If individuals are working outside the range where others can call or see them, this is referred to as working alone. Working alone in a situation which is not classified as being hazardous is generally not a problem.
DGUV Regulation 1: "Principles of Prevention" defines hazardous tasks (please refer to Sec. 8) as being activities which - due to the type of activity, the substances used or the working environment - pose increased risks. Working where there is a danger of falling is explicitly used as an example.
Completing dangerous tasks on one’s own is only possible under special circumstances. In this case, the employer must take appropriate measures to monitor the person who is working alone. An example of such a technical measure would be the use of a suitable personal emergency alarm system in accordance with DGUV Rule 112-139. An example of an appropriate organisational measure would be the use of a permanently-installed video surveillance system. However, care must also be taken to ensure that in such cases, a rescue operation can be immediately initiated and carried out without delay in the case of a fall. The respective monitoring measure and the rescue concept must guarantee this. If this is not the case, it is not possible to work alone.
As long as the wrong usage of a preventative fall protection system, such as a retention system , is virtually ruled out, you could potentially work alone. However, you must then also ensure that the nature of the work, resp. the substances used, do not pose any additional risks. Otherwise, working alone would, once again, be potentially dangerous.
When using a guided type fall arrester equipped with a flexible anchor line as a retention system, one should be aware of the fact that a simple operating error could lead to a fall. Even when a retention system has been installed, it is not that easy to work alone safely. These risks must be given due consideration in your risk assessment.