Sir - During the 1980s, I campaigned (unsuccessfully) for the withdrawal of highly toxic Halon 1211 portable extinguishers from flightdecks and cabins, suggesting their replacement by five-times-safer Halon 1301.

My fear was - and remains - that 1211, in the confined space of a flightdeck, could cause the crew to be overpowered by the melange of toxic fumes released by the Halon when mixed with smoke and poisons emanating from burning plastic, wiring, etc.

The sole argument raised against 1301 was that it lacked the "throw" of 1211, but throw is unnecessary on a flightdeck because of the confined space. Neither is throw required in a cabin fire, which must be tackled at close range - about 225mm (9in), according to UK Civil Aviation Authority experts who conducted comparative trials at Teesside in 1987.

Halon 1301 is also more effective in penetration of panels, or areas where concealed fire may be at work, because it is pure gas, while 1211 emerges as a semi-liquid spray, with less penetrative power and can even "splashback", causing injury to the operator.

Press reports (possibly premature) suggest that the pilots could have been dead before the ValuJet McDonnell Douglas DC-9 entered its final dive on 11 May.

With smoke reported in the cockpit, could use of Halon 1211 have overpowered them, or rendered them unable to control the aircraft?

The results of the CAA comparative testing of 1211 and 1301 were not reported, although I had a letter from then-chairman Sir Christopher Tugendaht, confirming that 1301 portables proved to be as effective as 1211 ones in the aircraft-cabin simulation. If they worked, and are so much safer, why not use 1301 portables?


London, UK

Source: Flight International