B747-400 Captain reported a fueler at his aircraft was almost hit by the extension of the leading edge slats during maintenance action.

Narrative

Upon arrival outside the aircraft; we noticed the fueling and loading operations were underway. The fueler was up on the basket and connected to the aircraft. Suddenly the LE slats deployed; catching the fueler by surprise. The fueler put his hands up and ducked away from the slats. The FO (First Officer) was doing his walk around and was equally surprised by the movement of the slats. The LE slats did NOT strike the fueler and did not contact any equipment. We got lucky. I questioned the maintenance man performing the slats check; he told me he told the ground staff he was moving the flaps. I don't know who he told but the fueler did not get the word nor were any safety personnel in place outside the aircraft.Safety personnel need to be in place outside the aircraft and able to keep the area around the moving devices clear. Ground communications need to be established with a safety observer. Fueling needs to be suspended during flap operations on the ground.