Sunday, June 27, 2010
Icelandic Volcano: How Much Ash Is Dangerous?
Figure 1 Image ash plume from the Eyjafjallajökull volcano
I hate flying. No that is not quite true: I hate the thought of crashing, of a massive heavy metal object plummeting 30-odd thousand feet to the ground with me in it. I do fly though, I have to for work and for holidays, so I may not be the person you most want to sit next to on a plane. Having just made it back from a second year field class in Malta when the Eyjafjallajökull volcano erupted ejecting ash to between 20,000 and 30,000 feet, you can imagine I watched the news with great interest.
Aside from hearing news of the second year Berlin fieldclass who had to trek across Europe to the Belgium coast to get back, my interest was caught by the debate, carried out with more than a hint of repressed anger, between the Meteorological Office, the Civil Aviation Authority, the government and airlines. The Met Office view is outlined through their press releases (http://www.metoffice.gov.uk/corporate/pressoffice/volcano.html) whilst the BBC archives provide details of the chronology and debate, at least the public aspect of it (http://search.bbc.co.uk/search?go=toolbar&uri=%2F&q=icelandic+volcano and hunt around for something of interest).
Figure 2 Map of extent of ash cloud impact. Source: Metetorlogical Office
The particular angle I was interested in, however, was how this diverse set of actors came together because of a specific geophysical event and how what was viewed as ‘safe’ changed as the travel chaos unfolded at airport across Europe. Eyjafjallajökull itself could be seen as an actor in its own right with its own spatial extent, temporal behaviour and characteristics such as size and shape of ash particles released. The other actors in the drama, the Met Office, the CAA, the government and the airlines were all entwined in a complex web of relationships that focused on the definition of what was a safe level of ash for flights.
The definition of safe level was central to everything that happened in late April and early May 2010. Having never had such a massive eruption with a set of meteorological conditions that pushed the ash plume over the major flight paths across most of Europe the organisation assigned responsibility for safety fell back on the ‘safe’ position of stating a of stating a zero tolerance level (a little ash was allowed in the standard threshold of a concentration of 200 microgrammes per cubic meter), no ash you could fly, any ash (above standard threshold) you couldn’t. Given the damage that ash plumes had caused for aircraft engines in the past this seemed a ‘safe’ position.
Figure 3 British Airways engine after a run in with a volcanic ash plume in 1982. Image: Eric Moody, British Airways
But how did the CAA know this. Advice is provided by VAAC (Volcanic Ash Advisory Centres – see http://www.ucl.ac.uk/news/news-articles/1004/10041901 for an outline of the global warning system and its history). But how do they know? There may have been 80 incidents since 1982 but the Icelandic eruption was something different because of the geophysical conditions, a continuous stream of ash and meteorological conditions that meant it affected European airspace. The other actors in the network, once the duration of the hazard became clearer, did not passively sit there and accept the CAA advice and the Met Office evidence. BA, for example, undertook a ‘test’ flight through the ash cloud and, emerging safely the other side, declared they felt there was no danger. Likewise, as travel chaos grew, the airlines questioned the evidence upon which the advice was based. The focus of their attention was the use of modelling rather than monitoring to predict ash cloud movement. Despite using such modelling techniques to predict weather patterns that airline use, the ash cloud models were heavily criticised for not matching the reality the uninstrumented ‘test’ flights of the airlines showed.
The definition of ‘safe’, a fixed thing you might think, became a subject of negotiation within the network based on the interest of each of the actors. The details of the zoning of the ash cloud can be found at http://www.metoffice.gov.uk/corporate/pressoffice/2010/volcano/forecasts.html. Black zones have 20 times the standard threshold ash concentration (concentrations of over 4,000 microgrammes per cubic metre), grey zones have concentrations between 10 and 20 times the standard threshold (concentrations of 2,000-4,000 microgrammes per cubic metre). The standard threshold of concentrations of 200 microgrammes per cubic metre was used to define the edge of red zones. Each zone had associated with a it an additional definition – red zones stated the concentration was as used in official VAAC products. To operate in grey zones airlines had to present the CAA with a safety case that included the agreement of their aircraft and engine manufacturers. Black zone were stated to be zones where the required tolerances of engine manufacturers were exceeded.
So is ‘safe’ a fixed term, something that is unaltered by circumstances, by context? The above summary would suggest not. ‘Safe’ levels of ash became a term that could be defined, redefined and negotiated between the actors. Scientific evidence, which you may think could decide the issue, was itself open to debate and discussion. In my next blog about the ash cloud I will look at this negotiation of evidence in more detail