choice of consultant.
Low frequency – High intensity
An obvious start point for a better understanding of the EVA method is low
frequency – high intensity. Simply because a high intensity indicates a fatal
accident and therefore information regarding the possible cause and effect are
likely to be available from press accounts, online reports and public inquiry
reports.
Great care needs to be taken when considering statements made by members of
the crowd however. Regardless of how tall a person is, when they are standing
within a dense crowd they cannot see what is taking place even when an incident
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is unfolding close by. People in a crowd situation tend to make uninformed
comments to the media. This is a particular problem with accidents at concert
events where fans rarely consider the artiste on stage to have contributed to the
cause of an accident, even if the artiste has encouraged reckless or irresponsible
behaviour. Fans are far more likely to accuse a front of stage pit team of failure to
act or the promoter for failing to take action to stop the show. The crowd
manager therefore has to critically appraise the information obtained on crowdrelated accidents and a reasonably accurate cause and effect pattern
documented for possible reference later when planning an event.
An example of the value of data collection and storage can be seen if we turn the
clock back to 1989. Imagine that we are responsible for planning for crowd safety
at an important FA Cup football match at Hillsborough between Nottingham
Forest and Liverpool. Online research would not be easy in 1989 but crowd
safety issues have been documented since the first FA Cup Final at Wembley
Stadium in 1926 when literally thousands of people without tickets climbed over
the stadium walls. Information is available if we look hard enough.
If we had studied the documented history of accidents and incidents at football
grounds we would easily have discovered that thirty-three people died and an
estimated five hundred others were injured during a FA Cup match between
Bolton Wanderers and Stoke City on the 9th March 1946 at Burnden Park, Bolton.
The Molwyne Hughes Report into the Burnden Park disaster indicates that
possible contributing factors to the loss of life in the accident were:
 Late arrival of a large crowd
 Game started while a large number of fans were still outside trying to get into
the ground
 Failure of crowd control outside of the ground
 Ingress system at one section of the ground unable to cope with a crowd rush
 This resulted in high crowd density in one section of the ground
 A perimeter fence prevented people in distress form moving onto the pitch
 The police assumed that they were dealing with a public order problem
 Venue staff were untrained volunteers
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

A perimeter fence then collapsed causing injury
A police officer had to go onto the pitch to ask the referee to stop the game
once it was realised that there was a serious safety problem
 Crowd members in other parts of the ground then assumed that the police
had stopped the game because of disorder by a section of the crowd
Now fast forward forty-three years to our match at Hillsborough and our pre
match planning has focused on the need to maintain public order because soccer
hooliganism has been an on going problem for years now. On mach day our
crowd segregation plan is working well and the match starts on time. Then a
large crowd arrives late to one section of the ground where the ingress system
cannot cope. The police cannot control the crowd outside and hundreds of
people rush into a pen that is already full. We have not trained our stewards to
deal with the situation and the police immediately assume that they are dealing
with a public order problem. Sadly ninety-six people die and hundreds more are
injured as a result of being trapped behind a pitch perimeter fence.
Given the fact that our 1989 disaster has occurred in remarkably similar
circumstances to that which occurred at Burnden Park forty-three years earlier,
what does that say about our approach to match day planning?
High frequency – Low intensity
Turning to high frequency – low intensity assessment, possibly the best example
can be seen regularly at pop and rock concerts where many hysterical or
distressed members of an audience are extracted from the crowd at the front of
the stage and taken to first aid. Experienced practitioners will know that it is often
the case that literally hundreds of young people will be treated on site and then
allowed back into the audience to continue watching the show. Responsible
concert promoters put front of stage barrier systems into place to deal with these
situations and they continually upgrade these systems to cope with new cultural
attitudes. Consequently the press rarely reports such incidents.
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This does not imply that information cannot be found; rather that it takes more
effort. Take for example a casual BBC TV News (2008) report that a crowd of
2000 mainly young women turned up to see a free concert at Fairfields Hall,
Croydon, on the 30th October 2008 by the UK group JLS. The venue only holds
1500 people and not surprisingly there were reports of crowd hysteria from young
women that could not get in. This report does not however seem to have flagged
up a warning for the management of a shopping centre in Manchester because in
2009 the Daily Mail (2009) reported that “Thousands of screaming fans turned
out to see the group JLS as they turned on the Christmas lights at the Trafford
Centre”. The paper further stated that “The gates were firmly closed by 4pm, as
the giant shopping centre was almost overwhelmed”.
On the 14th November 2009 local authority organisers of a free concert by JLS in
Birmingham were surprised when a larger than expected crowd of young females
turned up to see a free concert. The venue was full, but people appear to have
broken through a barrier system and the concert was cancelled for public safety
reasons. In each of the incidents cited here the event was free, more people
arrived than the organisers expected, the crowd profile was predominantly young
female and crowd hysteria was a key factor. Fortunately there were no serious
injuries recorded and therefore might be regarded by safety planners as being
three `near miss` incidents. It also raises the possibility that at least two previous
warnings were overlooked by the organisers of the Birmingham event.
