Besides the danger of engine fans and belts, etc., if you decide to work on the injector/fuel system while the engine is running, please wear eye protection and leather gloves. Fuel injector systems run very high pressure and can inject fuel through your skin. This has the potential to be a fatal injury.
A good way to check for fuel spray is to pass/wave a piece of cardboard all around the injector and lines. If it comes out dry, go ahead if you are so inclined. If it comes out streaked with spray--shut off the engine.
Regards,