Jea Thank you to take your time to try to lift this problem.
But I discovered, the variable 'firenumber' is not the fault;
I displaced "while(firenumber<5){wait(1);}" with "while(!key_space)wait(1);"
If I press space before I extinguishe one fire, it works fine. If I extinguishe one fire before I press space, nothing happens. So the fire-function must make the scenario-function stuck. So I wrote this five lines:

feuer(200,850);
feuer(130,920);
feuer(240,1000);
feuer(400,980);
feuer(270,920);

In another function and, I was amazed, it works!
To test something I replaced the "my" from the fire-function with another entity-pointer and it works with this five lines in the scenario-function also. So I ask me; why gets a function stuck, if I remove his "my" pointer?