Wednesday, July 28, 2010

Evacuating the Love Parade

An important issue for crowd safety is how long it would take to evacuate a venue. Like the last article this is not to attempting to figure out the exact right answer to how large entrance/exits need to be but to try see if someone with a limited knowledge and a search engine could easily see in advance that the entrance/exit to the love parade was dangerous. Even large venues can require evacuation in the case of a natural or manmade disaster. These disasters could be weather related as happened here here and here. In the case of man made safety risks venues also are sometimes evacuated. As described here
"On December 12, 2004, the stadium Santiago Bernabeu in Madrid was evacuated because of a bomb threat.... In eight minutes, more than 70,000 people left the premises without incident."

The respected Spiegel says

"Much of the critique has centered around the fact that the tunnel where the panic took place was the only entrance to and the only exit from the party site. "
If this tunnel was the only exit available (another tunnel seems to have been reserved for emergency vehicles) how quickly should people have been able to exit?

This soccer stadium with a capacity of over 25,000 claims 'The target evacuation time for the entire Stadium at full capacity is 8 minutes.'

This document on evacuation planning states
"The maximum Emergency Evacuation Time for sports ground varies between two and a half minutes and eight minutes"

Stadiums do not have as much free space as larger venues but they still allow for moving people onto the pitch as happened at a baseball game after the 1989 San Francisco earthquake. In the case of some natural disasters or terrorist threats a site wide evacuation might be needed so even large sites probably need to be able to be evacuated reasonably quickly.

The acceptable evacuation time for a stadium seems to be under ten minutes. If Spiegel is correct and this tunnel really was the only exit any evacuation would have taken hours which is not be acceptable.

The pictures here give a very good impression of what happened. The width of the tunnel does indeed look like 16 meters. And the 'ramp' described earlier just looks like something people tried to escape up rather than a designated route.

Monday, July 26, 2010

How many people can pass through a tunnel?

A tragedy happened at the love parade when 19 people lost their lives. This will be investigated by professionals who will come out with detailed analysis on how this incident took place. I want to see what someone in half an hours worth of searching can say about how wide a tunnel you need to fit that number of people.

I worked as a volunteer at the special Olympics some years ago. The job mainly involved making sure spectators could get into and out of the events easily, that emergency services can easily gain access and that spectators and athletes were kept separate. The venues were not huge and the spectators were happy and sober. Still I got some impression of the kinds of things needed to ensure crowd safety at events.

I want to put a figure on how many people could safely fit through the tunnel that was the sole access point to the love parade venue. A 16 meter width is given by most media outlets.

But some say it is 30 meters wide. Most seem to put the number of people there at 1.4 million but others at only 500,000 'an event set up for 250,000 ended up with an estimated 500,000 to 1 million'.

How long does it take to get everyone into a venue? How many people an hour will try enter a venue? I do not think all 1.4m people try enter in an hour. But I would guess most people try to enter a venue in a three hour period. Each hour you could expect over 300,000 people to try and enter through the tunnel. People are unpredictable meaning that you would need to be able to have more than this safely in case loads turn up at the same time.

Who else deals with crowd volumes like this? Every few years during the Muslim Hajj there is a crowd related accident. They are building a new bridge to improve safety. There is a description of this bridge here (pdf).
the new, multi-level bridge structure which will accommodate and ease the flow of 3 million worshippers during a single daylight period. The proposed new Jamarat bridge is a superior structure formed of 4 platform levels... each of the bridge’s 4 floors is roughly 600 m-long, with variable widths (ranging from 60 m to 97 m

The engineers describe these 4 floors as at least 60 meters wide. Each 60 meters in width is supposed to handle .75 million people if scaled linearly to 16 meters that would be 200 thousand people during the day. The new Saudi bridge is designed with a much larger channel to move people than they had in Germany. Pilgrims may act differently to other crowds as they stop to perform religious ceremonies.

