We dodged the bullet

My warm welcome to all who stumbleupon this post!
So as you all can see in the picture that is shown bellow a proppeller is starting to move and scrapping what appears to be a metal cube.
Well...let me explain...
This was in a german shipyard and the vessels name was "Hammonia Antofagasta" . This vessel was a old container that needed some fixes . During those fixes the company superintendent whent inside the engine room and with the chief engieer started to test the proppeler.
In that time with no knowledge the crew of the shipyard (not of the ship) from under the belly of the ship where chipping the proppeller and put a container filled with fuel .
Before begining the test the chief asked if someone was down, and of course everyone was busy with maintenance and repairs.
With the Chief Officer I went down and started to clear the way of workers because nobody knew about the test .
Mission completed, all workers clear the proppeller side.
Its important to say that we informed what type of test it will be....but nobody informed us about the fuel container.
After all workes left the area, I (3rd officer) inspected the area and found that the test canot be made ...and i urgently called:
Stop Stop Stop DANGER !
Test was stopped in time and nothing was damaged .....if the test would have gone as planned me and many more would be DEAD!
I informed what type of situation was down and fixed the problem in ample time (about 5-6 min). The proppeler was stuck in the cube but we managed to take the cube out of the way.
What is the conclusion ?
Don't trust nobody and double check everything even triple check just to be sure.
Communicate with all the workers, stevedores, officers or other and be sure that everything is in order.
I will not waste my second chance of life, I will do my job and ensure not only my safety but the safety of the crew and ship.