Hazard - is an unavoidable danger or risk. Source of danger. A hazard is a situation that poses a level of threat to life, health, property, or environment. Example : Polluted Air , Water , Radiation .
Disaster - A disaster is a serious disruption of the functioning of a community or a society involving widespread human, material, economic or environmental losses and impacts, which exceeds the ability of the affected community or society to cope using its own resources.