First, discuss with his colleague (who is performing) about the unsafe practice and the risk involves result in this practice. Then he can show the safe way to do and explain how it minimise the risk. Any unsafe practice should be recorded and reported to the manager in order to be corrected informing all of the staff by providing training or necessary information. If manager does not hear you or nothing come in action to eliminate unsafe practice then you have all the way right to complain to the social service, CQC, health and safety commission and department of health. But first you must follow all the procedures of complaints within the organisation you are working or the organisation where unsafe practice took place.
