Safety vs Security

Safety is freedom from unacceptable risk of physical injury or of damage to the health of people, either directly, or indirectly as a result of damage to property or to the environment.

Safety is an attribute of Dependability.

Dependability of a system is the ability to deliver service that can justifiably be trusted. Dependability is a measure of a system's availability, reliability, safety, integrity and its maintainability.

Security is the prevention of illegal or unwanted penetration, intentional or unintentional interference with the proper and intended operation, or inappropriate access to confidential information in industrial automation and control systems. Security is a composite of availability, confidentiality and integrity.

• Availability - readiness for correct service (usually expressed as a percentage of uptime in a given year)

• Reliability - continuity of correct service (typically expressed as a probability of failure-free system operation over a specified time)

• Safety - absence of catastrophic consequences or severe injuries on the users and the environment

• Confidentiality: absence of unauthorized disclosure of information

• Integrity - absence of improper system alteration

• Maintainability - ability for a process to undergo modifications and repairs

Functional safety is part of the overall safety that depends on a system or equipment operating correctly in response to its inputs. including the safe management of likely operator errors, hardware failures and environmental changes.

IEC 61508 is intended to be a basic functional safety standard applicable to all kinds of industry.