Who is the first person to inform if you have an incident or identify a hazard even if no-one is injured?

the company person number (that was posted on the emergency plan), usually will be the safety supervisor or EHS Manager it is back to the organisation size or work volume.

And one of the important reasons to inform incident even if no-one was injured, that is to know and analyze the root cause of incident that will help to avoid recurrence of the incident in the future. Also to take immediate action to eliminate the hazard.

Your Immediate supervisor and then the Safety Officer

In case of an incident,I will first  inform my Supervisor.

All incidences must be recorded by the concerned dept which has to be noted by the department head and safety officer/Manager,such recordings must be discussed in routine Management reviews.However depending on the seriousness of the incidence or a hazard, Risk analysis must be done to ensure there is  an corrective action to mitigate the risk factor.The action must be communicated to seniors

You have to inform your immediate supervisor or manager regarding the incident. If someone is injured: Inform your health personnel Note. Make sure that the incident is properly documented.

Any person who witnessed the incident or hazard or which by protocol relayed through the safety person in the area for immediate intervention as necessary and then finally to reported. In case if injury incident, the medical person will report to the safety and project management. 

this depends on the company emergency/incident reporting/contact tree sheet

most of the times its the direct supervisor, but depending on the case or the incident, sometimes you are obligated to contact the emergency response team first

You have to inform your immediate supervisor or manager regarding the incident.If someone is injured Inform the site ambulance car and inform the site doctor

To CSO - OR Designated Security Incharge as stipulated by the Company policy (ISPS - Security Plans)