Health impact assessment is a support tool for intersectional decision and policy-making. It is employed to assess the potential health consequences of pending decisions and it feeds this information back into the decision making process hence the following definitions use intervention to cover intended action construction regulatory changes, provision of service, educational activity, construction of infrastructure and provision of welfare benifits thereby to choose the most benifitcial of health and equity.
There is no single correct method of HIA as it is applied to an enormous range of decisions, varying from international policy to very local projects and an equally mid range of topics. The appropriate method varies according to the particular question under consideration.
In Thailand showed an impact of health from factories town such as at Mabtapud in Rayong province. It makes chemical substance flowed in the air or water into residence area affect to health status include sickness to severe of sickness and death in the finally. HIA is the essential tool for use in this area and make outcome for solving this problem or choosing the most beneficial of health and equity to them.