Prof. Edwin Galea, director of the Fire Safety Engineering Group at the UK's University of Greenwich, argues in a current paper that the overall approach to emergency evacuation planning needs a new look.

For example, the 60-foot maximum distance from passengers to an emergency exit is wholly arbitrary. "The rule is not founded on any fundamental understanding of evacuation dynamics, accident scenarios or human behavior," Galea wrote (the A380 exit configuration satisfies the 60-ft. limit, by the way). "The rule even ignores the nature of the exits (e.g., exit size) ... at the end of the 60-foot separation."

Moreover, evacuation trials for certification purposes also are arbitrary. According to Galea:

"As volunteers are subject neither to the trauma nor to the physical ramifications of a real emergency such as smoke, fire and debris, the certification trial provides little useful information regarding the suitability of the cabin layout and design in the event of a real emergency. The Manchester disaster of 1985, in which 55 people lost their lives, serves as a tragic example. The last passenger to escape from the burning B737 aircraft emerged 5.5 minutes after the aircraft had ceased moving, while 15 years earlier in a UK certification trial, the entire load of passengers and crew evacuated the aircraft in 75 seconds."

Galea maintains that computer simulations of emergency evacuations, as embodied in the airEXODUS model that he and his colleagues have developed, might well provide a higher level of safety. By running 1,000 evacuation simulations under a variety of conditions (e.g., smoke, size and evolution of fire, passenger hesitation, various combinations of blocked exits, etc.) a more "holistic" assessment of evacuation capability of a particular aircraft design could be developed, and the design optimized accordingly.

"Under the current 'make or break' single test regime, a single performance result is selected from [an] unknown distribution of possible evacuation times and put forward as the certification performance," Galea wrote. "Rather, the industry should be endeavoring to produce a more meaningful measure of aircraft certification performance." Galea is calling for more than advanced computer simulations. Rather, he is calling for a reconsideration of preconceptions concerning certification. Timothy Snyder, a risk analyst at Connecticut's Fairfield University, shares Galea's perspective, to a point. "Computer simulations won't capture all the human interactions, such as a parent waiting at the bottom of the A380 stairway or, worse, traveling against traffic up the stairs, for their family seated topside."

"People do not behave like water flowing out the holes of a vessel, they are all independent entities," he cautioned. However, Snyder added, "Computer modeling can help determine how to best design the exits and the evacuation procedures."

Galea recognizes the limitations:

"It is not sufficient to simply replace full-scale testing of aircraft with a combination of computer modeling and component testing. While this may make testing the aircraft a safer and more efficient process, can we also make the aircraft safer by design? If we are to rise to this challenge, it is essential that we begin to question some of our current preconceptions concerning certification."

For building evacuations, Galea pointed out, the risk analysis features the concept of available safe egress time (ASET) and required safe egress time (RSET). The ASET may be based on the time for a layer of smoke to descend to head height, while the RSET may be the time for occupants to vacate the structure.

"Put simply, the ASET must be greater that the RSET," Galea said. Computer models are now being used to assess the interactions of building designs, evacuation environments, and population behaviors in various disaster scenarios.

"A similar approach should be considered for aviation," Galea maintained. >> Galea, e-mail E.R.Galea@gre.ac.uk <<