Any particulate matter is a low-level threat to computers and other electrical devices, but hard disks are among the least susceptible components because they are sealed units.
The most common and most obvious risk is that fans get gunked up and heat-sinks get coated, both of which means cooling components is harder... and warmer components have a shortened life on average.
In extreme or unusual cases, you might find that certain materials could produce shorts (say, between pins in RAM or PCI(e) card slots).
And certain chemicals, especially when combined with moisture in the air can have a corrosive effect on certain components.
For industrial environments, there are ruggedised PCs available or kiosks to house standard PCs. In the home, amke sure your PC intakes have filters and clean them regularly, and use compressed air sprays to keep fans and heat-sinks and other components dust-free. And vacuum outside regularly too!