I want to become a carrier in field of safety,health&environment.Should I do pg diploma in safety immediate or after gaining experience 2-3

I am graduate mechanical engineer from 2012.I am placed in sew infrastructure limited Hyderabad. till now joining did not come.should I do 1- join company and after gain 2-3 year experience do pg diploma in safety,health&environment 2-take admition in pg diploma in safety,health& environment