The integrity of the original installation is a key issue. What type of location is it? Wet, Damp, Indoor? Was the proper wiring method utilized? Is the equipment in good condition? How close to the actual electrical equipment are the operators when sampling? There may be no concerns at all if all of the above are addressed. However, an equipment ground conductor is a definite.
I, personally, would perform a megger test to determine the condition of the insulation, particularly if it is subject to moisture.
Any pictures would be of great help.