Dear Mr. Ashok
First of all let me welcome you into the forum... This is a great forum where people sharing their knowledge and experience with an open mind... Hope you will get benefit from this forum...
Now let me answer to your queries...
Hazard - Anything that has the potential to cause harm.
Risk: The likelihood (probability) that someone will be harmed.
Risk = Exposure X Severity X Probability
Risk Assessment - A systematic and structured process whereby hazards present in a workplace, or arising from workplace activity, are identified, risks assessed/ evaluated, and decisions prioritized in order to reduce risks to acceptable levels. Go through the attached file for more understanding on the topic...
While defining the control measures, the prevention hierarchy needs to be taken into account. Highest priority is to be given to elimination:
1. Elimination :Elimination of hazard
2. Substitution: Reduce risk at source or remove source
3. Engineering Control : Intervention of engineering solution
4. Administrative Control : As defined in JSA/ SWP, Work instructions & Training
5. PPE : Make people wear PPE
Hope this helps you somehow...