(b) That's probably wrong. Dust is certainly one of the aspects of ordinary life that cannot be avoided, and to an extent, everyone is expected to put up with a reasonable amount of dust and clean it up as required.
But causing a deposit of dust can amount to actionable harm if the dust is excessive and lessens the value of the plaintiff's property. Large amounts of dust which impregnate and discolour soft furnishings probably falls within this test. The effect of dust in these circumstances may well lessen the value of the plaintiff's property, but if it could only be shown that the use or enjoyment of property was impaired, this would probably be insufficient.