ON WHAT BASIS DO RISK ASSESSMENT NEED TO BE REVIEW?

sorry for late, 

• Check that your control measures are working.
• Review your assessment in case things have changed and record the significant findings with your risk assessment documents.

Risk Assessment reviewed if necessary when changes of legislation, location of activities... etc

Risk assessment acording to the work like hot work exm......cutting grinding, observed what is the risk.1 no PTW / qualified & certified person / clear area work PPE. 

If some thing hapend what is the preacoution......ete

risk assesment needs to be reviewed only to check out that the planning you have made to control risk was valuable or not,,,  i think this is the only reason to review....