26 September 2005
26 September 2005
Concerns on the health hazards caused by carbon fibre materials following aircraft crashes were highlighted at the recent Composites in Fire conference in the UK.
John Andrews from Post Crash Management Systems has called on the composites industry to adopt a more proactive stance in addressing the post crash hazards of carbon fibre composites - not only in aircrafts, but more generally – following luckliy unrealised suspicions that were first aroused shortly after the Airbus A340 crash in Toronto in August this year.
Andrews points out that for some 15 years people in the aircraft crash response business have been concerned about the possible health hazards caused by composite materials - particularly carbon fibre composites - at aircraft crash sites.
The Airbus A340 aircraft which crashed on landing at Toronto airport on 2nd August 2005 is one of the largest aircraft currently in service which has structures incorporating a high percentage (Approx 22% or 28 tons) of composite materials - mostly carbon fibre.
The issue was first raised when, in 1990 a RAF Harrier GR5 aircraft crashed and personnel suffered health hazard problems and casualties at the crash sites. The structure of this particular aircraft was approximately 30% carbon fibre composites which represented about 0.6 tons – far less than the amount of carbon used on future aircraft such as the A380 and 787 which contain 58 and 75 tons respectively.
Andrews points out that many of the health problems experienced in the 1990 crash were due to the release of respirable carbon fibres during the crash.
Research at Farnborough in the 1990's indicated that if carbon fibre composite material is shattered in the absence of fire there will be little or no release of respirable fibres. If you burn carbon fibre composite material without subjecting it to high energy impact there will be little or no release of respirable fibres. However, if you subject carbon fibre composite material to high energy impact while simultaneously burning it with a high temperature flame - typically 1000ºC (typical aircraft crash conditions) significant quantities of respirable fibres may be released.
The fibres, depending on the type of carbon fibre, are typically 2-3 microns in diameter and perhaps 15 microns in length. They are non-toxic but have a strong affinity to dirt, and, as they easily penetrate human skin and tissue, they carry the often highly toxic dirt of the crash site into the unprotected skin of anyone working at or visiting the crash site. The results on the first RAF Harrier crash sites in 1990 were traumatic dermatitis on exposed skin coupled with a few cases of discomfort in breathing.
“Once the problem was understood it was not difficult to introduce effective personal protective measures and site clean-up procedures, and I must stress that carbon fibre composite materials were only one of a number of hazardous materials which had to be dealt with appropriately at the site of an aircraft crash We continued to deal with the occasional crash of our relatively small composite aircraft carefully and safely but we watched the steady increase in the use of carbon fibre composites in ever larger aircraft with a little apprehension”, Andrews said.
In the case with the Airbus crash earlier this year at Toronto, the aircraft failed to stop on the runway and smashed through a fence coming to rest close to a small river. All the crew were evacuated and passengers escaped with only relatively minor injuries.
Andrews said that during the escape, a major fire had started under the plane, which the Airport Fire Department reacted promptly to. Unburned fuel collected under the aircraft and reignited several times, assisted by the occasional exploding oxygen bottle, before finally being extinguished.
At the crash site there was plenty of shattered composite material which required careful handling. There were also large quantities of burned carbon fibre particularly from the tail section and the control surfaces, but luckily there was no evidence of respirable carbon fibres. The key factor being that the aircraft had stopped moving before the fire commenced. The weather was mainly hot and dry and one of the main health hazards at the crash site was the respirable dust and ash which contained the products of combustion of the aircraft. The occasional short sharp shower of rain helped to reduce the dust problem but the use of respirators was essential for all those working at the crash site. Some of the fragments of burned carbon fibre had been carried by the wind some 100 -200m outside the established cordon area and was a topic of concern to those planning the eventual clean up and restoration of the site which involved the removal of over 200 tons of contaminated earth, ash and debris.
Andrews suggests that the crash conditions with the A340 at Toronto were abnormal. Far more typical in an aircraft crash are the simultaneous conditions of high energy impact and fire which would result in the release of respirable fibres. Future trends in the design of passenger aircraft, and the increasing use of carbon fibre composites, mean that the release of respirable fibres at future crash sites - with the consequential increased health hazard, is almost inevitable.
With the problem not confined to aircraft, the risk of high energy impact combined with fire in future road and rail vehicles using carbon fibre composites is only too apparent. Andrews suggest that the answer to this problem is increased hazard awareness, and the consequential training of the emergency services and all those who need to work on or visit a crash site.
Post Crash Management Systems highlight that whilst they are aware of the hazards of carbon fibre particles following an impact and fire situation, the company are still investigating and evaluating the effects of carbon fibres on the resipratory system. To this end John Andrews would welcome any suggestions or information from members of the composites industry dealing with carbon fibre.
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