We have a CNC router which machines composite door slabs (wood frame, PU foam core and PVC skin). Occasionally, the tungsten carbide bit snaps and the 'stump' continues to rotate on the snapped off part (which remains embedded in the slab). Sparks are shot up the extraction system until someone stops the machine. To me, this is a significant explosion and fire risk, although the manufacturers are being fairly non-committal. The manufacturer quotes ignition points for the PVC and wood at around 220 and 400 deg C respectively. Don't know about the PU foam yet. Obviously a dust / air mixture will burn a lot more readily than a solid. So, firstly do you reckon there's a level of risk high enough to worry about here? And secondly, given that we've done all we can to prevent the cutter bit snapping already, what could be done to prevent the sparks causing a fire or explosion?

PhilW, That look like just the job, Many thanks

Dear Aunt. You are taking the right approach to prevent these sparks. However as you are handling combustable dusts in systems, you should be Risk Assessing the extraction system under DSEAR http://www.hse.gov.uk/fireandexplosion/dsear.htm. This will become the supporting case as to whether you add flame detection and supperssion or do something else. Most Dustraction systems rely on mitigation using BSEN1127-1 6.5.3 "Explosion relief". i.e. explosion bursting panels. This may be a cheaper route than a full suppression route and certainly if you can fit broken tool detection which will remove the ignition source. best wishes Peter