In which situation should the signal person refrain from giving signals?

The correct answer is when visibility is blocked or hazardous conditions are present. In these situations, a signal person must prioritize safety above all else. Effective signaling relies heavily on clear visibility; without it, the signal person cannot accurately communicate the necessary instructions to the crane operator or the crew. Hazards may include obstructions that block sightlines or dangerous weather conditions, which could compromise the safety of the operation. If conditions are unsafe, the signal person should refrain from signaling to prevent accidents or potentially dangerous situations from arising.

The other choices involve scenarios where signaling could still be conducted. For instance, if the operator is not present, the absence of the operator means there’s no one to receive signals, but this does not relate to the safety aspects of signaling during operations. Signaling during slow load movements may still be necessary for coordination and safety. While being tired can affect a signal person's performance, it does not inherently warrant the immediate cessation of signaling if the conditions themselves remain safe. The clarity of visibility and the presence of hazards are the highest priorities when determining whether to signal.