Communication and signalling, including whistle, hand and radio signals and exclusion zones
Signal systems
Effective communication is critical for safe crane operation. There are three main methods: hand signals, whistle signals, and radio. Hand signals must be given by a designated dogman or rigger, and the operator must stop if signals are unclear. Whistle signals are used for emergency stop (one long blast) and other commands. Radio communication requires clear, concise language, and the operator must confirm understanding. Only one person should give signals at a time; if multiple, the operator must stop and clarify.
Exclusion zones
Exclusion zones keep people away from the crane's slew radius and load path. They must be marked with barriers, signs, and if necessary, a dedicated spotter. No one should stand under a suspended load. The dogman must ensure the area is clear before signalling to lift.
Traps in questions
Questions often test the emergency stop signal: it is one long whistle blast or a hand signal (both arms raised). Another trap is assuming radio communication is always required; hand signals are acceptable if visible. Also, the operator must obey a stop signal from anyone, not just the designated signaler. Remember that the signaler must be in view of the operator; if not, radio or relay is needed.
Worked example / rule of thumb
Rule: If you lose sight of the signaler, stop immediately. If you hear any emergency stop signal, stop regardless of who gave it. Example: A dogman gives a hand signal to slew left; the operator confirms and moves slowly, watching the load and signaler.