For top loading operation the loading happens at around 3 meter above ground level and driver of vehicle does not have any view of the top. Many time it happens that the driver considering that the loading is complete and try to take out the truck whearas the loading arm is still inserted into the truck compartment. This generally damage the loading arm and this always has chance of spark and fire thereafter. I am looking for automated control to protect the loading arm. I though of placing a proximity sensor, which will detect the position of loading arm. This sensor will give signal to stepper motor, which will be attached to a level with lights. So when the loading arm is out of position then the lever and light will be in front of driver cabin else it will be away. I was looking for more idea on this or material description (flameproof) for the idea given above.

There are plenty of 'drive away' protection systems on the market. Google to find a supplier. In the meantime, the driver should turn the engine off and give the vehicle keys to the top man. He can have the keys back once the top man has finished.

Thanks Ian for giving your valuable time for this. I will certainly look for the "Drive away" protection system on internet. However your idea of handing over the keys to the top man is good and implementable.