Presumably these are antennas for transmission? If for receiving then, obviously, the risks would solely be due to their location and possible physical hazards - slips, trips and falls; cuts etc.

If they are attached to transmitters then you're entering into the possibility of harm through exposure to electromagnetic radiation. Best case the transmitters can be turned off for the duration of your works - here I'd be looking for lock-off/tagging as controls to prevent inadvertent activation. If they cannot be turned off then you'll need to seek expert advice with respect to the power and frequency of the output and the directionality of the antennas to properly assess the risks.

If it were me I'd be pushing hard to schedule the works in conjunction with system downtime. EM radiation is insidious, completely invisible and potentially very harmful.

And you have to know the device is there. Micro Base stations are being installed behind GRP facias such as Petrol Station Canopies, etc.