There are a number of things that can happen when using water or vacuum extraction that can stop the dust being properly controlled. Even if this does not happen, some tasks are so dusty that enough escapes into the air to still be a risk. For this reason some form of respiratory protective equipment (RPE), usually in the form of a mask, is also needed for high risk tasks such as:
Using a cut-off saw, grinder or wall chaser on material containing silica
Using powered cross-cut saws and sanders on hardwood, red cedar or MDF
Sanding softwood in an enclosed space
Masks are available that provide different levels of protection. There are two main performance types you should ask your supplier/ employer for if working with construction dusts: FFP2 and FFP3. FFP3 is the most advisable type to use if you are doing work that does or could create high dust levels or involves silica or wood dust (the more hazardous substances).
For more information on masks and other types of RPE see [Respiratory protective equipment at work: A practical guide](http://www.hse.gov.uk/pubns/books/hsg53.htm).