Before work starts, the safety of those taking part is assessed, considering among other things: whether the people under investigation will be present and whether they may be violent; the time of day; whether bystanders can be kept away; weapons; physical hazards; devices or surroundings rigged to injure if mishandled (a concealed trap, for example); material likely to cause psychological harm or offence; whether the scene is unsafe; and how the surrounding area affects risk.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.