Safety and Reliability are the same?

No. Safety and reliability are often linked but are not the same thing. Safety is defined in the IEC 61508 standards as “freedom from unacceptable risk.”

A safe system should protect from hazards whether it is performing reliably or not. Safety engineering assures that a safety system performs as needed, even when pieces fail. In fact, safety engineers assume that systems will fail, and design accordingly.

Reliability is a measure of how well the system does exactly what it is intended to do when operated in a specific manner. A reliable system may not always be a safe system. The challenge in functional safety is to ensure that a system is both reliable and safe.