I was told by staffers at Fermilab that it was once not uncommon for experimenters to stand in the experiment blockhouses and manually position detectors in the beam. Sometimes maybe even traversing the beam in front of the beam-dump. Not the main ring beamline of course, that would probably be fatal, but the at the Meson Test Beam line. Nowadays those areas are locked out such that breaching the area would shut off the beam before you could reach it. Of course, it was probably locked-out then as well, but now you'll be thrown off the premises if you break the lock.