It will scratch glass, so imagine what it does to the finer bits of human lungs. The term 'ash' reminds us of that soft, grey powdery stuff (from coal-fires) that went in the dustbins years-ago.
Pyroclastic material is very different.
It is angular/sub-angular grit and sharp, angular shards of volcanic glass.
Usually with a high Silica content. Many of the mountains NW of Lancaster are built it.
Volcanic clouds often have a high content of volatiles, CO2, SO2, HF, H2S, HCl, Flourine and Boron may also be present.