This week's Flight international quotes a maximum allowable ash concentration of 10e-16g/cuM (That's ten to the minus seventeen). This was reduced to 10e-16 to allow flying to resume.
If - if that figure is correct - and Flight is generally pretty good with accuracy- this leads to some interesting numbers...
Mass flow thru a CFM56 approx 1000lb/sec or 454Kg/sec
Air density at FL200 approx 0.5Kg/cuM
Volume flow is 900cuM/sec
or 3.24Million cuM/hr - ie 3,2 x 10e6
Times the max allowable concentration and we have 3.2 x 10e6 times 10e-16
= 3.2 x 10e-10 grams per hour of ash. That's far too small to be a hazard, by a factor of ten or a hundred billion or so, surely? There is something gigantically wrong here!
Shurely shome mishtake?
(and I hope it isn't my maths)
Standing by to be corrected!