As you may be aware, PVC pipes - generally speaking - will readily become electro-statically charged, allowing for electrostatic charge buildup, and potential discharge. It is therefore suggested to avoid the use of insulating pipes such as PVC. You may consider using a cardboard pipe instead. Additionally, PVC could also produce hot, melted plastic debris that could pose a hazard.

The particulates and air escaping out the fuse hole could also be of concern. A very small amount of puffing may not pose a problem, however it may, depending on many factors. As you do a number of these in sequence, you may get a hazardous accumulation of particulates in the work area, on clothes, skin and hair, etc. This could result in a hazardous situation where any spark, heat, impact or friction event could result in a virtually instantaneous conflagration. In the process design I would include adequate humidity, bonding and grounding, and ventilation/capture of explosive particulates, and would design the process so as to avoid the escape of air/particulates.