you are doing some serious mistakes there.
never under any uncontrolled circumstances open a hot radiator cap unless
a - you are devdas and your girl left you
b - you have been caught by your wife while on a date with girlfriend
c - you have no will to live peacefully ever again
2nd and 3rd degree burns are not fun - they are very painful..
Under normal condition the hose pipes will be hard with pressure (radiator cap is doing its job and system is tight), Any mechanic telling you otherwise needs to be handed over to a museum as a historic artifact - only cars from the 1930s had a convection cooling system with no pressure.
When you open the cap the system is under normal 1 atm pressure - this will cause water to boilover - with cap installed the system will self pressurize and hence increase the boil point - which wont happen because the cap will release the coolant/water to the expansion tank at anything above 1+1 atm.