View Full Version : Smaller seat pitch leads to faster evacuation?

27th May 2002, 15:24
More fat on the fire in the arguments about seat pitch...:confused:

[QUOTE]Mon 27 May 2002

Evacuations take less time with smaller seat pitches
A study by Cranfield University has shown that ‘narrower seat pitches appear to lead to faster evacuations’ in the event of an aircraft accident.
The Times reports that a series of evacuation tests undertaken by the University, the world’s leading authority in the field, found that passengers in rows with seat pitch of 36 inches – typically the most generous available in long-haul economy class – took seven seconds longer to evacuate an aircraft than those in more cramped seating.
The conclusion drawn by researchers was that while extra space allowed volunteers to leave their seats more quickly, this caused ‘severe bottlenecks’ as many headed for the exits at the same time. Tighter seat pitches resulted in faster evacuations as they allowed a steady flow of passengers through the exits.
International regulations state that all commercial airliners must be capable of being evacuated within 90 seconds using only half the available emergency exits, while the Civil Aviation Authority, regulator of UK-registered aircraft, stipulates that minimum seat pitch must be no less than 26 inches.
The results of the Cranfield study contradict research commissioned by the CAA last year, which proposed that the minimum seat pitch should be increased by at least 3 inches.[QUOTE]

27th May 2002, 18:11
...which should lead us to the conclusion not to decrease seat pitch but increase aisle width and possibly number of emergency exits.
Now who is going to do that????

27th May 2002, 18:53
...alternatively, only thinner PAX can fit into economy seating, so exit density (ie PAX per square metre) can be higher than for the lard @rses at the front...

27th May 2002, 18:54

Wonder if Cranfield have had any unusual donations lately.

Or perhaps someone has offered to sponser a new 'chair' ;)

Kaptin M
27th May 2002, 20:50
In that case, RESPONSIBLE airline managers who put SAFETY ahead of PROFIT, should be calling for ALL-ECONOMY class configuration of their airline's aircraft.

No First nor Business Class (high yield)!!

Yeah, right!

27th May 2002, 21:02
Actually, to be serious for a moment it is not entirely impossible that there may be something to this. I remember reading an article in Nature on crowd flow some time ago. Found the link again...

Don't panic (http://www.nature.com/nature/fow/000928.html)

Anyway, one of the main findings was that our intuitions about what helps a crowd move quickly may not necessarily be accurate since people don't flow like a homogenous fluid. Perhaps most relevant to aircraft evacuations is the 'faster-is-slower' phenomenon - that is the tendency for people in a rush to end up going slower.

28th May 2002, 12:30
Cranfield's information was recently presented at a cabin safety conference...having read through the data, I must admit that I'm sceptical. The difference in evacuation times is not particularly great (4.5 seconds for the first 30 people). In fact, in at least one of the trials the 36-inch pitch evac time was three seconds faster than the average 29-inch pitch evac time.

Although the time difference between the seat-pitches tested is considered "statistically significant", that's just a mathematical definition. Given a real-life crisis and the various factors which such a crisis would throw up, I can't see that anyone would seriously believe that narrowing the seat pitch would help anyone.

28th May 2002, 12:44
How convenient for Cranfield University to release this information now!

"Welcome aboard folks. Be assured that the extreme discomfort you are about to endure for the next eight hours or so is purely in the interest of your safety........".

28th May 2002, 13:08
Konkordski wrote...
I can't see that anyone would seriously believe that narrowing the seat pitch would help anyone. Well, I don't know any of the specifics regarding the recent Cranfield study but as I wrote earlier - it doesn't seem entirely impossible that smaller seat pitches could speed evacuation.

If there is a finite rate at which people can move down the aisles and out of the exits before they start to pile on top of each other and cause blockages then restricting flow into the aisles could conceivably help.

It all depends on which part of the exit route is the rate limiting step. It seems very likely that if there is a maximum rate at which people can pile out of an exit - if there are in fact no limits on how fast people can get to and congregate at the exits then blockages could easily develop.

Imagine a cabin with no seats at all, and then think what would happen during an evacuation - everyone would rush to and crowd around the exit doors most likely slowing the rate at which people actually leave. A bit like what's going on at the door on the left here...


Or as illustrated in the figure on the top left here...


So in a normal cabin - the manner in which the aisles limit the flow towards the exits may, perhaps counter-intuitively, actually speed the evacuation rate.

Now, as I said I don't know the details of the Cranfield study but I don't think we should be dismissing it out of hand. Of course any small benefits in terms of evacuation rate would need to be weighed against the other risks associated with cramped seating.

Also it is important to bear in mind that while narrower seat pitches may speed the evacuation rate slightly - if they are used to pack in more people then they will also increase the number of people who need to be evacuated. Consequently, the net effect on the ability of a cabin to meet the 90 second rule may be zero. Unless of course, you narrow the seat pitch without increasing the number of seats - perhaps leaving large empty spaces for stretching and other activities (putting practice? Twister? dancing?)

28th May 2002, 14:04
Just to clarify, I don't mean to dismiss the idea out-of-hand. I just think that there's a big difference between "statistically significant" and "genuinely useful".

