Be cautious, but I've never been squirted in the eye. Put it this way - at idle, you can pull off an injector line and count the drops. How much pressure can there be in the individual injector lines? Upstream might be a different story.

Set your wrench on a fitting, drape a rag over the fitting, then loosen the fitting. After the pressure is gone from one fitting, there won't be pressure in the others.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD