It's safety is basically completely a function of the operator. Since the beam will keep depositing energy (ie heating), if the beam is held on a target, it will incur more and more heating (and potentially harm).
In proper usage, safety is ensured through the combination of operator training, selection of proper settings, and induced compliance. If you have a shitty operator, risk of over exposure increases. The nature of this device means that it's not a barrier, it's a beam.
During earlier testing, they were able to induce second degree burns on a test subject due to incorrect power and duration settings.