Maybe 30 people would get out of an aircraft four seconds quicker....the question is, does that justify the cost to airlines?

IMHO the hypothesis hasn't even been proven. Only three or four evac trials were performed in each case...that's nowhere near enough to start drawing conclusions on statistical significance.

The other thing which the news report above doesn't mention is the number of trials which had to be aborted because the passengers were concerned over their own safety in the crush to get out.

28th May 2002, 14:51

I'm not convinced yet either - just keeping an open mind. But I'm fairly skeptical - especially since what use is getting 30 people out 4 seconds quicker if the narrower seat pitch has been used to pack in extra seats which you'll need those 4 seconds and more to empty!!!!

For example, a quick look at some seating plans reveals that Air Canada have 260 Y seats aft of the second set of doors on an A330 - while Air Transat have 290. Presumably, Air Transat would need to be able to evacuate people approximately 12% faster than Air Canada do in order to get everyone out in the same time. Just as well they've got those tight seat pitches!!!

28th May 2002, 19:49
These studies are indeed serious. This sort of thing has been used for architecture and road traffic planning for several years, including planning major sports stadiums and concert halls. The key were advances in maths (around complexity theory I think) and computer power - I believe the first researchers were very surprised by their results and even more so when experiments with real crowds supported their findings. (One of the first was a study on traffic jams and speed limits, I think - it turned out that given whatever variables, there was an optimum speed for the highest traffic flow, and speeders held everyone else up.)

29th May 2002, 10:53
Stagger, in the case of Air Canada vs. Air Transat, the latter have 'Type A' exits at the Door 3 position on their A330-300s. This allows a higher rate of exit than the 'Type 1' emergency exits in the same position used on Air Canada's 330-300s.

Consequently, the aircraft is licensed for a higher passenger number in the rear cabin. The same licensing arrangements forced Airbus to add an overwing exit to the A340-600, as 4 Type A doors was not thought sufficient in an aircraft of that size.

29th May 2002, 11:55

Thanks for explaining that!

Here's a thought though...

If narrow seat pitches speed evacuation by restricting flow into the aisles, thus preventing crowding and blockages at the doors. Then, if the doors are bigger you should be able to achieve a higher rate of flow towards them before you start to see blockages and the “faster is slower” phenomenon coming into play.

Consequently, with larger exits the benefits of narrower seat pitches may not manifest themselves. In, fact they could restrict the flow to below the optimum rate – i.e. the maximum throughput of the door.

29th May 2002, 19:13
May I draw your attention to the British Airtours accident in Manchester in 1985.
It was found that major contributing factors to 55 lives being lost were narrow seat pitch and limited access to the emergency exits.
As far as I recall (but I am not too sure about that) extensive evacuation tests carried out afterwards proved that had access to the emergency exits been only a few inches broader this would have speeded up evacuation tremendously because of a well-functioning evacuation flow.

From the official accident report:
The narrow gap of 10¤ inches available between row 9 and 10 seats impeded passengers' access to the right overwing exit. The pressure of passengers on the 10F seat back caused failure of the seat back hinge baulk allowing the backrest to fold forwards creating a further obstacle to egress. Twin bulkheads in the forward cabin restricted evacuation flow to the forward exits after both were open.
The present regulatory Evacuation Certification Requirements are inadequate in their evaluation of important potential egress restrictions and make no attempt to demonstrate evacuation times in the conditions where speed of evacuation is of prime importance - that of egress in conditions of dense smoke.
The major cause of the fatalities was rapid incapacitation due to the inhalation of the dense toxic/irritant smoke atmosphere within the cabin, aggravated by evacuation delays caused by a forward right door malfunction and restricted access to the exits.

There is also a website somewhere about the tests carried out in the wake of that particular accident, but I can´t find it right now. These tests did, indeed, look deeply into the field of passenger flow under evacuation conditions (panic, smoke, etc.)


29th May 2002, 20:32

The section of the report you cite focuses on the narrow gap between seats through which people had to access the overwing exit itself - i.e. it was the limited rate of flow of people at the exit point that was the problem and contributed to the tragic outcome.

However, the seat pitch of the rows from which people enter the aisle in order to travel towards the exit is an entirely different matter. Does anyone know if this was studied in relation to the British Airtours accident?

I think the bottom line is - all exits have a maximum throughput before problems arise - and obviously the seat pitch at the exit row may be a significant limiting factor determining this rate. Consequently there may be little to be gained from people being able to travel towards the exit at a faster rate than they can get out of it.

Put it this way - if people can get into an aisle at a faster rate than they can leave that aisle then that aisle will start to fill up and people will end up on top of each other. The seat pitch at the exit row is a determinant of the exit rate and this should probably be as wide as possible. The seat pitches for other rows are determinants of the input rate and thus there could be benefits to them being narrower.

Tin Kicker
29th May 2002, 21:20
I've seen an article in recent weeks (Flight?) documenting tests with directed sound which lets pax find exits even in smoke. I think it said that its been officially sanctioned for use on ships but aviation is still sitting on the fence about it all. Typical.