When a security guard witnesses a worker operating machinery unsafely, posing an immediate risk, what is the most appropriate action according to OHSA principles?

1. Document the unsafe act and only report it to the Joint Health and Safety Committee (JHSC) during their next meeting.
2. Instruct another worker to confront the unsafe worker, avoiding direct involvement.
3. Observe the worker for a prolonged period to gather more evidence of unsafe practices.
4. Intervene immediately, advise the worker of the hazard, stop the unsafe work if necessary, and report to the supervisor.