Another terrible crowd incident was the Hillsborough disaster where 96 people died. A quick search about football crowd safety found this document. It is a very interesting article and well worth a read

The document states
"the safety limit for crowd density is defined as 40 people in 10 square metres for a moving crowd" the tunnel at 16m wide and 100 meters long should only hold 6400 people. Walking at 38 meters per minute. 100 meters would mean it would take 156 seconds to get through the tunnel. 6400 people every 156 seconds is 147,000 in an hour. This means it would take ten hours for 1.4 million people to safely travel through.

Reuters here states
"Authorities have not yet been able to explain how exactly the tragedy happened -- near a tunnel that led to a ramp into the festival grounds. Most of the victims were found dead on the ramp and none in the tunnel, authorities said"

The football document also in Section '2.8 Wembley Complex Station' gives this equation
No. of Units of Exit Width = Number of Persons (1)
required (each width = 0.55m) Flow Rate (2) x Evacuation Time (3)

"Where number of persons (1) means the maximum number of people that could be expected to be on a platform at any time. Flow rate (2) means 40 persons per minute for escape routes incorporating stairs, and 60 persons per minute for level escape routes (without stairs). Passenger walking speeds should be assumed to be 38 metres per minute for horizontal circulation."

Using the Wembley equation above 16 meters *.55 meters means 29 people can safely span across the tunnel. 40 flow past a minute if the escape route has a stairs and 60 if it is flat. The ramp sounds like it would hinder flow in a similar way to a stairs.

Once again this is all back of the envelope and as more facts come out a much better estimate of how many people could safely negotiate the site will emerge. A reasonable estimate of the number of people who could travel through the tunnel in an hour is (tunnel width/person width)*number or people per minute * 60 minutes
which in a 16 meter wide tunnel with a stairs at the end is (16/.55)*40*60=70,000
Best case scenario with a wider tunnel and no stairs 30 meters/.55 meters *60 people *60=200,000 which is less than the expected number of people.

This calculation indicates that a cursory look at at the venue entrance would give someone grave concerns about safety for a smaller crowd than turned up on the day.

Tuesday, July 20, 2010

Science grows 2.5% annually why doesn't the economy?

What causes economic growth? Much of the world still lives in grinding poverty, figuring out a way to get them out of this is important. The best way seems to be for their economy to grow.

There are many theories as to what causes economic growth. The founder of Google claims
"Virtually all economic growth (in the world) was due to technological progress. I think as a society we're not really paying attention to that," Page said. "Science has a real marketing problem. If all the growth in world is due to science and technology and no one pays attention to you, then you have a serious marketing problem."

If technological progress causes growth there should be a link between the amount of scientific progress and the amount of growth. Here is a very interesting article about the rate of the increase in scientific knowledge.

'What I found, using this simple proxy for difficulty, in each field — biology, astronomy, chemistry — was a curve with the same basic shape. In every case, the ease of discovery went down, and in every case it was a curve called an exponential decay ...[I] discovered asteroids get 2.5 percent smaller each year. So while the ease of discovery drops off quickly as early researchers pick the low-hanging fruit, it can continue to “decay” a long time, becoming slightly harder without ever quite becoming impossible"

Say science increases in the level of knowledge by 2.5% a year.

What is the rate of economic growth? 'Since 1820, world development has been much more dynamic. Per capita income rose more than eightfold, population more than fivefold.' 190 years growth 8 fold increase is a growth rate of about 1.1% per annum. Or for two specific countries the UK from 1830 to 2008 had average real GDP 1.97%. The US 1830 to 2009 real GDP of 3.62%.

Other things cause economic growth

-Demographics more people of working age means more stuff gets made.

-Institutions. The rule of law matters. If people think anything the build will be plundered off them they wont build much.

-Governments. Some ways of running a country seem to result in more economic growth than others. Communism was never that good at creating economic growth for example.

-Taxation. At a certain point if you tax people too much they wont work anymore. If you dont tax people enough you might not be able to afford schools. Knowledge of what level of taxation is beneficial to economic growth should improve over time.

-Financial innovation. By getting capital to the people who best use it financial innovation is supposed to help economic growth. If it doesn't we should not spend money bailing out investment banks.

-Foreign aid: Aid to developing countries seems to have a mild positive effect on their economic growth rate though in specific areas it seems to have a negative effect

What else can affect economic growth and how great an effect does it have?