SQL & PL/SQL

I have a question about global variable scope. I have one package named PKG_GLOBAL_VARIABLE where in I have declared few variables which are being used by the trigger.

Now I have one row based and one statement based trigger. In row based trigger I take the value of :new and :old values and assign it to the global variables and then in the statement level triggers I perform operations with the help of these values. All this is happening in one transaction. I wanted to know what will happen if simultaneously more than one transaction is occuring? What will the values of these global variables? Will it be transaction specific? Also what are the possibilities when there can be issue with the values assigned to global variables.

Thanks for help in advance.