Is it possible to make disable Safari's window pinch?

We have made a web page for voting. Our users got an iPad to make their choices by pushing of possible answer buttons. We have used Safari to do this. Before we give iPad to a user we limited Safari's and iPad (turn off Safari's own button, and menus, protect main button with password etc.).

Everything was fine and worked well until this last iOS update. In this time user can pinch the Safari app, and he/she can push a small "X" on pinched window and can leave Safari. My question is: Is it possible to turn of this pinch movement in Safari?

(We have tested this movement in Google Chrome and this possibility is not in that app.)

Please help me!

Yours

Charlie