To protect your lungs the Control of Substances Hazardous to Health (COSHH) Regulations (see also Workplace Exposure Limit or WEL). These limits are not a large amount of dust. To give an example the image below shows the maximum amount of silica you can breathe when averaged over a normal working day.
When compared to a penny it is tiny – like a small pinch of salt:
'This limit is the legal maximum, the most you can breathe [b]after[/b] the right controls have been used. For tasks that can create high levels of silica and wood dust these controls have to be very good as the risks from these dusts are high.