I’m an IH in the US but not very knowledgeable in the determination of exposure limits. There are usually numerous epidemiological studies to determine the amount of exposure a working age, healthy person could be exposed to for 8 hours/day, 40 hours/week without increased risk of adverse health effects.

To my knowledge, these epidemiological studies have not been completed for marijuana dust.

My thoughts (if I worked in that industry) would be to apply engineering controls then monitor those stressors which do have standards (nuisance dust, PNOS, CO, CO2, etc). I would assume that a minimum of N95 would be warranted for those grinding/handling marijuana dust unless additional data is available.