Similarly, the organisers of an appearance by the boy band One Direction in
Wolverhampton on the 8th December 2010 seem to have been taken by surprise
by the actions of the crowd attending the open air event. A press report claimed
that 35 young female fans required medical treatment at the free promotional
concert (Daily Mail 2010). It appears that fans turned up very early to the free
event, possibly not having eaten and waited for a long period in temperatures
below zero. This scenario is remarkably similar to that of the 1979 Cincinnati
disaster referred to at the beginning of this paper that cost the lives of eleven
young rock fans.
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It is not always as easy to predict a potential incident, but the cause and effect of
so-called near miss incidents that occur are crucial to a risk analysis process. For
as Toft (1990b) quite rightly argued, “near misses should not be shrugged off but
instead be treated as fortunately benign experiences, since if the same events
were to repeat themselves in less forgiving circumstances then disaster might
ensue”.
Cross organisational learning
Where there is a lack of credible data on accidents at a particular category of
event the researcher must extend their area of search beyond their particular
event or venue in order to take into account the importance of what is often
referred today as environmental psychology. In his discussion on the concept of
isomorphism (the similarity of organisms of different ancestry), Beishon (1980)
argued that:
`It did not matter whether a particular system was
biological, sociological or mechanical in origin, it could
display the same (or essentially similar) properties, if it was
in fact the same basic kind of system`.
Consequently, even when two systems might appear to be completely different, if
they posses the same or similar component parts or procedures then they will
both be open to a common mode of failure. It can be assumed from this that a
queue system requires the same level of attention regardless of what people are
queuing for. For if seemingly different systems can display the same or similar
properties it follows that they can also be subject to the same failure modes. Toft
drew on this hypothesis to argue that the similar features of accidents were that
any failure that occurs in one system would have a propensity to recur in another
`like` system for similar reasons.
Concert planners for example can learn lessons from queue systems failures at
special offer sales at retail outlets. The common factor is that pre event
marketing shapes the psychology of the crowd prior to their arrival. At concert
events crowds will arrive early regardless of the fact that they have a ticket
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because they are determined to get as close to the front of stage as possible
while at sales people arrive early to obtain a bargain. In this scenario specific
attention needs to be paid to queue and ingress management, staff training and
communications
Some retail managers appear to have been slow to take advantage of inter
organisational and cross organisational learning. Reports indicate that there has
been a number of `near miss` incidents at retail outlets. Stores that have failed to
learn include: IKEA, (one serious incident in London and a fatal incident in
Jeddah); Primark (two serious incidents in London); Gucci’s flagship store in
Knightsbridge, West London (public disorder during queuing) and Curry’s
store Birmingham (one serious incident). In each case it was reported that
thousands more people turned up than was expected and staff were not able to
control queuing and ingress and the police were called to restore public order.
Far more serious was a queue failure at a Wal-Mart store in America where one
person died. From TV and press reports on these incidents it would appear that
store managers and staff in all cases did not have the knowledge and training to
understand crowd behaviour therefore they failed to understand the powerful
forces that can be generated by crowds in spite of the fact that there were
numerous warnings.
Conclusions
At the key stage of event risk analysis there is much to be gained by conducting
a wide-ranging program of research into crowd related accidents and incidents. It
is a fatal mistake to restrict the search to your own particular event or venue type.
For example, football Safety Officers should not focus solely on football incidents
or sports grounds, equally the concert promoter should not ignore incidents that
appear to have nothing to do with concert events. Crowd safety risk analysis
needs to focus on the possible environmental psychology of crowds during four
key phases of;
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



Crowd arrival and queuing
Ingress and/or processing
Attendance
Egress to include possible evacuation
The overall aim throughout each of these phases is to control crowd density. The
nature of the event or venue type is irrelevant as even the best architecturally
designed venues can experience an accident if arrangements are not made to
take into account the attitude of an attending crowd.
Ref used
BBC TV 2008: BBC Television News report: Hysteria at Croydon
Theatre 9th December 2008
Beishon 1980: The concept of isomorphism: quoted by Toft B. 1990
in A failure of hindsight: Published thesis
Daily Mail 2009: Its JLS mania as thousands of fans turn out to see X
Factor group turn on lights: 5th November 2009
Daily Mail 2010: Girls go wild for One Direction: Page 3 Thursday
December 9th 2010
Santayana G.1905: The Life of Reason, Volume 1: BiblioBazaar 2009
Toft B.1990: Thesis: A failure of hindsight: University of Exeter 1990