According to Boeing, there have been 33 reported ingestions of personnel into an engine on 737-100/200 airplanes since 1969.
All ground personnel who work near airplanes need to know the locations of the engine inlet and exhaust hazard zones with engines at idle and above idle thrust.
These hazard-area warning decals are located on both left and right engine nacelles
Prior to start the engines, Pilots first turn on the beacon or Anti-collision light (depends on the Aircraft type), and get a Verbal and Visual confirmation from the ground crew that they have left the hazard area and then start the engines.
Similarly upon landing, the pilots shut the engines down, wait for them to spool down and turn off the beacons. Spool down time varies depends on the engine type. The ground crew should maintain a safe distance from approaching the aircraft and ask the pilots via radio or wired intercom whether the engines are indeed off before moving close to engines.
Ground grew should familiarise the hazard zones for different types of Aircraft and under absolutely no circumstances should they enter these areas whilst an engine is operating or beacon light is illuminated.
— Crash Aérien (@crashaerien) November 5, 2017