Does someone who live within 5km of chemical plant have higher incidence of lung disease than a person who lives outside?

No magic numbers. If the plant is run properly and regulators have done their job airborne risk should be low. If present it is related to prevailing winds with increased risk in downwind locations. If pollutants reach the water supply, carcinogens can reach the lungs in a rather large area.
Air quality. Several forms of lung disease can develop after exposure to many different types of inhaled pollutants. The risk for these disorders depends on air quality in the area in which you live. Distance from factories, wind patterns & types of effluents (their density & constituents) also determine this risk. Consult your local health dept to find out more about air quality in your area.