An accident is an event that has unintentionally happened, that results in damage, injury or harm. An incident is an event that has unintentionally happened, but this may not result in damage, harm or injury.
Therefore, every accident can be an incident. However not all incidents can be termed as an accident.
A near miss is an unplanned event that did not result in injury, damage or illness, but could have done so. A near miss may often leave the employee shaken up, or shocked, but they were not actually injured.
You can think of a near miss as a car running a stop sign, and nearly hitting someone coming through the intersection. Although the car got through ‘safely’, the other driver will be shaken up, and will likely feel the need to report that this has occurred so that other cars do not do the same thing. No one is injured, and there is no damage to property.