The key bit is this - “Work on the ballast can result in quartz dust being released from the stones, which can cause lung cancer.” (Emphasis mine)
Since the tracks are closed while ballast is being put down, tamped, etc. passengers don’t tend to be in close contact. By the time the trains are running again, much of the light, dangerous dust will have blown away and/or settled, hence the risk is mostly to track workers during certain types of work. It would pose some risk to people in nearby properties, but since the dust would be dispersed into the air it would probably drop off something like exponentially with distance.
It’s the same with all sorts of things, such as drilling through bricks, concrete cutting, etc. - in my experience tradesmen still take far to little precaution (often none) even though we now know the risks of silica dust.
Since the tracks are closed while ballast is being put down, tamped, etc. passengers don’t tend to be in close contact. By the time the trains are running again, much of the light, dangerous dust will have blown away and/or settled, hence the risk is mostly to track workers during certain types of work. It would pose some risk to people in nearby properties, but since the dust would be dispersed into the air it would probably drop off something like exponentially with distance.
It’s the same with all sorts of things, such as drilling through bricks, concrete cutting, etc. - in my experience tradesmen still take far to little precaution (often none) even though we now know the risks of silica dust.